WO2011148139A2

WO2011148139A2 - Solar power generation

Info

Publication number: WO2011148139A2
Application number: PCT/GB2011/000807
Authority: WO
Inventors: Ian Humphrey-Smith; Clive Rankin
Original assignee: SOLAR COVERED LANDFILL Ltd
Current assignee: SOLAR COVERED LANDFILL Ltd
Priority date: 2010-05-25
Filing date: 2011-05-25
Publication date: 2011-12-01
Anticipated expiration: 2012-11-25
Also published as: WO2011148139A3

Abstract

The present invention relates to a method of solar power generation applicable to landfill sites. A landfill comprising waste material is covered by a solar power generating layer, which provides a barrier to gas escaping from the waste material to the atmosphere above. The solar power generating layer comprises a flexible sheet material having solar power generating means bonded thereto for producing electric power from sunlight incident on the landfill. The flexible sheet material may comprise a geomembrane, such as a PVC sheet, and the solar power generating means may comprise thin-film solar cells. The solar power generating layer may comprise a continuous or discontinuous sheet, and in the latter case it may comprise a number or sheet units adjacent to each other, the edges of the sheet units being bridged or held together by fluid-impermeable holding means. The solar power generating layer is optionally laid over a support structure.

Description

Solar Power Generation

Field of the Invention This invention relates to combined power generation from landfill sites by solar means and from captured landfill gas, using a single integrated approach. It further relates to landfill site installations which are provided with the means for such combined power generation, and which are economical to construct, and have good accessibility and/or drainage, and to methods for producing such sites.

When used herein, the following terms have the following meanings:

"Adjacent" herein in relation to the edge portions of sheet units means that the edge portions overlap, abut, or are close to each other. It is preferred that they overlap.

"Asphalt rubber" means (as defined in 1988 by the American Society for Testing and Materials (ASTM) ASTM D8-88) a blend of asphalt cement, reclaimed tire rubber and certain additives, in which the rubber component is least 15% by weight of the total blend and has reacted in the hot asphalt cement sufficiently to cause swelling of the rubber particles.

"Base layer" means a flexible layer of a fluid impermeable material above the decomposing material in an installation and below an overburden, holding means and/or support structure.

"Capping assembly" means an assembly which may be constructed directly on top of landfill decomposing material, but preferably on a capping support layer with a relatively even surface constructed on the landfill material, and which comprises a solar power generating layer, optionally laid over a support structure.

"Capping support layer" means a layer or stratum, often including for example clay, earth, ash, and/or other particulate material, by which the decomposing material in a landfill is covered over. Any support structure is often built above the capping support layer, rather than on the decomposing material. "Depression" in relation to a landfill installation of the present invention means any hollow or low spot, such as a basin, or an elongate hollow, such as a channel, furrow or valley between units of a support structure, such as mounds, on the upper surface of the installation.

"Fluid" includes gases and liquids.

"Fluid-impermeable" in relation to any layer means that the layer is significantly impermeable to gases and liquids.

"Installation" and "site" means any installation comprising decomposing material, such as a landfill or a dump containing decomposing waste material (for example unwanted, unused or unusable rubbish, trash, refuse, garbage, or junk), such as organic waste material; or a silage clamp containing decomposing waste material (for example fermenting material of biological origin, such as grasses, seaweed, wood, leaves or hay).

"Mound" herein includes a unit of a support structure which has any structure such as a heap, pile, stack, hillock or knoll, or an elongate such structure such as an embankment or ridge.

"Protective layer" means a layer in contact with the underside of the solar power generating layer which protects any heat welds or areas of adhesive between any component sheets and/or sheet units of the solar power generating layer from abrasion or other deleterious action of any material beneath it.

"Solar cap" in relation to a landfill installation of the present invention means a portion of a solar power generating layer which is borne by a unit of the support structure, such as a mound. It passes from at least one depression adjacent to the unit over the top of the unit to at least one other depression adjacent to the unit.

"Solar power generating layer" means a layer comprising an impermeable flexible sheet material providing a barrier to fluid escaping from and/or entering the mass of decomposing material in a landfill installation. The sheet has solar power generating means bonded thereto for producing electric power from sunlight incident on at least a portion of the installation.

"Sheet unit" in relation to a layer such as the solar power generating layer, protective layer or base layer. Each of such layers comprises a number of fluid- impermeable sheet units bonded together or adjacent to each other, as defined above, each sheet unit being as supplied from the manufacturer or a relatively large sheet unit comprising a number of smaller sheets bonded together. "Support structure" means any assembly or construction on the decomposing material in an installation or a capping support layer for supporting a solar power generating layer.

Background to the Invention

When garbage (municipal solid waste) contained within landfill or dumpsites is compressed over time there is very little room for any oxygen. When bacteria break down the garbage, it creates a landfill gas, which contains methane, hydrogen and carbon dioxide with small amounts of nitrogen and oxygen.

In conventional best practice, an engineered landfill site for garbage (municipal solid waste) is lined inter alia with a water-proof plastics liner before the waste material is added to the site, to minimise loss of leachate to ground water. It is important to note that compressed garbage does not generally allow landfill gases to permeate the body of waste uniformly. Landfill gases can accumulate in pockets and as a consequence permeate out of the landfill mass at disparate rates across a landfill site. Also in conventional best practice, capping the landfill with a continuous fluid- impermeable layer above the mass of waste prevents the gases produced by the decomposition of the waste from escaping in an uncontrolled manner, and hinders rain water from entering the landfill, thereby hindering the loss of leachate to groundwater, which is important in areas of high rainfall. Conventionally, the impermeable capping layer is covered by one or more layers of gravel, rock, ash, clay, and/or soil, which protect the capping layer and can be planted with vegetation. Geomembranes are also often employed as part of the surface capping and/or lining process. Geomembranes are impermeable sheet materials, generally provided in the form of a roll, which is laid over and/or under the mass of waste and are generally protected by a layer or stratum of clay and/or sand. Adjacent sheets of geomembrane are traditionally fused together by thermal welding and/or bonded with adhesive to form a continuous sheet of material that is largely impenetrable by gas or liquid. As a result, the geomembrane ensures that little or no liquid leachate escapes from the bottom of the landfill, no landfill gas escapes except by controlled extraction, and little or no rain enters the landfill.

The landfill gases are mostly methane, hydrogen and carbon dioxide with small amounts of nitrogen and oxygen. In addition to the geomembrane covering and in order to prevent the gas from exploding or bursting into flames, a system or series of pipes are embedded within the landfill to extract the gas and / or vertical drill casings (perforated porous vertical piping) is inserted into the landfill mass. In some cases, this gas is vented or burned off.

Since the landfill gases are mainly methane, they can be extracted and used for electricity or heat generation. In such a case, vertical porous or perforated riser shaft gas collection pipes or drill casings made of metal or plastics are installed within the layer of compacted rubbish and thereby remove the landfill gas to a gas well head. The aim of the gas collection system is to extract the maximum possible volume of gas but to leave condensate behind; landfill gas is warm and saturated with water. Typically a well head will monitor and regulate the gas flow from each well, and also contains a barometric leg for draining condensate away. The gas flow regulation device used is usually a sleeve or butterfly valve type and allows for condensate collection. Landfill gases are then pumped to a burner, for example of a steam generator, or though a methane and/or hydrogen recovery unit to a gas turbine engine, and the steam generator or engine powers an electrical generator. In developing countries, the size of landfill / dumpsites sites can reach over 100 hectares, and can be located in ecologically or hydrologically sensitive areas. As the size of the landfill site increases the task of sealing the geomembrane sheets into a continuous sheet becomes increasingly cost- and time- intensive, as does the collection of landfill gases for power generation.

Hence, the bulk of landfill sites internationally are generally operated below optimal standards of sanitary practice, and are primarily open dumps without leachate retention, rain exclusion or gas recovery systems. Uncapped and non- engineered landfill leads undesirably to toxic leachates making their way into surrounding surface and subterranean waters.

As noted above, landfill sites may be capped with a fluid-impermeable flexible layer, often a continuous geomembrane, which hinders rain entering the decomposing material in the landfill. Even then, drainage and/or means to remove dirt or debris from its surface are usually wanting or inadequate, especially for areas of high rainfall, and the formation or stagnant puddles or even pools and/or the accumulation of dirt or debris on the impermeable surface may result. All these factors can lead to landfill sites provide a breeding ground for the common housefly and rats, and particularly in tropical locations, mosquitoes, leading to increased risk of transmission of diseases, including such diseases as yellow fever and malaria. As a further result of the formation or stagnant puddles or even pools and/or the accumulation of dirt or debris on the impermeable surface, access to the top of the layer, for example for maintenance, is often not good.

A problem associated with power generation from new engineered landfill gases is that there is typically a delay of one to two years from completion of the landfill site, or part of a site, before power generation can begin. This is usually to allow time to produce sufficient volumes of landfill gas to justify the investment in a methane and/or hydrogen recovery unit and gas turbine plant for power generation from the gas. The prior art provides a landfill site capped with a fluid-impermeable flexible layer, often a continuous geomembrane providing a barrier to gas escaping from and/or rain entering the decomposing material and another fluid-impermeable flexible sheet material bearing solar panels producing electric power. The power generated may be used locally, or may be converted to AC for input into an electricity grid or a micro-grid. This provides power generation until and after the landfill gases come on stream, and significantly increases the power produced per unit area of landfill site, and provides the advantage of a highly cost-effective source for the provision of inexpensive, reliable renewable energy generation. This may be of particular benefit in developing countries, particularly where the efficiency of solar energy generation is enhanced by the position of the tropical sun near to zenith for a substantial fraction of each day, so that all areas of a landfill site receive direct sunlight, regardless of the location or profile of the site. Whereas sealing a landfill site can be expensive, the solar power generation capability obtained by installing a solar capping layer can be used to offset these costs. In particular, solar capping can increase the Certified Emission Reductions (CERs) generated under the United Nations Framework Convention on Climate Change (UNFCCC) Clean Development method project, thereby reducing the initial cost of project implementation and electricity generation.

However, each of the support membrane and the solar power generating layer is usually constructed of component sheets joined together by thermal welding and/or adhesive to form a continuous sheet of material that is largely impenetrable by gas or liquid. As a result, not only is the installation process labour intensive, time consuming and/or expensive, but cost and effort are duplicated in the two layers. As a result, such systems are not yet used to date on a large scale in developing countries. In addition, where drainage and/or means to remove dirt or debris from its surface are wanting or inadequate, especially for areas of high rainfall, giving rise to the formation of stagnant puddles or even pools and/or the accumulation of dirt or debris on the impermeable surface, access to the top of the landfill, for example for maintenance, is not good.

The present invention seeks to overcome the above problems of the prior art.

Summary of the Invention

According to a first aspect of the present invention, there is provided an installation for generating solar power, comprising:

a mass of decomposing material; and a solar power generating layer, in turn comprising a fluid-impermeable flexible sheet material providing a barrier to fluids escaping from and/or entering the mass of decomposing material to/from the atmosphere above and solar power generating means bonded thereto for producing electric power from sunlight incident on at least a portion of the installation.

The solar power generating layer may comprise a continuous or discontinuous sheet. It may typically comprise a number or sheet units bonded together to form a continuous layer or adjacent to each other, as defined above, to form a discontinuous layer.

Whether continuous or discontinuous, it is preferred that the solar power generating layer forms a fluid-impermeable layer, of material that is largely impenetrable by gas or liquid, above the mass of waste in the installation to prevent the gases produced by the decomposition of the waste from escaping in an uncontrolled manner, which can then be reliably extracted at individual points from the waste material, and to hinder rainwater from entering the installation, thereby hindering the loss of leachate to groundwater (which is important in areas of high rainfall). In the embodiment of the invention with a discontinuous layer, it is preferred that the edges of the sheet units comprised in the layer are bridged or held together by fluid-impermeable holding means. In this way the resultant layer is fluid- impermeable, with the same advantageous properties as regards gas containment and rainwater exclusion as a continuous layer. .

Advantageously, the present invention performs a dual role, capping the landfill and providing a means for generating solar power. As a capping layer, the impermeable layer prevents escape of landfill gases to the atmosphere, thereby facilitating methane capture for energy production, and prevents the infiltration of rainwater, thereby reducing contamination of the groundwater and nearby surface waters by leachates. The solar power generating layer enables a landfill to be used for generating solar power, in addition to, or instead of, generating power from captured landfill gases produced by the decomposing waste material. The installation of the solar power generation means and the capping of a landfill site can therefore be achieved in a single procedure, reducing costs.

A further advantage is that the present invention allows power to be generated immediately on completion of a landfill site, or a part of a site, whereas there is delay of typically 1-2 years before sufficient methane is produced for methane power production to be economically viable, due to the slow initial rate of methane production from degrading refuse. Solar power production can, in principle, continue for the 20- to 25-year life-span of the methane production cycle.

However, the solar power generating layer can also be used to increase the rate of decomposition of the refuse by bacteria, by increasing heat transfer to the decomposing waste. For example, a black or dark-coloured sheet material (for example a black or dark-coloured geomembrane) can be used to maximize heat transfer to the underlying waste. The dark colour of most solar power generating means, in particular thin film solar cells can further boost this effect. Alternatively or additionally, electricity generated by the solar power generating layer can be exploited locally to heat air that can be pumped to the base of the landfill so as to increase the rate of methane production by degrading bacteria. Yet another advantage is that the flexible sheet material can conform to the shape of the landfill, the solar power generating layer may move up and down with varying sedimentation and compaction rates of landfill and dump sites, and the sheets may be rolled for transport and unrolled and used in the installation.

According to a second aspect of the present invention, there is provided a method for constructing an installation for generating solar power, comprising the step of covering a mass of decomposing material with a substantially gas- impermeable flexible sheet material, wherein said sheet material has solar power generating means bonded thereto.

In a first preferred embodiment of the first aspect of the present invention, the installation comprises a capping assembly above the decomposing material, comprising the solar power generating layer installed on a support structure which comprises at least two man-made mounds (as defined hereinbefore).

The support structure may (less usually) be on the surface of the decomposing material (typically in a landfill). In general, the decomposing material is covered over with a capping support layer, including for example clay, earth, ash, and/or other particulate material, and the support structure is on the capping support layer. The support structure raises the sheet material and solar power generating means above the level of the decomposing material and/or the capping support layer. Advantageously, this renders the solar power generating means less prone to damage. The surface of each mound is sloping, so that any rainwater, soil, dirt or debris will be swept downhill under the influence of gravity, wind and rain, which reduces the formation or puddles or accumulation of dirt or debris.

Such accumulation may otherwise occur on a level installation surface and reduce the power generating efficiency of the solar power generating means, lead to an increased risk of transmission of diseases such as yellow fever and malaria, and/or impair access to the solar power generating means, for example for maintenance. Preferably, at least a portion of each mound surface has a slope of at least 5 degrees to the horizontal, more preferably, at least 15 degrees to the horizontal, in particular at least 25 degrees to the horizontal. These angles may be measured in any direction on the surface of the capping assembly, but preferably in the direction of greatest slope. Where the installation is in an area significantly far from the equator some of the sloping side walls may usefully be at an angle to the horizontal, and face in the direction, that maximises the amount of sunlight falling on the solar power generating means.

The mounds may each be a hillock or hummock or they may be elongate ridges, in each case with elongate depressions between them, the side walls of which are formed by the sheet units of the solar power generating layer. The depth of the depressions will depend on the angle to the horizontal of the side walls, and at lower angles, they will be relatively shallow.

Preferably, in the present installation, the support structure comprises a series of mounds, separated by elongate depressions, such as furrows or channels, generally in a rectangular grid pattern. In this way, at least a portion of the solar power generating layer is undulating. The support structure thus rises and falls over the mounds and depressions, and forming a 'solar cap' over each mound, the sloping walls of the solar caps defining the side walls of the elongate depressions in the capping assembly. The mounds may be produced on the surface of the capping support layer prior to laying down the solar generation layer on the capping support layer, so as to introduce mounds and undulations beneath the layer.

The desired angle from the horizontal of the side walls, and the stability of the surface slope of a heap or pile of any given material at that angle will determine the materials used in the mounds.

The solar cap mounds may comprise one of more of gravel, rock, ash, clay and soil. Alternatively, the mounds may be produced by placing boulders or rounded and/or porous structures made or metal, wood, plastic, concrete or any other like material on the surface of the capping support layer. In a preferred embodiment of the invention, each mound comprises a continuous or discontinuous layer of boulders and/or gravel, which .may have a mean size of >1cm in diameter, for example >20cm in diameter, >50cm in diameter or >100cm in diameter. The interstitial spaces between the boulders or gravel allow for relatively unimpeded gas permeation through the capping assembly. This situation differs significantly from the remainder of the compressed mass of waste material which is far from uniform or easily permeable to landfill gases.

In this manner, landfill gases that have escaped capture by conventional vertical porous or perforated riser shaft gas collection pipes or drill casings installed within the decomposing material can make their way more easily to the underside of the solar power generating layer in each solar cap and accumulate at or near to the summit of each solar cap, and can be reliably extracted at specific points from the solar caps in the installation, and dealt with as further described hereinbelow.

The undulating structure performs a number of advantageous functions:

As noted above, some of the gases from the decomposing waste passing through the mound beneath each solar cap will accumulate and be captured at the highest points of the solar cap, facilitating their processing for energy production.

The sloping side walls also reduce the formation or puddles or pools of rainwater, and the accumulation of dirt or debris on the solar power generating layer, which may otherwise reduce the efficiency of the solar power generating means. The slopes of the solar caps also channel rainwater and dirt or debris into the depressions, from where it may drain from the top of the capping assembly, which is especially useful in areas of high rainfall such as the tropical and equatorial zones, and even temperate western maritime zones. The bottom of the depressions may be configured to be relatively flat and/or broad, so that they may be advantageously used to provide access thoroughfares, such as pathways or walkways between the solar caps, for example for inspection and maintenance.

It is preferred that the upper surface of the solar power generating layer in those bottoms should bear no solar power generating means. The latter would render any the solar power generating means in the bottom of the depressions prone to damage, especially where such solar power generating means may comprise flexible thin-film solar photovoltaic cells. Additionally, the slopes of the solar caps also channel rainwater and dirt or debris into the depressions, from where it may drain from the top of the capping assembly, and the transient accumulation of rainwater, dirt or debris on the bottoms of the depressions will tend to reduce the efficiency of any solar power generating means located there.

The solar cap mounds may often be so constructed that all the sloping side walls of the sheet units of the solar power generating layer, or in the case of square or rectangular sheet units, the two members of a pair of opposing side walls are inclined at the same angle to the horizontal.

As noted hereinabove, preferably the surface of the decomposing material is covered with a capping support layer with a relatively even surface for supporting the support structure, to provide an even surface on which the capping assembly is laid down. It is preferred that the capping support layer is built up to form an even terrain of raised ground higher than the perimeter or rim of the landfill at ground level.

For reasons of good drainage of rainwater and/or removal of dirt and debris from the capping assembly, it is preferred that the surface of the capping support layer is not horizontally flat, but slopes down towards at least one point of the landfill perimeter, as discussed further hereinafter. The landfill and/or its capping support layer may be substantially mound-shaped, generally low mound-shaped.

The surface of the impermeable layer may include at least one elongate depression such as a furrow or channel, which is inclined along its length. Advantageously, the furrow or channel may act as a channel for drainage and/or to remove dirt and debris that passes into the general depressions on the undulating surface. Where the landfill and/or its capping support layer is sloping, the undulating surface may take the form of one or more channels or furrows inclined substantially down any slope. Each such elongate depression will preferably run downwards to a point on the perimeter of the site, or upwardly and then downwardly between two points on the perimeter of the site.

The site preferably has decomposing material and/or a capping support layer built up to form an even terrain of raised ground higher than the perimeter or rim of the site at ground level to enhance the complete drainage of rainwater and/or removal of dirt and debris from the capping assembly. It will be necessary to make the sides of the raised terrain fluid-impermeable. These however may fall away steeply, for example at about 45 degrees to the horizontal, so that it will not be possible to use the structure of the present capping assembly on these sides, as it will be impossible to lay down a stable support structure there.

In this case, the sides are covered with sheets of the solar power generating layer bonded together, for example by heat sealing, hot wedge or hot air welding, chemical fusion or adhesion, or fixed firmly together at the edges to form a fluid- proof seal, for example by fastening means, such as, preferably elongate, closures along a seam, for example, elongate clips, clasps or slides, or a plurality of staples. At the edge of the raised terrain, it is preferred that the edge portions of the sheets of the layer on the sides extend over or under and are conventionally bonded to the edge portions of the sheets of the layer on the top, for example the above methods. It is preferred that the upper surface of the solar power generating layer on those sides should bear no solar power generating means.

The capping assembly may cover the entire area of the site, typically of the order of hectares, to prevent infiltration of rainwater and collect decomposition gases.

The generating means favourably cover a large fraction of the area of the assembly, thereby providing an extensive area over which solar power can be generated, with an electricity generation capacity of the order of megawatts. On large sites the capping assembly may be added in stages, provided the rest of the site is covered with a gas impermeable layer and gas collection and/or flare-off means to seal decomposition gases away from the atmosphere. However, in view of the need to seal the edges, this will have to be done by sealing capping assembly modules to one another.

Advantageously, providing solar power generating means on an impermeable layer allows the impermeable layer to perform a dual role, sealing the decomposing material against the escape of gases to the atmosphere or against the influx of gas from the atmosphere, and generating solar power.

Advantageously, the impermeable layer facilitates capture of the gases (for example methane, hydrogen and carbon dioxide) produced by the decomposing waste material, for energy production. Where the installation is a silage clamp, the impermeable layer helps to seal fermenting silage against oxygen entering.

A further advantage is that the decomposing material can be sealed and the solar power generating means installed in a single procedure. A flexible sheet also has the advantage that it is capable of flexing with the sheets to which they are attached, so that the solar power generating layer may move up and down with varying sedimentation and compaction rates of landfill and dump sites, and the sheets may be rolled for transport and unrolled and used in the installation.

Such sheets may be used as sheet units of the solar generation layer, or may more usually bonded together at the edges in situ, for example by heat sealing, hot wedge or hot air welding, chemical fusion or adhesion, or fixed firmly together at the edges, preferably to form a significantly fluid-proof seal, for example by fastening means, such as, preferably elongate, closures along a seam, for example, elongate clips, clasps or slides, or a plurality of staples, to form sheet units of the solar power generating layer for installation.

The sheet units of the solar power generating layer are of a flexible fluid- impermeable material. It is important that the sheet material is weather and abrasion resistant. It may comprise one or more of

ethylene propylene diene terpolymer (EPDM); high density polyethylene (HDPE); flexible polypropylene (fPP), reinforced fPP-R; polyvinyl chloride (PVC); thermoplastics polyolefin, including linear low-density polyethylene (LLDPE) and medium-density polyethylene (MDPE);

polyester reinforced thermoplastics polyolefin material;

polyurea, polyamide and polytetrafluoroethylene (PTFE); and

glass and bitumen-impregnated non-woven geotextile.

As noted in the definition above, the solar power generating layer may conveniently be made up of component sheet units, each of which is often made up of a number of component sheets, for example of 2m x 5.8m. Such sheets are commercially available, and are usually elongate and supplied in the form of a roll. Individual smaller sheets are welded or adhered together to form a larger sheet, for example of 2 m x 12 m or larger still. It is advantageous if substantially all the sheets are of the same size, and are laid from the rolls end to end and side by side in a grid array.

These larger sheets may be formed into a roll for transport and ease of handling, and may then be used as sheet units of the solar power generating layer and rolled out over the site and welded or adhered together in order to cover the entire or portions of a landfill site.

Generally, however, these larger sheets are joined on site to form even larger sheets of for example 50m x 50m, each of which is used as a sheet unit of the solar power generation layer, held in position in relation to adjacent similar sheet units by having their edges bonded together in situ, for example by heat sealing, hot wedge or hot air welding, chemical fusion or adhesion, or fixed firmly together to form a fluid-proof seal, for example by fastening means, such as, preferably elongate, closures along a seam, for example, elongate clips, clasps or slides, or a plurality of staples. It is important that the solar power generating means is weather and abrasion resistant. The solar power generating means may thus suitably comprise flexible thin-film solar photovoltaic cells. Advantageously, flexible thin-film solar photovoltaic cells are relatively lightweight and inexpensive, can be mass- produced and are suitable for covering large areas as employed in Building Integrated Photovoltaics (BIPV) and Building Applied Photovoltaics (BAPV). A further advantage is that thin-film solar photovoltaic cells are sufficiently flexible to be capable of flexing with the sheets to which they are attached, so that the solar power generating layer may move up and down with varying sedimentation and compaction rates of landfill and dump sites, and the sheets may be rolled for transport and unrolled and used in the installation.

Individual solar photovoltaic cells may be attached to a component sheet, for example of 2m x 5.8m, bearing 4 solar photovoltaic cells, with the photovoltaic cells electrically connected together.

The thin-film solar photovoltaic cells may be thin-film solar photovoltaic cells comprising amorphous silicon or polycrystalline materials such as nano- crystalline silicon, protocrystalline silicon, cadmium telluride (CdTe), and copper indium gallium selenide (CIS, CIGS); or they may be printed semiconductor thin- film photovoltaic cells.

The sheet units of the solar power generating layer may be laid directly on top of the support structure with the solar photovoltaic cells facing upwards, but preferably the surface of the support structure is covered by a protective layer of sheets units. The protective layer protects any heat welds or areas of adhesive between any component sheets of the sheet units of the solar power generating layer from abrasion or other deleterious action of the support structure in contact with the underside of the solar power generating layer. The sheets of the protective layer may be of a low cost plastics material, generally less substantial or biodegradable (thinner and less costly) than a geomembrane as used traditionally in landfill applications. Rather, such protective layers are more typically used in agriculture or building. The objective here is low cost.

Such protective layers may comprise one or more plastics including polypropylene, polystyrene, acrylonitrile butadiene styrene, polyethylene terephthalate, polyester, polyamides, polyvinyl chloride, polyurethanes, polyvinylidene chloride, polyethylene, polytetrafluoroethylene or other plastics or polyolefin, polyurea, polyamide and polypropylene. The installation is preferably provided with conventional plastics or metal porous or perforated vertical riser shaft gas collection pipes or drill casings running through the capping assembly into the decomposing material. These capture a significant proportion of the gases (for example methane, hydrogen and carbon dioxide, hydrogen) produced by the decomposing waste material, for energy production, usually electricity generation.

The gas collection pipes or drill casings may also be complemented by horizontal landfill gas collection pipes placed into trenches within the landfill mass and covered with earth or sand or landfill material prior to final capping with a capping assembly of the present invention.

Each solar cap may be provided with gas collection means to deal with the gases (for example methane, hydrogen and carbon dioxide) that accumulate under it. Each solar cap may be provided with at least one upright porous or perforated metal or plastics pipe running through the solar power generating layer into the support structure, but optionally not passing beyond the latter. In particular, one such 'peak' porous or perforated metal or plastics pipe may be provided at or near the highest point of the solar cap. Optionally, in a rectangular solar cap, an upright 'midpoint' pipe may be provided at or near the midpoint of the most direct slope down to each of the surrounding holding means and/or near the midpoint of the slope down to the corners of the solar cap.

All these porous or perforated metal or plastics pipes capture the gases from the decomposing material. Preferably any midpoint pipes communicate with the peak porous or perforated metal or plastics pipe, and it is in turn fitted with a take-off pipe through which the gases are taken off to be used, typically for energy production, typically electricity or heat generation. For reasons of safety, any take-off pipe is preferably fitted with a back-flow preventer, such as a non-return valve. Each peak drill casing is preferably fitted at or near its upper end with a pressure-sensitive gas release and flare-off device. In the event of the device detecting gas overpressure above a preset safe value beneath the solar cap on which it is mounted, it vents gas into the atmosphere and may desirably ignite such gases, usually with an electric spark. Such gas collection means are described further hereinafter in relation to the second preferred embodiment of the first aspect of the present invention

In a first preferred embodiment of the second aspect of the present invention, there is provided a method for constructing an installation for generating solar power, which comprises constructing a capping assembly over a mass of decomposing material comprising the steps of

constructing a support structure which comprises at least two man-made mounds and

covering it with a fluid-impermeable flexible sheet material, where said sheet material has solar power generating means bonded thereto, or the method comprises the further step of bonding said solar power generating means to the sheet material. .

The support structure may (less usually) be constructed on the surface of the decomposing material (typically in a landfill). In general, the decomposing material is covered over with a capping support layer, including for example clay, earth, ash, and/or other particulate material, and may be produced by using earth-moving equipment to position such materials. The support structure is constructed on the capping support layer.

Preferably the surface of the decomposing material is first covered with a capping support layer with a relatively even surface to provide an even surface on which the capping assembly is laid down. It is preferred that the capping support layer is built up to form an even terrain of raised ground higher than the perimeter or rim of the landfill at ground level.

The present capping assembly may be retrofitted to an existing site, in particular a landfill or dump site. These will often be made up of decomposing material heaped into a plateau higher than the perimeter of the site, with an uneven surface. Depending on how uneven the surface is, it may be preferred to partially level the surface before applying and evening out a capping support layer. The mounds may each be constructed to be a hillock or hummock or they may be constructed to be elongate ridges, in each case with elongate depressions between them, the side walls of which are formed by the sheet units of the solar power generating layer.

The depth of the depressions will depend on the angle to the horizontal of the side walls, and at lower angles, they will be relatively shallow. The desired angle from the horizontal of the side walls, and the stability of the surface slope of a heap or pile of any given material at that angle will determine the materials used in the mounds.

The mounds may be produced by using earth-moving equipment to position such materials as gravel, rock, ash, clay and soil. Alternatively, the mounds may be produced by placing boulders or rounded and/or porous structures made or metal, wood, plastic, concrete or any other like material on the surface of the capping support layer.

In a preferred form of this embodiment of the invention, each mound is constructed to comprise a continuous or discontinuous layer of boulders and/or gravel, which may have a mean size of >1cm in diameter, for example >20cm in diameter, >50cm in diameter or >100cm in diameter. The interstitial spaces between the boulders or gravel allow for relatively unimpeded gas permeation through the capping assembly. This situation differs significantly from the remainder of the compressed mass of waste material which is far from uniform or easily permeable to landfill gases.

Preferably, at least a portion of each mound surface is constructed to have a slope of at least 5 degrees to the horizontal, more preferably, at least 15 degrees to the horizontal, in particular at least 25 degrees to the horizontal. These angles may be measured in any direction on the surface of the capping assembly, but especially in the direction of greatest slope.

Favourably, the support structure comprises a series of mounds, separated by elongate depressions, such as furrows or channels. Such mounds may generally be constructed in a rectangular grid pattern, so that at least a portion of the solar power generating layer is undulating. The mounds are produced on the surface of the capping support layer prior to laying down the solar generation layer on the capping support layer, so as to introduce mounds and undulations beneath the layer. The solar generation layer then rises and falls over the mounds and depressions, forming a 'solar cap' over each mound, the sloping walls of the solar caps defining the side walls of the elongate depressions in the capping assembly.

The method for constructing an installation for generating solar power, comprising constructing a capping assembly over a mass of decomposing material may thus comprise the steps of

constructing a support structure in the form of an undulating surface above the decomposing material, and

covering it with a substantially gas-impermeable flexible sheet material, wherein said sheet material has solar power generating means bonded thereto.

The bottom of the depressions may be constructed to be relatively flat and/or broad, so that they may be advantageously used to provide access thoroughfares, such as pathways or walkways between the solar caps, for example for inspection and maintenance.

Preferably the assembly is so constructed that each such elongate depression will run to a point on the perimeter of the site, and more preferably each runs between two points on the perimeter of the site. Any capping support layer may in particular be so constructed that each elongate depression is aligned down at least one downwardly sloping surface towards the perimeter of the installation, or upwardly and then downwardly between two points on the perimeter of the site.

The site is preferably constructed with the decomposing material and/or a capping support layer built up to form an even terrain of raised ground higher than the perimeter or rim of the site at ground level. It may be necessary to make the sides of the raised terrain fall away steeply, for example at about 45 degrees to the horizontal.

The surface of the support structure may then be covered by a protective layer comprising a number of sheet units. These sheet units are typically bonded together at the edges, for example by heat sealing, hot wedge or hot air welding, chemical fusion or adhesion, or fixed firmly together at the edges, preferably to form a significantly fluid-proof seal, for example by fastening means, such as, preferably elongate, closures along a seam, for example, elongate clips, clasps or slides, or a plurality of staples.

Alternatively, a number of smaller sheets may be laid over the support structure and bonded or fixed firmly together at the edges in situ, for example by the above methods, to form a number of sheet units which are then in turn bonded together in situ, for example by the above methods.

Where the capping support layer forms a terrain raised above the perimeter of the installation, its sides are also covered with sheet units of the protective layer bonded together at the edges and bonded to the edge portions of the sheet units of the layer on the top, for example by the above methods.

The surface of the support structure or the protective layer may then be covered by the solar power generating layer, or a precursor thereof without solar power generating means, comprising a number of sheet units, which are typically laid over the support structure and bonded together at the edges, for example by heat sealing, hot wedge or hot air welding, chemical fusion or adhesion, or fixed firmly together at the edges to form a fluid-proof seal, for example by fastening means, such as, preferably elongate, closures along a seam, for example, elongate clips, clasps or slides.

More usually, a number of smaller sheets are bonded together in situ, for example by the above methods, to form sheet units of the solar power generating layer for installation. Individual component sheets, for example of 2m x 5.8m, may bear attached solar photovoltaic cells, for example four such cells, with the photovoltaic cells electrically connected together, which are then bonded together at the edges in situ to form a number of sheet units which are then in turn bonded together in situ, all for example by the above methods. Alternatively, precursor sheet units or component sheets may be similarly installed, and a solar power generating layer made up from a precursor layer, sheet unit or sheet by attaching solar power generating means to it in situ. Where the means comprise or consist of a number of flexible thin-film solar photovoltaic cells, for example comprising amorphous silicon or polycrystalline materials such as nano-crystalline silicon, protocrystalline silicon, cadmium telluride (CdTe), and copper indium gallium selenide (CIS, CIGS); or printed semiconductor thin-film photovoltaic cells, the solar power generating means may be adhered to the relevant substrate under pressure using a specialized heat- melt adhesive, as described hereinbelow in relation to the Figures.

Where the capping support layer forms a terrain raised above the perimeter of the installation, its sides are also covered with sheet units of the solar power generating layer bonded together at the edges and bonded to the edge portions of the sheet units of the layer on the top, all for example by heat sealing, hot wedge or hot air welding, chemical fusion or adhesion, or fixed firmly together at the edges, preferably to form a significantly fluid-proof seal, for example by fastening means, such as, preferably elongate, closures along a seam, for example, elongate clips, clasps or slides, or a plurality of staples.

According to a second preferred embodiment of the first aspect of the present invention, there is provided an installation for generating solar power, comprising: a mass of decomposing material; and;

a capping assembly, comprising

an optional base layer above the decomposing material, comprising a plurality of flexible sheet units of a fluid impermeable material, and

a solar power generating layer above the base layer, comprising a plurality of sheet units of a flexible fluid impermeable material with solar power generating means bonded thereto for producing electric power from sunlight incident on at least a portion of the installation,

wherein

in the base layer, if present, the edge portions of neighbouring sheet units are adjacent and held together by the weight of an overburden above the edge portions to form a partially fluid-impermeable base layer, and in the solar power generating layer, the edge portions of neighbouring sheet units are adjacent and held together by the weight of a holding means above the edge portions to form a substantially fluid-impermeable solar power generating layer. For the avoidance of doubt, there is no restriction on the size of the fluid impermeable sheet units of the solar power generating layer.

Each sheet unit may be a sheet as supplied from the manufacturer, with solar power generating means attached to if, or it may be made up by attaching solar power generating means to it in situ. Each sheet unit may comprise or consist of a number of such sheets welded or adhered together.

As described hereinbelow, it is preferred that each sheet unit is a relatively large fluid-impermeable sheet unit comprising a number of smaller sheets bonded together at the edges, for example by heat sealing, hot wedge or hot air welding, chemical fusion or adhesion, or fixed firmly together at the edges to form a fluid- proof seal, for example by fastening means, such as, preferably elongate, closures along a seam, for example, elongate clips, clasps or slides. Although the component sheet units of the solar power generating layer are fluid impermeable, the layer itself may be significantly fluid permeable, depending in the quality of the holding means. It is preferred that the layer is fluid- impermeable. Advantageously, holding the sheet units in the respective layers together with an overburden or a holding means avoids the time consuming process and cost of: meticulously aligning the sheet units with each other and heat welding or adhering them together. Thus, the decomposing material can be sealed and the solar power generating means installed in a simpler, cheaper process than hitherto.

Although the installation may be a new site constructed ab initio, a main advantage is that the present invention also provides a simpler, cheaper process than hitherto for retrofitting a capping assembly to existing uncapped sites to render them safer and to use them as a source of both gas fuelled and solar energy. The invention also enables previously capped sites that are already equipped for the recovery of landfill gases, but without a solar power generating layer of the present invention, to be retrofitted with such a solar power generating layer. It is preferred that the base layer is present. The flexible sheet units of the base layer are generally made up as sheets at the source of supply, stored and transported conveniently as a roll, which can be unrolled on-site as sheet units and quickly and inexpensively held down and together with overburden in order to cover the entire or portions of a landfill site. Optionally, such base layer sheets can be fused to from larger sheets units of 5m x 20m, and those sheet units held down and together with overburden in order to cover the entire or portions of a landfill site.

For the sheet units of the solar power generating layer, individual solar photovoltaic cells may be attached to a smaller sheet, for example of 2m x 5.8m, bearing 4 solar photovoltaic cells, with the photovoltaic cells electrically connected together, and individual smaller sheets are welded or adhered together to form a larger sheet, for example of 2 m x 12 m or larger still. These larger sheets may be formed into a roll for transport and ease of handling, and may then be used as sheet units of the solar power generating layer and rolled out over the site and held down and together in order to cover the entire or portions of a landfill site quickly and less expensively.

Generally, however, these larger sheets are joined on site to form even larger impermeable sheets of for example 50m x 50m, each of which is used as a sheet unit of the solar power generation layer, held in position in relation to adjacent similar sheet units by a holding means.

It is clearly desirable that, where the edge portions of the sheet units of the solar power generating layer pass under the holding means, the upper surface of the sheet units in those edge portions should bear no solar power generating means.

As described further hereinbelow, the holding means on the solar power generating layer may be advantageously used to provide access thoroughfares, such as pathways, walkways, tracks, lanes, and even roadways, between areas of the solar layer, for example for inspection and maintenance. The holding means may additionally or alternatively provide channels, gutters, troughs and even watercourses for drainage, especially in areas of high rainfall such as the tropical and equatorial zones, and even temperate western maritime zones.

The edge portions of neighbouring sheet units in the base layer being adjacent and held together only by an overburden above the respective edge portions means that the base layer will not be a totally fluid impermeable layer. The sheet units of the base layer may be of a geomembrane material, and may be composed of one or more of

ethylene propylene diene terpolymer (EPDM); high density polyethylene (HDPE); flexible polypropylene (fPP), reinforced fPP-R; polyvinyl chloride (PVC);

thermoplastics polyolefin, includng linear low-density polyethylene (LLDPE) and medium-density polyethylene (MDPE);

polyurea, polyamide and polytetrafluoroethylene (PTFE);

glass and bitumen-impregnated non-woven geotextile, or

polyester reinforced thermoplastics polyolefin material. The sheet units of the base layer may be laid down or constructed directly on top of the site decomposing material, but preferably the surface of the material is covered with a capping support layer with a relatively even surface for supporting the base layer, to provide an even surface on which the capping assembly is laid down. It is preferred that the capping support layer is built up to form an even terrain of raised ground higher than the perimeter or rim of the site at ground level.

The present capping assembly may be retrofitted to an existing site, in particular a landfill or dump site. These will often be made up of decomposing material heaped into a plateau higher than the perimeter of the site, with an uneven surface. Depending on how uneven the surface is, it may be preferred to partially level the surface before applying and evening out the capping support layer.

Advantageously, a capping support layer may also reduce damage to the base layer by providing a smoother surface for supporting the base layer. The capping support layer may comprise one or more of gravel, rock, ash, clay, and/or soil. For reasons of good drainage of rainwater and/or removal of dirt and debris from the capping assembly, it is preferred that the surface of the capping support layer is not horizontally flat, but slopes down towards at least one point of the landfill perimeter, as discussed further hereinafter.

The sheet units of the base layer lie on the upper surface of the decomposing material, or preferably on the upper surface of a capping support layer. The edges of neighbouring sheet units may be near, abutting or, preferably, overlapping each other by 1 to 500cm, for example 10 to 200 cm, preferably 20 to 50 cm. The closer the edges of the sheet units of the base layer or the greater the area of overlap, the greater is the degree of impermeability of the layer, i.e. of adjacent sheet units that are not heat-sealed or adhered together.

As mentioned above, the base layer sheet units (often geomembrane sheets) are usually elongate and supplied in the form of a roll. It is convenient if substantially all the sheet units are of the same size, and are laid from the rolls end to end and side by side in a grid array.

The overburden may be of any materials that are sufficiently dense, and be of sufficient thickness to hold the edges of the sheet units of the base layer down and together. Often the overburden may comprise mineral material, such as one of more of gravel, rock, ash, clay, boulders and soil.

In a preferred embodiment of the invention, the overburden comprises a continuous or discontinuous layer of boulders and/or gravel, which .may have a mean size of >1cm in diameter, for example >20cm in diameter, >50cm in diameter or > 100cm in diameter. The interstitial spaces between the boulders or gravel allow for relatively unimpeded gas permeation through the capping assembly. This situation differs significantly from the remainder of the compressed mass of waste material which is far from uniform or easily permeable to landfill gases. In this manner, landfill gases that have escaped from the non-sealed base layer geomembranes can make their way more easily to the underside of the solar power generating layer above the base layer, and can be reliably extracted at specific points from the waste material housed in the installation.

The overburden often comprises in ascending order a layer of sand or earth on the base layer, a layer of boulders and/or gravel, and then a layer of earth or clay. To save installation time, the overburden conveniently extends not only over the adjacent edges of the component sheet units of the base layer, but over the majority of the base layer, especially over significantly all the layer.

The minimum thickness of the overburden, depending on the materials used, may be 10 cm to 200 cm, preferably from 40 cm to 80 cm.

Alternatively, at points where the holding means lies above the base, it is possible to reduce the thickness and/or density of the overburden, for example by reducing the number of, or omitting, boulders or gravel if present, as the combined weight of the overburden and holding means is adequate to hold the both layers in place.

The installation is preferably provided with conventional plastics or metal porous or perforated vertical riser shaft gas collection pipes or drill casings running through the capping assembly into the decomposing material. These capture a significant proportion of the gases (for example methane, hydrogen and carbon dioxide) produced by the decomposing waste material, for energy production, usually electricity generation. The pipes or casings may also be complemented by horizontal landfill gas collection pipes placed into trenches within the landfill mass and covered with earth, clay or sand or landfill material prior to final capping with a capping assembly of the present invention. The proportion or partial pressure of the gases that leak through the base layer relative to the partial gas pressure of gases below the base layer will depend on a number of factors. Where the installation is (preferably) provided with plastics or metal porous or perforated vertical riser shaft gas collection pipes or drill casings to extract gases from the decomposing material, such factors include the bores, pump-off rates and area density of vertical riser shaft gas collection pipes or drill casings relative to the volume of gas produced by the decomposing material.

The degree of adjacency of the component sheet units of the base layer is also one such factor. It is preferred that the edge portions of the sheet units overlap, as that will tend to decrease the degree of leakage compared with the edge portions abutting or being close. The size of the overlap will also influence the efficiency of retaining landfill gases by the overlapping base layer sheet units.

Where the edge portions of the sheet units overlap, the pressure that is applied by the overburden that is borne by the overlap will influence how efficient the restrictive barrier formed by the overlapping sheet units will be. However, at all times gases will escape between the non-sealed base layer sheet units. Any proportion of the gas that seeps through the base layer is captured by the solar power generating layer and the holding means.

Preferably, the holding means on the solar power generating layer not only holds adjacent sheet units together but forms a fluid impermeable seal between the fluid impermeable sheet units of the solar power generating layer.

The sheet units of the solar power generating layer are of a flexible fluid impermeable material. It is important that the sheet material is weather and abrasion resistant, and it may comprise one or more of

thermoplastics polyolefin, including linear low-density polyethylene (LLDPE) and medium-density polyethylene ( DPE);

polyester reinforced thermoplastics polyolefin material;

polyurea, polyamide and polytetrafluoroethylene (PTFE); and glass and bitumen-impregnated non-woven geotextile.

It is important that the solar power generating means is weather and abrasion resistant. The solar power generating means may thus comprise flexible thin-film solar photovoltaic cells. Advantageously, flexible thin-film solar photovoltaic cells are relatively lightweight and inexpensive, can be mass-produced and are suitable for covering large areas as employed in Building Integrated Photovoltaics (BIPV) and Building Applied Photovoltaics (BAPV). A further advantage is that thin-film solar photovoltaic cells are sufficiently flexible to be capable of flexing with the sheets to which they are attached, so that the sheets may be rolled for transport and unrolled and used as sheet units of the solar generation layer. More usually, such sheets are bonded together in situ, for example by heat sealing, hot wedge or hot air welding, chemical fusion or adhesion, or fixed firmly together at the edges to form a fluid-proof seal, for example by fastening means, such as, preferably elongate, closures along a seam, for example, elongate clips, clasps or slides, to form sheet units of the solar power generating layer for installation. Importantly the solar power generating layer may move up and down with varying sedimentation and compaction rates of landfill and dump sites.

The solar power generating layer may be formed by bonding the thin-film power generating means (for example, thin-film amorphous silicon solar laminates available from United Solar Ovonic) onto a fluid-impermeable sheet with an adhesive. The sheet may be, for example a single-ply PVC membrane (such as one available from Sika Sarnafil), and bonding may be effected using, for example a heat-melt adhesive. The sheet units of the solar power generating layer may be laid directly on top of the overburden with the solar photovoltaic cells facing upwards, but preferably the surface of the overburden is covered by a protective layer of adjacent sheets. Such a protective layer protects any heat welds or areas of adhesive between any component sheets of the sheet units of the solar power generating layer from abrasion or other deleterious action of the overburden in contact with the underside of the solar power generating layer from, for example, dirt, earth or sand from interfering with the integrity of the heat seal or adhesive employed between component sheets of the sheet units of the solar power generating layer.

The sheets of the protective layer may be of a low cost plastics material, and may be considerably less substantial or biodegradable (thinner and less costly) than a geomembrane as used traditionally in landfill applications. Rather, such protective layers are more typically used in agriculture or building. The objective here is low cost.

Such protective layers may comprise one or more plastics including polypropylene, polystyrene, acrylonitrile butadiene styrene, polyethylene terephthalate, polyester, polyamides, polyvinyl chloride, polyurethanes, polyvinylidene chloride, polyethylene, polytetrafluoroethylene or other plastics or polyolefin, polyurea, polyamide and polypropylene.

The edges of neighbouring sheet units of the solar power generating layer may be near, abutting or, preferably, overlapping each other by 10 to 500 cm, preferably 30 to 50 cm.

As mentioned above, solar power generating layer component sheets are usually elongate and supplied in the form of a roll. It is convenient if substantially all the sheets are of the same size, and are laid from the rolls end to end and side by side in a grid array. These component sheets may be used as sheet units of the solar power generating layer, but preferably their edges are bonded together in situ to form sheet units, for example of about 50 m x 50 m, for example by heat sealing, hot wedge or hot air welding, chemical fusion or adhesion, or fixed firmly together to form a fluid-proof seal, for example by fastening means, such as, preferably elongate, closures along a seam, for example, elongate clips, clasps or slides.

When a protective layer is present, the sheets of the protective layer are often adjacent (as herein defined). It is then often convenient for at least some of these areas to be in register with the areas where the sheet units of the solar power generating layer are adjacent, so that the edge portions of neighbouring sheets and sheet units in each respective layer that are adjacent are held together by the weight of the same holding means. Protective layer sheets are usually elongate and supplied in the form of a roll. It is convenient if substantially all the sheets are of the same size, and are laid from the rolls end to end and side by side in a grid array.

The holding means is preferably so dimensioned that it overlaps and extends significantly beyond the area of adjacency (i.e. closeness, abutment or overlap) of neighbouring sheet units of the solar power generating layer (and optionally of the protecting layer).

It may extend between 50 cm and 600 cm in each direction beyond and at right angles to the edges of the adjacent sheet units, and is preferred that it extends 100 cm to 300 cm from the edges.

As noted above, the edges of neighbouring sheet units of the solar power generating layer may be near, abutting or, preferably, overlapping each other by 10 to 100 cm, preferably 10 to 40 cm.

The areas of the solar power generating layer over which the holding means extends should preferably be free of any solar power generating means, such as solar photovoltaic cells. The structure, dimensions and material will depend on the additional uses to which the holding means is to be put. Thus, if it is to form a lower part of a channel, gutter, trough or watercourse only for drainage, it will generally need to bear less maximum pressure than if it is to form part of a thoroughfare, for example for inspection and maintenance. If it is to form part of pedestrian access such as a pathway or walkway, it will generally need to bear less maximum pressure than if it is to form part of a track, lane or roadway for vehicles. Thoroughfares may of course also act as drains. For all such uses, the holding means preferably comprises an upper part overlying a lower part, the upper part often being roughly coterminous with or extending beyond the edges of the lower part, and the two parts sandwich and squeeze together the area of adjacency of two neighbouring sheet units of the solar power generating layer (and optionally any protective layer) between them.

Where the upper part of the holding means forms a pathway or roadway, it may be 0.5m to 5m wide.

It is preferred that a protective layer is present and is also sandwiched by the two parts of the holding means, so that it serves to protect the solar power generating layer from abrasion or other deleterious action of the lower part in contact with the underside of the solar power generating layer.

The lower part of the holding means may rest on ari often coterminous laminar support layer.

In an alternative embodiment, the edges of the protective layer may pass under the lower part of the holding means or the support layer (if present) and be sandwiched against the overburden or the support layer (if present).

Preferably, the holding means on the solar power generating layer not only holds neighbouring sheet units together but forms a fluid impermeable seal between sheet units. Often the holding means will comprise one laminar structure, and preferably two forming a sandwich as mentioned above.

The holding means may be of any materials that are sufficiently dense, and of sufficient thickness to hold the edges of the sheet units of the solar power generating layer and any protective layer down and together, and

have sufficient compressive and flexional strength to bear the maximum pressure that will be placed on them in use.

The material of the holding means may be capable of adhering to the solar power generating layer. Depending on the use to which the holding means will be put, it may be a laminar structure comprising a layer of asphalt rubber, and it preferably comprises an upper and a lower layer of asphalt rubber forming a sandwich about the edges of the sheet units of the solar power generating layer and any protective layer.

In addition such asphalt rubbers may vary as a function of the crumb size of the rubber employed and the modifiers employed including elastomer and plastomer modified asphalt rubber.

An advantage of an asphalt rubber as a component of the holding means, and in particular a holding means sandwich is to flex with weather changes and varying landfill or dump site sedimentation and compaction rates. Here flexing refers specifically to resisting permanent deformation and / or affording increased elasticity and resistance to sheering, i.e. when compared to others composites, concretes and asphalts. The skilled person will be aware that crumb rubber binders are not all the same. They can satisfy different standards and requirements by changing production parameters and raw material ingredients, such as asphalt, rubber and additives.

The skilled person will also be aware that the addition of varying quantities of elastomers, such as SBS - Poly(Styrene Butadiene Styrene), SEBS - Poly(Styrene-Ethylene-Butadiene-Styrene) and / or/ plastomers, such as APP - atactic polypropylene allow for the asphalt rubber to be more waterproofing and/or impermeable. This feature is critical in the absence of a continuous sealed base layer in the capping asssembly of the present invention on a landfill or dump site. Furthermore, the crumbed rubber advantageously improves the asphalt's binding qualities, i.e. to provide its function as a holding means, preferably as a sandwich for the solar power generating layer, and the need to thereby capture landfill gases.

The rubber asphalt layers (upper and lower) can be laid down at a thickness of 1 cm to 20 cm, but preferably in the range of 2cm to 4 cm for each of the upper and lower layers of the holding means sandwich. Less desirably other composites can be employed. These include mineral material, such as one or more of gravel, rock, ash, clinker, sand and earth, for example in the form of a concrete or compacted hardcore aggregate, or a composite bound together with bitumen. If it is a concrete, it may be laid down as flags, optionally cemented together, or cast in situ.

However, these latter (concrete) materials are less preferred, in particular for installations in which the decomposing material is still settling and compacting, because of their relative inflexibility for the intended application. This will however not necessarily render their use inappropriate depending upon the age of the landfill or dump site and the extent of its compaction. These may also be present as a sandwich at a thickness of 1 cm to 20 cm, but preferably in the range of 2cm to 4 cm for each of the upper and lower layers of the holding means sandwich.

The upper part of the holding means is preferably liquid impermeable to minimise the access of rainwater to the landfill. The preferred composition of the upper part of the holding means comprises or is an asphalt rubber,

Often the lower part of a two part holding means sandwich is let into the upper face of the overburden. The lower part of the holding means may rest on an often coterminous laminar support layer of compacted hardcore aggregate,

In one form of this embodiment of the invention, the lower part of a holding means sandwich extends beyond the edge portions of adjacent sheet units under a part or all the solar power generating layer. It is preferred that any such lower part is of a flexible material, such as an asphalt rubber as hereinabove described for the holding means, so that it may flex with the solar power generating layer as the landfill material compacts. In this form the base layer may be omitted, and the overburden laid directly on the decomposing material in the landfill.

Where any sheet unit comprises component sheets adhered or welded together, and it would be desirable to have an underlying protective layer, the extended lower part of the holding means ('holding means extension') may serve that purpose, and a protective layer may be dispensed with.

Accordingly in another form of the second preferred embodiment of the first aspect of the present invention, there is provided an installation for generating solar power, comprising:

a mass of decomposing material; and

a capping assembly, comprising

optionally, a base layer above the decomposing material, comprising a plurality of flexible sheet units of a fluid impermeable material, and

wherein

in the base layer, if present, the edge portions of neighbouring sheet units are adjacent and held together by the weight of an overburden above the edge portions to form a partially fluid-impermeable base layer, and

in the solar power generating layer, the edge portions of neighbouring sheet units are adjacent and held together by the weight of a the upper part of a holding means above the edge portions to form a substantially fluid-impermeable solar power generating layer, and

the lower part of the holding means extends under a part or all of the solar power generating layer.

Preferably, in such an installation, the lower part of the holding means is fluid impermeable. More preferably, the lower part of the holding means comprises a rubber asphalt. In such an installation, the solar power generating layer may conform to the capping support layer, or to the top of the decomposing material, if there is no capping support layer. Preferably, at least a portion of the support structure is substantially undulating. It then comprises a series of mounds, each bearing part of the solar power generating layer as a solar cap (as defined hereinbelow), and separated by elongate depressions, the bottoms of which are defined by elongate upper parts of the holding means.

Substantially all the edge portions of the sheet units of the solar power generating layer, and the protective layer if present, may be held down and together by holding means as described above. Where they form a grid array of rectangular or square sheet units, the holding means will form a corresponding grid of intersecting elongate holding means, each running along the edges of the solar power generating layer sheet units that it holds together. Some or all of the holding means may run from one side of the site to the other.

As noted above, the sheet units, in particular large, square sheet units, are usually formed from component sheets. These component sheets are usually elongate and supplied in the form of a roll, and laid from the rolls end to end and side by side in a grid array, and preferably have their edges bonded together in situ to form square sheet units, for example of a preferred size of about 50 m x 50 m, as per a preferred size of a 'solar cap', as discussed further hereinbelow, for example by heat sealing, hot wedge or hot air welding, chemical fusion or adhesion, or fixed firmly together at the edges to form a fluid-proof seal, for example by fastening means, such as, preferably elongate, closures along a seam, for example, elongate clips, clasps or slides. The capping assembly should capture substantially all gas leaking through the partially fluid- impermeable base layer, but the fluid-permeable overburden holds the fluid-impermeable solar power generating layer away from the base layer. Therefore, at the edges of the capping assembly (which may often be the edges of the site) the overburden should be omitted from between the edge portions of the sheets of the base and solar power generating layers. These edge portions should then be overlapped and bonded together, for example by heat sealing, hot wedge or hot air welding, chemical fusion or adhesion, or fixed firmly together at the edges to form a fluid-proof seal, for example by fastening means, such as, preferably elongate, closures along a seam, for example, elongate clips, clasps or slides, as per the conventional process for those skilled in the art..

Where the site has decomposing material and/or a capping support layer built up to form an even terrain of raised ground higher than the perimeter or rim of the site at ground level, it will be necessary to make the sides of the raised terrain fluid-impermeable.

These sides however may fall away steeply, for example at about 45 degrees to the horizontal, so that it will not be possible to use the structure of the present capping assembly on these sides, as it will be impossible to lay down a stable overburden. In this case, the sides are covered with sheets of the same base layer conventionally bonded together at the edges, for example by heat sealing, hot wedge or hot air welding, chemical fusion or adhesion, or fixed firmly together at the edges to form a fluid-proof seal, for example by fastening means, such as, preferably elongate, closures along a seam, for example, elongate clips, clasps or slides, or a plurality of staples.

At the edge of the raised terrain, it is preferred that the edge portions of the sheets of the base layer on the sides extend over or under and are conventionally bonded to the edge portions of the sheets of the base layer on the top, or vice versa, for example by the above methods.

Similarly, to complete the fluid-impermeable seal provided by the solar power generating layer, it is preferred that at least the edge portions of the solar power generating layer extend over the edge of the raised terrain to overlap and be conventionally bonded to the base layer on the sides, for example by the above methods. It may be preferred that the solar power generating layer extends over and is conventionally bonded to all or some of the base layer on the sides, for example by the above methods. The capping assembly may cover the entire area of the site, typically of the order of hectares, to prevent infiltration of rainwater and collect decomposition gases. The generating means, such as thin-film solar photovoltaic cells preferably cover a large fraction of the area of the assembly, thereby providing an extensive area over which solar power can be generated, with an electricity generation capacity of the order of megawatts.

On large sites the capping assembly may be added in stages, provided the rest of the site is covered with a gas impermeable layer and gas collection and/or flare-off means to seal decomposition gases away from the atmosphere. However, in view of the need to seal the edges, this will have to be done by sealing capping assembly modules to one another.

At least a portion of the outer surface of the solar power generating layer between at least some, and preferably substantially all, of the holding means is preferably inclined at an angle to the horizontal, thus forming inclined side walls on each side of the relevant holding means. This may be conveniently achieved by supporting each sheet unit in the relevant portion of the solar power generating layer on a support structure.

Accordingly, in another form of this preferred embodiment, described further below, a support structure which comprises at least two man-made mounds (as defined hereinbefore) is formed on the overburden or the overburden is formed into such a support structure.

The support structure raises the sheet material and solar power generating means. Advantageously, this renders the solar power generating means less prone to damage. The surface of each mound is sloping, so that any rainwater, soil, dirt or debris will be swept downhill under the influence of gravity, wind and rain, which reduces the formation or puddles or accumulation of dirt or debris. Such accumulation may otherwise occur on a level installation surface and

reduce the power generating efficiency of the solar power generating means, lead to an increased risk of transmission of diseases such as yellow fever and malaria, and/or impair access to the solar power generating means, for example for maintenance.

Preferably, at least a portion of the support structure for the solar power generating layer comprises a plurality of mounds between the holding means for the solar power generating layer, so that the solar power generating layer undulates to form a plurality of solar caps with peaks. The layer of boulders and/or gravel in the preferred overburden thus affords increased gas permeability so that landfill gases that have escaped from the non-sealed base layer can make their way more easily to the peak regions of the solar caps, and that can be more readily and reliably collected than via the hit and miss approach of drilling into the compacted waste.

Substantially all the outer surface of the side walls of the solar power generating layer which bear solar power generating means may be at an angle of at least 3 degrees to the horizontal. At least a portion of the outer surface of the side walls of the solar power generating layer which bear solar power generating means may be at an angle of at least 15 degrees to the horizontal. At least a portion of the outer surface of the side walls of the solar power generating layer which bear solar power generating means may be at an angle of at least 25 degrees to the horizontal. These angles may be measured in any direction on the surface of the capping assembly, but preferably at right angles to the long axis of at least one elongate holding means. Depending on the dimensions of the solar power generating layer sheet units, the mounds may each be a hillock or hummock or they may be elongate ridges, in each case with elongate depressions or furrows between them, the bottoms of which are defined by the holding means, and the side walls of which are formed by the sheet units of the solar power generating layer.

The depth of the depressions will depend on the angle to the horizontal of the side walls, and at lower angles, they will be relatively shallow.

In one embodiment of the invention, the surface of the capping assembly will thus comprise a plurality of elongate depressions, generally in a rectangular grid pattern, so that the surface of the capping assembly is undulating. The solar power generating layer between the surrounding holding means is mounded into a series of domed 'solar caps', often in a grid array.

The undulating structure performs a number of advantageous functions:

The support structure raises the sheet material and solar power generating means above the level of the decomposing material and/or the capping support layer. Advantageously, this renders the solar power generating means less prone to damage.

The sloping side walls also reduce the formation of puddles or pools of rainwater, and the accumulation of dirt or debris on the solar power generating layer and / or solar power generating means (usually solar photovoltaic cells). This may otherwise reduce the power generating efficiency of the solar power generating means.

The slopes of the solar caps also channel rainwater and dirt or debris onto the upper surface of the holding means where it may drain from the top of the capping assembly.

A proportion of gases leaking through the base layer and the overburden beneath each solar cap will accumulate and be captured at the highest points of the solar cap (facilitated by the largely unencumbered movement of landfill gases through the boulder or gravel within the solar cap), where they can be dealt with as further described hereinbelow.

Where the installation is in an area significantly far from the equator some of the sloping side walls may usefully be at an angle to the horizontal, and face in the direction, that maximises the amount of sunlight falling on the solar power generating means (for example solar photovoltaic cells).

The solar cap mounds may often be so constructed that all the sloping side walls of the sheet units of the solar power generating layer, or in the case of square or rectangular sheet units, the two members of a pair of opposing side walls are inclined at the same angle to the horizontal. Where the installation is in an area significantly far from the equator it may be preferred to have solar photovoltaic cells only on the side wall face which faces in the direction and which is also inclined at an angle that maximises the amount of sunlight falling on the solar layer; the other side walls may be inclined at any desired angle.

Where the sheet units of the solar power generating layer are rectangular or square, the solar cap mounds may conveniently be pyramidal, or may have a shallower slope towards their midpoints and a steeper slope towards the depressions between them.

The sheet unit covering each solar cap is usually constructed from smaller component sheets. It will be necessary to construct the, for example square or rectangular solar power generating layer sheet unit such that it is able to conform to the surface of for example a pyramidal mound. It will be appreciated that in order to do so folding, cutting and/o suitably overlapping points at the edges and/or corners of the component sheets will be necessary.

As described hereinabove, it will be necessary to have any parts of the edge portions of the sheet units that lie under the holding means be devoid of solar power generating means. It may also be necessary to have other areas of the of the solar power generating layer be devoid of solar power generating means where they would interfere with the necessary shaping of the sheet unit described above. The skilled person will be able to calculate the appropriate points at which, and the degree to which any of the foregoing will be necessary.

The desired angle from the horizontal of the side walls, and the stability of the surface slope of a heap or pile of any particular material at that angle will determine the materials used in the support structure.

The support structure mounds may be produced by earth-moving equipment to position such materials as one of more of gravel, rock, ash, clay, boulders and soil on the surface of the overburden. Alternatively, the mounds may be produced by placing rounded and/or porous structures made or metal, wood, plastic, concrete or any other like material on the surface of the overburden, to provide a zone of largely unencumbered gas permeability so as to allow accumulation of landfill gas at or near to the summit of each solar cap.

Gravel, boulders or rounded and/or porous structures may have a mean size of >1 cm in diameter, for example >20cm in diameter, >50cm in diameter or >100cm in diameter.

Additionally or alternatively, it is also convenient as noted hereinabove that each mound is formed by increasing the thickness of the overburden at suitable points. For example, the overburden may comprise in ascending order a layer of sand or earth on the base layer, a layer of boulders or gravel and then a layer of earth, clay or sand (optionally with rounded or gas permeable structures made or metal, wood, plastic, concrete or any other like material on the surface of the overburden).

It is then convenient to increase the thickness of one of the layers, preferably the layer of boulders or gravel so as to allow largely unimpeded passage of the landfill gases to or near the summit of the solar cap. The boulders or gravel may have a mean size of >1cm in diameter, for example >20cm in diameter, >50cm in diameter or >100cm in diameter. Such largely unimpeded passage of landfill gases is not the normally the case through compacted waste held in landfill or dump sites.

Much less preferably, the mounds may be similarly produced on the surface of the capping support layer prior to laying down the base layer on the capping support layer, so as to introduce mounds and undulations beneath the base layer. In general this will only be feasible where the angles of inclination on the mounds are slight, since holding the edge portions of adjacent sheet units of the base layer together under the overburden on steep slopes will be much less feasible. As noted hereinabove, preferably the surface of the decomposing material is covered with a capping support layer with a relatively even surface for supporting the base layer, to provide an even surface on which the capping assembly is laid down. It is preferred that the capping support layer is built up to form an even terrain of raised ground higher than the perimeter or rim of the landfill at ground level.

Where the surface of the capping assembly comprises a plurality of solar caps, separated around their edges by holding means, it will be seen that the sloping walls of the solar caps and the holding means respectively define the side walls and bottoms of a plurality of elongate depressions in the capping assembly. These are in the form of furrows or channels, running between adjacent solar caps, generally in a grid pattern, so that the surface of the capping assembly is undulating. Each such elongate depression will preferably run to a point on the perimeter of the site, and preferably each runs between two points on the perimeter of the site.

To promote drainage from the surface of the capping assembly, any capping support layer and/or the overburden are preferably so constructed that each elongate depression is aligned down at least one downwardly sloping surface towards the perimeter of the installation. That is, for example a channel may be provided, in which part of the channel is higher than one end at the perimeter of the site, so that the channel is inclined along part of its length, and water will run downhill along the channel to the perimeter of the site.

It may be convenient for the surface of the capping assembly to slope downwards from a central point. If the channels are in a perpendicular grid pattern extending across substantially all of the site, then not all the channels will run directly downhill, but some will run skew downhill, and most channels will slope in two opposite directions from their central point to the perimeter of the site. The maximum slope of the channels will be of the order of 15 to 30 degrees to the horizontal.

Such drainage reduces the pooling of rainwater on top of the site (especially in regions of heavy rainfall, such as equatorial, tropical and temperate western maritime regions). In addition to the fluid impermeability of the solar power generating layer and holding means, it also reduces the penetration of such rainwater into the decomposing waste to contribute to toxic leachate from the site, for example into the surface and groundwater.

In general the angle of inclination of the side walls and of the bottom of the depressions will be determined by a balance of factors, including the maximum rate of rainfall that the drainage from the capping assembly that is required, and the potential loss of output from the cells of the solar layer if they are aligned too far from the angle at which maximum potential solar irradiation is incident on them. The skilled person will be able to calculate the optimum values.

It is preferred that each solar cap is provided with gas collection means to deal with the gases (for example methane, hydrogen and carbon dioxide) that leak throug the base layer.

Preferably, each solar cap is provided with at least one upright porous or perforated metal or plastics pipe running through the solar power generating layer into the overburden to the base layer, but not passing beyond the latter. More preferably, one such 'peak' porous or perforated metal or plastics pipe is provided at or near the highest point of the solar cap.

Optionally, in a rectangular solar cap, an upright 'midpoint' pipe is provided at or near the midpoint of the most direct slope down to each of the surrounding holding means and/or near the midpoint of the slope down to the corners of the solar cap. Preferably the midpoint pipes communicate with the peak porous or perforated metal or plastics pipe, and it is in turn fitted with a take-off pipe through which the gases are taken off to be used, typically for energy production, typically electricity or heat generation.

For reasons of safety, the take-off pipe is preferably fitted with a back-flow preventer, such as a non-return valve. Each peak drill casing is preferably fitted at or near its upper end with a pressure-sensitive gas release and flare-off device. In the event of the device detecting gas overpressure above a preset safe value beneath the solar cap on which it is mounted, it vents gas into the atmosphere and may desirably ignite such gases, usually with an electric spark. In a second preferred embodiment of the second aspect of the present invention, there is provided a method for constructing an installation for generating solar power, comprising

covering a mass of decomposing material with a capping assembly, comprising optionally laying a base layer above the decomposing material, comprising a plurality of flexible sheet units of a fluid impermeable material, such that the edge portions of neighbouring sheet units are adjacent;

laying an overburden above the edge portions to form a partially fluid- impermeable base layer;

laying a solar power generating layer above the base layer, where said sheet material has solar power generating means bonded thereto, or the method comprises the further step of bonding said solar power generating means to the sheet material, such that the edge portions of neighbouring sheet units are adjacent and

laying holding means above the edge portions of the solar power generating layer such that they are held together by the weight of the holding means to form a substantially fluid-impermeable solar power generating layer.

Preferably, the method further comprises the step of providing a support layer over the decomposing material, for supporting the capping assembly.

Preferably, the method further comprises the step of installing a protective layer above the overburden to protect the underside of the solar power generating layer.

The installation is preferably constructed so that at least a portion of the solar power generating layer is undulating, and comprises a series of mounds, each · bearing the solar power generating layer as a solar cap, and separated by elongate depressions, the bottoms of which are defined by elongate holding means.

Accordingly, the method of the second preferred embodiment may further comprise the steps of preparing a plurality of mounds on or as part of the overburden, each mound being separated from each adjacent mound by a depression,

covering each mound with a sheet unit of the solar power generating layer; the edge portions of each sheet unit lying at the bottom of a depression adjacent to the edge portions of a neighbouring sheet unit, and then

applying holding means to the edge portions, so that they are held together by the weight of the holding means above the edge portions to form a substantially fluid-impermeable solar power generating layer. As noted above, in the installation for generating solar power of one form of the second preferred embodiment of the first aspect of the invention, and the holding means comprises an upper part and a lower part. The upper and lower parts sandwich the edge portions of the sheet units of the solar power generating layer, and the lower part of the holding means extends beyond the edge portions under a part or all of the solar power generating layer. The base layer may be omitted, in which case, the overburden lies directly on the mass of decomposing material or a capping layer.

Accordingly in one form of the second preferred embodiment of the second aspect of the present invention, there is provided a method for constructing an installation for generating solar power, comprising the step of covering a mass of decomposing material with a capping assembly, comprising

optionally laying a base layer above the decomposing material or a capping layer;

laying an overburden above the decomposing material to form a partially fluid- impermeable base layer,

applying the lower part of the holding means to at least some of the overburden, such that it will extend under a part or all of the solar power generating layer in use;

covering the holding means with the edge portions of sheet units of the solar power generating layer, such that the edge portions of each sheet unit lies adjacent to the edge portions of a neighbouring sheet unit, and then

applying the upper part of the holding means if present to the edge portions, so that they are held together by the weight of the holding means above the edge portions to form a substantially fluid-impermeable solar power generating layer. Preferably, the lower part of the holding means is fluid impermeable. Preferably, the lower part of the holding means comprises a rubber asphalt.

The installation is preferably constructed so that at least a portion of the solar power generating layer is undulating, and comprises a series of mounds, each bearing the solar power generating layer as a solar cap, and separated by elongate depressions, the bottoms of which are defined by elongate holding means. Accordingly, the method may further comprise the steps of

preparing a plurality of mounds on or as part of the overburden, each mound being separated from each adjacent mound by a depression,

applying the lower part of the holding means to at least some of the depressions and covering at least some of the mounds with sheet units of the solar power generating layer, the edge portions of each sheet unit lying at the bottom of a depression on the lower part of the holding means and adjacent to the edge portions of a neighbouring sheet unit, and then

applying the upper part of the holding means if present to the edge portions, so that they are held together by the weight of the holding means above the edge portions to form a substantially fluid-impermeable solar power generating layer.

Preferably the surface of the decomposing material is first covered with a capping support layer with a relatively even surface to provide an even surface on which the capping assembly is laid down. It is preferred that the capping support layer is built up to form an even terrain of raised ground higher than the perimeter or rim of the landfill at ground level. The present capping assembly may be retrofitted to an existing site, in particular a landfill or dump site. Existing sites will often be made up of decomposing material heaped into a plateau higher than the perimeter of the site, with an uneven surface. Depending on how uneven the surface is, it may be preferred to partially level the surface before applying and evening out a capping support layer.

The mounds may each be constructed to be a hillock or hummock or they may be constructed to be elongate ridges, in each case with elongate depressions between them, the side walls of which are formed by the sheet units of the solar power generating layer. The depth of the depressions will depend on the angle to the horizontal of the side walls, and at lower angles, they will be relatively shallow.

In a preferred form of this embodiment of the invention, each mound is constructed to comprise a continuous or discontinuous layer of boulders and/or gravel, which .may have a mean size of >1cm in diameter, for example >20cm in diameter, >50cm in diameter or >100cm in diameter. The boulders or gravel afford improved gas permeability. The interstitial spaces between the boulders or gravel allow for relatively unimpeded gas permeation through the capping assembly. This situation differs significantly from the remainder of the compressed mass of waste material which is far from uniform or easily permeable to landfill gases.

In this manner, landfill gases that have escaped capture by conventional vertical porous or perforated riser shaft gas collection pipes or drill casings installed within the decomposing material can make their way more easily to the underside of the solar power generating layer in each solar cap. Such landfill gases will accumulate at or near to the summit of each solar cap, and can be reliably extracted at specific points from the solar caps in the installation, and dealt with as further described hereinbelow. Preferably, at least a portion of each mound surface is constructed to have a slope of at least 5 degrees to the horizontal, more preferably, at least 15 degrees to the horizontal, in particular at least 25 degrees to the horizontal. These angles may be measured in any direction on the surface of the capping assembly, but preferably in the direction of greatest slope. Where the installation is in an area significantly far from the equator some of the sloping side walls may usefully be at an angle to the horizontal, and face in the direction, that maximises the amount of sunlight falling on the solar power generating means.

Preferably, the support structure is constructed to comprise a series of mounds, separated by elongate depressions, such as furrows or channels. Such mounds may generally be constructed in a rectangular grid pattern, so that at least a portion of the solar power generating layer is undulating. The mounds are produced on the surface of the capping support layer prior to laying down the solar generation layer, so as to introduce mounds and undulations beneath the layer. The solar generation layer rises and falls over the mounds and depressions, forming a 'solar cap' over each mound, the sloping walls of the solar caps defining the side walls of the elongate depressions in the capping assembly.

The method for constructing an installation for generating solar power, comprising constructing a capping assembly over a mass of decomposing material may thus comprise the steps of constructing a support structure in the form of an undulating surface above the decomposing material, and covering it with a substantially gas-impermeable flexible sheet material, wherein said sheet material has solar power generating means bonded thereto.

An advantage of this installation is that the consequent undulating surface of the solar power generating layer raises the sheet material and solar power generating means above the level of the decomposing material and/or the capping support layer. Advantageously, this renders the solar power generating means less prone to damage. Another advantage of this installation is that the consequent undulating surface enhances the ability of the structure to reduce the formation of puddles or pools of rainwater, and the accumulation of dirt or debris on the solar power generating layer and / or solar power generating means (usually solar photovoltaic cells) which may otherwise reduce the power generating efficiency of the solar power generating means, and its ability to channel rainwater and dirt or debris onto the upper surface of the holding means where it may drain from the top of the capping assembly. The bottom of the depressions may be constructed to be relatively flat and/or broad, so that they may be advantageously used to provide access thoroughfares, such as pathways or walkways between the solar caps, for example for inspection and maintenance. Where the surface of the capping assembly comprises a plurality of solar caps, it will be seen that the sloping walls of the solar caps and bottoms form a plurality of elongate depressions in the capping assembly, such as furrows or channels, running between adjacent solar caps, generally in a grid pattern. Preferably the assembly is so constructed that each such elongate depression will run to a point on the perimeter of the site, and more preferably each runs between two points on the perimeter of the site.

To promote drainage from the surface of the capping assembly, any capping support layer is preferably so constructed that each elongate depression is aligned down at least one downwardly sloping surface towards the perimeter of the installation, or upwardly and then downwardly between two points on the perimeter of the site.

The site is preferably constructed with the decomposing material and/or a capping support layer built up to form an even terrain of raised ground higher than the perimeter or rim of the site at ground level to enhance the complete drainage of rainwater and/or removal of dirt and debris from the capping assembly, and it may be necessary to make the sides of the raised terrain fall away steeply, for example at about 45 degrees to the horizontal. The surface of the support structure may then be covered by a protective layer comprising a number of sheet units, which are typically laid over the support structure and bonded together at the edges in situ, for example by heat sealing, hot wedge or hot air welding, chemical fusion or adhesion, or fixed firmly together at the edges, preferably to form a significantly fluid-proof seal, for example by fastening means, such as, preferably elongate, closures along a seam, for example, elongate clips, clasps or slides, or a plurality of staples. Alternatively, a number of smaller sheets may be laid over the support structure and bonded together at the edges in situ to form a number of sheet units which are then in turn bonded together in situ, for example by the above methods.

Where the capping support layer forms a terrain raised above the perimeter of the installation, its sides are also covered with sheet units of the protective layer bonded together at the edges and bonded to the edge portions of the sheet units of the layer on the top, all for example by the above methods.

The surface of the support structure or the protective layer may then be covered by the solar power generating layer, or a precursor thereof without solar power generating means, comprising a number of sheet units, which are may then be bonded together at the edges in situ, for example by heat sealing, hot wedge or hot air welding, chemical fusion or adhesion, or fixed firmly together at the edges to form a fluid-proof seal, for example by fastening means, such as, preferably elongate, closures along a seam, for example, elongate clips, clasps or slides. Where the sheet units are precursor sheets, solar power generating means are then attached to the precursor sheet units, as described in greater detail in relation to the Figures.

More usually, a number of smaller sheets are bonded together in situ, for example by the above methods, to form sheet units of the solar power generating layer, or a precursor thereof without solar power generating means, for installation. Again, where the sheet units are precursor sheets, solar power generating means are then attached to the precursor sheet units, as described in greater detail in relation to the Figures. Individual component sheets, for example of 2m x 5.8m, may bear attached solar photovoltaic cells, for example four such cells, with the photovoltaic cells electrically connected together, which are then bonded together at the edges in situ to form a number of sheet units which are then in turn bonded together in situ, all for example by the above methods.

Alternatively, precursor sheet units or component sheets may be similarly installed, and a solar power generating layer made up from a precursor layer, sheet unit or sheet by attaching solar power generating means to it in situ.

Where the means comprise or consist of a number of flexible thin-film solar photovoltaic cells, for example comprising amorphous silicon or polycrystalline materials such as nano-crystalline silicon, protocrystalline silicon, cadmium telluride (CdTe), and copper indium gallium selenide (CIS, CIGS) or printed semiconductor thin-film photovoltaic cells, the solar power generating means may be adhered to the relevant substrate under pressure using a specialized heat- melt adhesive, as described hereinbelow in relation to the Figures.

Where the capping support layer forms a terrain raised above the perimeter of the installation, its sides are also covered with sheet units of the solar power generating layer. These are bonded together at the edges and bonded to the edge portions of the sheet units of the layer on the top, all for example by heat sealing, hot wedge or hot air welding, chemical fusion or adhesion, or fixed firmly together at the edges to form a fluid-proof seal, for example by fastening means, such as, preferably elongate, closures along a seam, for example, elongate clips, clasps or slides.

The first preferred embodiment of the first aspect of the present invention may be provided with a base layer above the decomposing material, comprising a plurality of flexible sheet units of a fluid impermeable material.

Accordingly, in another form of the first preferred embodiment of the first aspect of the present invention, there is provided an installation for generating solar power, comprising:

a mass of decomposing material; and; a capping assembly, comprising

a base layer above the decomposing material, comprising a plurality of flexible sheet units of a fluid impermeable material, and

the solar power generating layer being installed on a support structure which comprises at least two man-made mounds.

The edge portions of neighbouring sheet units in the base layer being adjacent and held together only by the support structure above the respective edge portions, which are then preferably overlapped. More preferably, however, the sheet units of the base layer will be bonded together at the edges, for example by heat sealing, hot wedge or hot air welding, chemical fusion or adhesion, or fixed firmly together at the edges, preferably to form a significantly fluid-proof seal, for example by fastening means, such as, preferably elongate, closures along a seam, for example, elongate clips, clasps or slides, or a plurality of staples. The sheet units of the base layer · may lie on the upper surface of the decomposing material, or preferably on the upper surface of a capping support layer, which may reduce damage to the base layer by providing a smoother surface for supporting the base layer. Suitable and preferred dimensions, materials and structures for the base layer, the capping support layer, the support structure, the solar power generating layer, the solar power generating means, are as so described hereinbefore for these integers in general for the first and second preferred embodiments of the first aspect of the present invention

In another form of the first preferred embodiment of the second aspect of the present invention, there is provided a method of constructing the installation immediately above for generating solar power, comprising

covering a mass of decomposing material with a capping assembly, comprising laying a base layer above the decomposing material, comprising a plurality of flexible sheet units of a fluid impermeable material; constructing a support structure which comprises at least two man-made mounds on the base layer; and

The support structure may (less usually) be constructed on the surface of the decomposing material. In general, however, the decomposing material is covered over with a capping support layer, and the base layer is laid on the capping support layer.

Suitable and preferred dimensions, materials and structures for the base layer, the capping support layer, the support structure, the solar power generating layer, the solar power generating means, and methods for incorporating these integers into the installation, are as so described hereinbefore for these integers in general for the first and second preferred embodiments of the second aspect of the present invention.

Detailed Description of the Invention

Preferred embodiments of the present invention will now be described, by way of example only, and not in any limitative sense, with reference to the accompanying drawings in which:

Figure 1 illustrates a schematic cross-section of part of an existing landfill site installation to which a capping assembly according to the first preferred embodiment of the first aspect of the present invention has been retrofitted;

Figure 2 illustrates a part of a capping assembly used to cap a landfill site according to a first embodiment of the first aspect of the present invention;

Figure 3 illustrates a portion of a solar power generating layer used to cap the landfill site of Figure 1 ; Figure 4 illustrates a cross-section of key parts of the upper part of a capped landfill site installation according to the second preferred embodiment of the first aspect of the present invention, including key parts of the capping assembly: Figure 5 illustrates a schematic cross-section of part of an existing landfill site installation to which a capping assembly according to the present invention has been retrofitted;

Figure 6 illustrates a schematic cross-section of part of a landfill site installation according to a first embodiment of the present invention;

Figure 7 illustrates a schematic cross-section of a half portion of a solar cap bearing an impermeable solar power generating layer used to cap the landfill site of Figures 4 and 5;

Figure 8 illustrates a plan view of the solar cap of Fig 7.

Figure 9 illustrates a schematic perspective view of the top of a landfill site installation according to the second preferred embodiment of the first aspect of the present invention.

Figure 1a shows a cross-section of the upper part of an unsealed landfill site 100 comprising decomposing material 102 which forms an irregular plateau 152 falling away relatively steeply at its perimeter 154.

Figure 1b shows a cross-section of the upper part of the same landfill site 100, where the plateau 152 has been given an even surface 155 by moving some of the decomposing material 102, and placing a capping support layer 126 of earth on it with an even surface that slopes slightly away from the viewer with an incline of between 5° and 25°).

Above the capping support layer 126, is a capping assembly 104, in which fluid- impermeable sheet units 112, here in the form of a weather and abrasion resistant PVC sheets 106, of a type used in the capping of landfill, typically around 0.75 millimetres thick. The sheets 106 are bonded together, for example by heat sealing, hot wedge or hot air welding, chemical fusion or adhesion, or fixed firmly together at the edges to form a significantly fluid-proof seal, for example by fastening means, such as, preferably elongate, closures along a seam, for example, elongate clips, clasps or slides, in order to produce a solar power generating layer 110.

These sheets 106 have solar power generating means134, in the form of amorphous silicon thin-film solar photovoltaic cells (shown in Figure 3), bonded to an upper surface thereof, for producing electric power from sunlight incident thereupon.

The solar power generating layer 110 is supported on a support structure 1 17 comprising a plurality of pyramidal mounds 119, and is formed into a series of shallow solar caps 150. Each cap 150 is supported on a pyramidal mound 1 19 and sealed together to form a fluid-tight seal around their perimeters 151 , for example by the above methods, to form a series of shallow furrows 136 separating the solar caps 150.

The furrows 136 and form drainage means in part down the slope on the support layer 126 surface, so that any surface water, dirt or debris will be swept downhill under the influence of gravity, wind and rain, and access means, for example for solar power layer maintenance.

The mounds 1 19 are produced by using earth-moving equipment to position material such as a mineral particulate, here gravel.

At the perimeter 154, the sloping sides 156 of the plateau 152 are covered with sheet units 157 of the sheet material of the solar power generating layer without solar power generating means, which are conventionally bonded together, for example by heat sealing, hot wedge or hot air welding, chemical fusion or adhesion, or fixed firmly together at the edges to form a significantly fluid-proof seal, for example by fastening means, such as, preferably elongate, closures along a seam, for example, elongate clips, clasps or slides. The upper edge portions 158 of the sheet units 157 pass under the edge portions 160 of the solar power generating layer 110 at the perimeter 154 and are conventionally bonded to it to form a fluid-tight seal 162, for example by the above methods.

Gas vent pipes (not shown in Figure 1 b) can be included to enable controlled release of landfill gases produced by the breakdown of the waste material 102 in a controlled manner and these gases can be directed to a burner, or through a methane and/or hydrogen recovery unit to a gas turbine generator (not shown) in order to produce heat or electricity respectively.

Referring to Figure 2, a landfill 100 contains waste material 102 and is covered with a clay capping support layer 26, which assists in the sealing of the waste material 102 into landfill 100 and provides support for a support structure 117 unit, here a mound 119, part of which 115 is formed from a mineral particulate, which is typically gravel. Below the impermeable solar power generating layer 110 an upper clay layer 113 forms part of the mound 119, assists in the sealing of gases from the waste material 102 into landfill 100, and protects the PVC sheet 106 of a solar power generating layer 110.

A solar power generating layer 1 10 provides a barrier to substantially prevent gas produced by the decomposition of the waste material 102 from escaping from the landfill 100 to the atmosphere above, and forms a solar cap 150 over the mound 119. The solar power generating layer 110 is formed from a flexible sheet material, in the form of a weather and abrasion resistant PVC sheet 106, of a type used in the capping of landfill and is typically around 0.75 millimetres thick, having solar power generating means134, in the form of amorphous silicon thin- film solar photovoltaic cells (shown in Figure 3), bonded to an upper surface thereof, for producing electric power from sunlight incident thereupon, and is installed on the surface of the mound 119.

Gas vent pipes are included to enable controlled release of landfill gases produced by the breakdown of the waste material 102 in a controlled manner. These gases can be directed to a burner or through a methane and/or hydrogen recovery unit to a gas turbine generator (not shown) in order to produce heat or electricity respectively. Amongst these pipes, plastics or metal porous or perforated vertical riser shaft gas collection pipes or drill casings 200, which penetrate the decomposing material 102, are included to enable controlled release of landfill gases produced by the breakdown of the waste material 102, and these each communicate at its upper end with a methane, hydrogen recovery unit or gas well head 256 (not shown) and thence with one or more collection mains 202 (not shown) by which the gases can be directed to a burner or through a methane and/or hydrogen recovery unit to gas turbine power generating means (not shown) in order to produce heat or electricity respectively. These landfill gases are extracted under negative pressure.

The solar cap 150 also has secondary porous or perforated gas collection pipes 203 and 205, laid out on the respectively in two sets of four at the corners of two concentric squares to enable the collection of landfill gases produced by the breakdown of the waste material 102 which into the mound 119 under the solar power generating layer 110. Each respectively rests on a base flange 252, 262 (not shown) on the capping support layer 126 and extends through the mound 119 and the solar power generating layer 110. The sheet unit 112 of the solar power generating layer 110 rests on, and is sealed with adhesive to, respectively upper support flanges 254, 262 (not shown) each mounted near the upper end of the pipes 203, 205.

All these pipes 203, 205 may communicate with each other and/or with the pipes 200 though collection mains 202 (not shown) and from there to a burner in a steam generator, or though a methane and/or hydrogen recovery unit to a gas turbine engine, and the steam generator or engine powers an electrical generator.

The solar power generating layer may be formed by bonding the thin-film power generating means (for example, thin-film amorphous silicon solar laminates available from United Solar Ovonic) onto a sheet using an adhesive. The sheet may be, for example a single-ply PVC membrane (such as one available from Sika Sarnafil), and the adhesive may be, for example a heat-melt adhesive. A typical bonding process includes the following steps:

Step 1 -Plasma treatment: A sweeping flame treatment is used to clean the back surface of the photovoltaic laminates to remove impurities and to increase the surface tension to allow for a more effective adhesion process;

Step 2-Lamination: The solar laminates are adhered to a roll of the PVC sheet under pressure using a specialized heat-melt adhesive to form the solar power generating layer. Step 3-Curing: The solar power generating layer is cured for a certain curing period.

Step 4-Edge sealing: An edge sealant is applied to the edges of the laminates to provide further protection from moisture and sunlight.

Step 5-Wiring: A wiring harness is attached to the solar power generating layer, together with a cast plastics (for example polyamide) housing over wiring solder points, and an additional membrane patch over a series interconnection area.

With reference to Figure 3, the solar power generating layer 110 is formed from sheets 106, which may be rolled for convenient handling. Each sheet 106 is formed from a flexible sheet material, in the form of a weather and abrasion resistant PVC sheet 108, of a type used in the capping of landfill and is typically around 0.75 millimetres thick, having solar power generating means134, in the form of amorphous silicon thin-film solar photovoltaic cells, arranged on and bonded to an upper surface thereof, leaving edge portions 120 uncovered, for producing electric power from sunlight incident thereupon. A wiring harness 135 attaches to the solar power generating means 134 together, and is attached to the layer sheets 108. A cast plastics (for example polyamide) housing over wiring solder points, and an additional membrane patch over a series interconnection area, are provided but not shown. . When to be installed on a landfill, the sheets 108 are rolled out to cover the surface of a mound 119. Edge portions 120 of neighbouring sheets 108 can be overlapped and bonded together, for example by heat sealing, hot wedge or hot air welding, chemical fusion or adhesion, or fixed firmly together at the edges to form a fluid-proof seal, for example by fastening means, such as, preferably elongate, closures along a seam, for example, elongate clips, clasps or slides.

Referring to Figure 4, an installation for generating solar power according to the first aspect of the present invention comprises a landfill 100 comprising a mass of decomposing material 102,

and a capping assembly 104, comprising

a base layer 106 above the decomposing material 102, comprising a plurality of flexible sheet units 108 of a fluid impermeable material, and

a solar power generating layer 1 10 above the base layer, comprising a plurality of sheet units 112 of a flexible fluid impermeable material with solar power generating means 134 bonded thereto for producing electric power from sunlight incident on at least a portion of the installation,

wherein

in the base layer 106, the edge portions 116 of neighbouring sheet units 108 are adjacent, here overlapping, and held together by the weight of an overburden 118 above the edge portions 116a, 116b, 116c, to form a partially fluid- impermeable base layer 06, and

in the solar power generating layer 110, the edge portions 120 of neighbouring sheet units 112 are adjacent, here overlapping, and held together by the weight of a holding means 121 , having an upper part 122 above and lower part 124 below the edge portions 120 to form a substantially fluid-impermeable solar power generating layer 110.

As depicted, the edge portions 116b of the base layer 106 are coincidentally directly below the edge portions 120 in the solar power generating layer 110. Thus, the edge portions 116b are held together not only by the weight of the overburden 118 but also by the weight of the holding means 121.

In more detail, a capping support layer 126, here of earth, overlying the waste material 102 provides an even surface to support the base layer 106 and the rest of the capping assembly 104. The capping support layer 126 slopes slightly downwards away from the viewer to the edge of the landfill 128 (not shown).

The base layer 106 is formed from flexible sheet material, in the form of a plurality of geomembrane sheet units 108. In the base layer 106, the edge portions 116a, 1 16b, 116c of neighbouring geomembrane sheet units 108 overlap.

The overburden 118 comprises layers of sand or earth 127, and earth 128, and lies over all the sheet units 108 of the base layer 106 in the capping assembly 104. These overlapping geomembrane sheet units are not glued or fused together by any means.

A support layer 132, here of elastomeric shred composite is let into the upper surface of the top earth layer 128 of the overburden 118. The lower part 124 of the holding means 121 , here asphalt rubber, lies on and is coterminous with the support layer 132. A protective layerl 14, here a light weight sheet of low-density polyethylene, lies over the top surface of the top earth layer 128 of the overburden 118 and the top surface of the lower part 124 of the holding means 121. This protective layer 114 serves to protect the solar power generating layer 110 from any deleterious effects of the overburden 18 on the joints and sealing of component sheets of sheet units 1 12 of the solar power generating layer 110, here of PVC, which lies over the protective layer 114, The edge portions 120 of neighbouring sheet units 112 of the solar power generating layer 110 overlap extensively on top of the lower part 124 of the holding means sandwich 121. The upper part 122 of the holding means 121 , here of asphalt rubber, overlies the edge portions 120 and adheres to them to form a fluid impervious seal, and is of a similar width to the lower part 124, here also of asphalt rubber, of the holding means 121. Where the sheet units 1 12 of the solar power generating layer 1 10 pass under the upper part of the holding means 121 , they are devoid of solar power generating means 134. On each side of the holding means 121 the overburden 118 is built up into an upward slope 125 of about 5 degrees from the horizontal by a central layer 130 of boulders. The boulder layer allows unimpeded passage of landfill gases to the summit or near the summit of the solar cap assembly 104 via the interstitial spaces between boulders.

The edge portions 116 of the base layer unit sheets 106 are held together by the weight of the overburden 1 18 with as appropriate the weight of the holding means 121. The base layer 104 provides a barrier to partially prevent gas produced by the decomposition of the waste material 102 from escaping from the landfill 100.

The fluid-impermeable PVC solar power generating sheet unit 110 has a solar power generating means 134, here in the form of flexible thin-film photovoltaic power generating means, bonded to the upper surface thereof. The flexible thin- film solar power generating means 134 here comprises amorphous silicon thin- film solar photovoltaic cells, but may also comprise any other flexible thin-film material capable of generating power from solar irradiation, examples of which are listed hereinbefore. . The sheet units 112 of the solar power generating layer 110 is of a type used in Building Integrated Photovoltaic roofing and is typically around 0.5 to 2.0 millimetres thick. The solar power generating layer 1 10 remains exposed to the atmosphere, so that the solar power generating means 134 receives sunlight. It is therefore important that both the sheet units 112 and the solar photovoltaic cells 134 of the solar power generating layer 1 10 are weather resistant (i.e. resistant to wind, rain, sun, UV light, and extremes of temperature) and resistant to abrasion by dust and particles. It will be appreciated that all the elements of such key parts of the capping assembly recited above, extend towards and away from the viewer along or parallel to the overlaps of the sheet unit end portions 116 and 120, and may extend in each direction as far as the perimeter of the landfill 102.

The upper part 122 of the holding means 121 thus forms the base of a shallow depression or furrow 36, of which the slopes 25 form the side walls. As the capping support layer 126 slopes slightly downwards away from the viewer to the perimeter of the landfill 128 (not shown), the base of the depression or furrow also slopes in the same direction. This means that the depression or furrow 136 formed as part of the solar cap assembly 104 atop of capping support layer 126 acts as a drainage channel for the surface of the capping assembly. Depending on the transverse dimension of the base, it may also act as a walkway or roadway.

The structure shown in Figure 4 replicates to the left and right as shown schematically in Figure 5, so that the slopes 125 are each a slope on one side of a pyramidal solar cap 150.

The flexible thin-film power generating means 134 (for example thin-film amorphous silicon solar laminates available from United Solar Ovonic) are bonded to the sheet units 112 of the impermeable solar power generating layer 1 10 using a heat-melt adhesive. As an alternative to PVC the sheet units 1 12 may be of a flexible polyolefin FPO membrane with a polyester scrim and glass fibre carrier available from Sika Samafil)

A typical process of producing a sheet unit 1 12 of the solar power generating layer 110 which bears thin film power generating means 134 includes the following steps:

Step 1 -Plasma treatment: A sweeping flame treatment is used to clean the back surface of the photovoltaic laminates 134 to remove impurities and to increase the surface tension to allow for a more effective adhesion process; Step 2-Lamination: The solar laminates 134 are adhered to a roll of a sheet material suitable as a component sheet of the intended sheet unit 112 of the solar power generating layer 110, under pressure using a specialized heat-melt adhesive.

Step 3-Curing: The impermeable sheet bearing the solar laminates 134 is cured for a certain curing period.

Step 5-Wiring: A wiring harness is attached to the impermeable sheet, together with a cast polyamide housing over wiring solder points, and an additional membrane patch over a series of interconnection areas

Step 6- Formation of Sheet Unit 112: The edges of the of the sheets (each usually 2m x 5.8m is size or larger) are joined to together using heat so as to form a much larger (for example 50m x 50m) sheet unit 112. bearing the solar laminates 134. The sheets may be so mutually positioned in the joining process to form for example a pyramidal or domed sheet unit as the basis of a solar cap.150, as shown in Figures. 5b and 6.

The formation of the installation 100 of Figure 4 is carried out conventionally by laying down and as appropriate sealing the components described above in order from the bottom upwards.

The method of sealing the edges of the capping assembly to render the capping assembly fluid-impermeable to the atmosphere has been described hereinbefore.

In Figure 5, details that are described with reference to Figure 4 have been omitted for clarity.

Figure 5a shows a cross-section of the upper part of an unsealed landfill site 100 comprising decomposing material 102 which forms an irregular plateau 152 falling away relatively steeply at its perimeter 154. Figure 5b shows a cross-section of the upper part of the same landfill site 100, where the plateau 152 has been given an even surface 155 by moving some of the decomposing material 102, and placing a capping support layer 126 of earth on it with an even surface that slopes slightly away from the viewer.

The capping support layer 126 surface is covered with a partially fluid- impermeable base layer 106, formed as described with reference to Figure 4. Above the base layer 106, a solar power generating layer 1 10 is formed into a series of shallow pyramidal solar caps 150, supported on an overburden 118 and held down and sealed around their perimeters 151 by holding means 121 (not shown) to form a series of shallow furrows 136 separating the solar caps 150 and forming drainage means in part down the slope on the support layer 126 surface.

At the perimeter 154, the sloping sides 156 of the plateau 152 are covered with sheet units 157 of base layer material which are conventionally bonded together to from a fluid solar power generating layer. The upper edge portions 158 of the sheet units 57 pass under the edge portions 160 of the base layer 106, and are conventionally bonded in the area of overlap to form a fluid-tight seal 162 The solar power generating layer 110 at the perimeter 154 extends down over all the sheet units 157 on the sides 156, and is conventionally bonded to them to form a fluid-tight seal.

Referring to Figure 6, the landfill 100 may also include an impermeable base layer formed from a layer of clay and a geomembrane beneath the waste material in the case of an engineered landfill site (none shown). Plastics or metal porous or perforated vertical riser shaft gas collection pipes or drill casings 200, which penetrate the decomposing material 102, are included to enable controlled release of landfill gases produced by the breakdown of the waste material 102, and these each communicate with one or more collection mains 202 (not shown) by which the gases can be directed to a burner or through a methane and/or hydrogen recovery unit to gas turbine power generating means (not shown) in order to produce heat or electricity respectively. The flow of the landfill gases within the landfill is shown by the broad arrows 204. These landfill gases are traditionally extracted under negative pressure.

Below the base layer 106 a capping support layer 126 assists in producing an even but sloping surface for the capping assembly 104 and also in providing protection for the PVC base layer 106.

On top of the base layer 106 is a series of pyramidal solar caps 150, formed as described with reference to Figures 1 and 2, and separated by a grid of resulting shallow depressions or furrows 136, with the holding means sandwich 121 at each of their bases.

As shown schematically each solar cap 150 has a central secondary porous or perforated gas collection pipe 206 to enable the collection of landfill gases produced by the breakdown of the waste material 102 which pass through the partially impermeable base layer 106.

Each solar cap 150 also has four mid-point porous drill casings 208 (including one in front of and one behind the central drill casing 206) and these communicate with the central drill casing 206 and from there to a burner or through a methane and/or hydrogen recovery unit to gas turbine power generating means (not shown) in order to produce heat or electricity respectively.

Figure 7 illustrates a schematic cross-section of a half portion of a solar cap 150 bearing an impermeable solar power generating layer 1 10 used to cap the landfill site of Figures 4 to 6. Figure 8 illustrates a plan view of the solar cap of Fig 4. In Figure 7, and details that are described with reference to Figure 4 have been omitted for clarity.

In Figure 7 and 8, the shallow square pyramidal solar cap is contiguous with four identical solar caps 150 (not shown). The solar cap 150 comprises a partially fluid-impermeable base layer 106 bearing an overburden 1 18 which is built up into a slope 125 of 5 degrees in the example shown based on a 50m x 50m pyramidal solar cap 150. The overburden 118 is covered by a solar power generating layer 110 (solar power generating means 134 omitted for clarity to show the sheet unit 112 of the layer 110). The sheet unit 112 is held down and sealed at its edges 120 to an adjacent sheet unit 12 (not shown) of the solar power generating layer 110 in each adjacent solar cap 150 by the holding means sandwich 121 as described with reference to Figure 7. The apex of the pyramid of the solar cap 150 is provided with a secondary upright porous or perforated metal or plastics landfill gas collection pipe ('apical pipe') 250 resting on a base flange 252 on the base layer 106 and extending through to just above the solar power generating layer 1 10. The sheet unit 112 of the solar power generating layer 110 rests on, and is sealed with adhesive to. a pyramidal upper support flange 254 mounted near the upper end of the apical pipe 250. Each face of the support flange 254 slopes downwards towards its bottom edge at 5 degrees. The apical pipe 250 communicates at its upper end with a methane and/or hydrogen recovery unit or gas well head 256. Midway between the apex of the solar cap at the upper end of the apical pipe 250 and each of its edges 258 on lines at right angles to each edge 258, the solar cap 150 is provided with an upright porous or perforated metal or plastics landfill gas collection pipe ('mid-point pipe') 260 (four in total), each resting on a base flange 262 on the base layer 106 and extending through to just above the solar power generating layer 110, i.e. to just above the solar power generating means 34 at that point.

The sheet unit 112 of the solar power generating layer 110 rests on, and is sealed with adhesive to, a flat upper support flange 264 mounted near the upper end of the midpoint drill casing 260.

The upper face of the support flange 264 is mounted skew on the midpoint pipe 260 such that its upper face slopes downwards at 5 degrees to conform to the sheet unit 112 of the solar power generating layer 10. Midway between the apex of the solar cap at the upper end of the apical pipe 250 and each of its corners 268 on, the cap 250 is provided with an upright porous or perforated metal or plastics landfill gas collection pipe ('corner mid-point pipe') 270 (four in total), each resting on a base flange 272 on the base layer 106 and extending through to just above the solar power generating layer 110.

The sheet unit 112 of the solar power generating layer 110 rests on, and is sealed with adhesive to, an upper support flange 264 mounted near the upper end of the corner midpoint pipe 270. The upper face of the support flange 274 is mounted on the corner midpoint pipe 270 and shaped such that its upper face conforms to the sheet unit 122 of the solar power generating layer 110 sealed to it.

Each midpoint pipe 260 communicates at its upper end with the upper end of the apical pipe 250, and with the upper ends of the two adjacent corner midpoint pipes 270, thorough pipes respectively 276 and 278, which run parallel to the solar power generating layer 110.

In Figure 8, the consequential directions of gas flow are shown by the broad arrows. In this way, the gas from all the pipes is collected and fed to the methane, hydrogen recovery unit or gas well head 256.

The take-off pipe to the methane, hydrogen recovery unit or gas well head 256 is preferably fitted with a back-flow preventer, such as a non-return valve. The apical pipe 250 is preferably fitted at or near its upper end with a pressure- sensitive gas release and flare-off device. In the event of the device detecting gas overpressure above a preset safe value beneath the solar cap on which it is mounted, it vents gas into the atmosphere and ignites it, usually with an electric spark.

In the example shown, the solar cap 250 in Figures 4 and 5 is 50 m square at its base, and has an apical height of 2.2 m. Figure 9 illustrates a schematic perspective view of the top of a landfill site installation according to the first aspect of the present invention in which the capping assembly 104 comprises an array of solar caps 150 in a square array are separated by the depressions 136 formed by the sloping walls of the solar caps 150 and the holding means sandwiches 121 lying between them, as described with reference to Figure 7.

The original uneven plateau region 152 of the landfill or dump site as shown in Figure 8a has been provided with a capping support layer 126 (not shown) which underlies the capping assembly 104 shown here. The layer 126 has been provided with an even surface which slopes downwards from a central point in all directions towards the site perimeter, as indicated by the arrows in Figure 9, so that the channels 136 serve as drainage channels for rainwater or stormwater.

It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only, and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims.

Claims

1. An installation for generating solar power, the installation comprising:

a mass of decomposing material; and

a solar power generating layer providing a barrier to gas escaping from and/or entering the mass of decomposing material to/from the atmosphere above, the solar power generating layer comprising a fluid-impermeable flexible sheet material and solar power generating means bonded thereto for producing electric power from sunlight incident on at least a portion of the installation.

2. An installation according to claim 1 , wherein the solar power generating layer comprises a continuous sheet. 3. An installation according to claim 2, wherein the solar power generating layer comprise a number of sheet units bonded together to form a continuous layer.

4. An installation according to any one of the preceding claims, wherein the installation comprises a capping assembly above the decomposing material, comprising the solar power generating layer installed on a support structure which comprises at least two man-made mounds.

5. An installation according to claim 4, wherein the support structure is on the surface of a capping support layer on the surface of the decomposing material.

6. An installation according to claim 4, wherein the solar power generating means comprises thin-film photovoltaic cells. 7. An installation according to claim 6, wherein the thin-film solar photovoltaic cells are amorphous silicon or polycrystalline materials: cadmium telluride and copper indium gallium diselenide; or printed semiconductor thin-film photovoltaic cells 8. An installation according to claim 4, wherein the solar power generating layer comprises a geomembrane.

9. An installation according to claim 4, wherein the solar power generating layer comprises one or more of ethylene propylene diene terpolymer (EPDM); high density polyethylene (HDPE); flexible polypropylene (fPP), reinforced fPP-R; polyvinyl chloride (PVC): thermoplastics polyolefin, includng linear low-density polyethylene (LLDPE) and medium-density polyethylene (MDPE); polyurea, polyamide and polytetrafluoroethylene (PTFE); glass and bitumen- impregnated non-woven geotextile, or polyester reinforced thermoplastics polyolefin material. 10. An installation according to claim 4, wherein the edge portions of neighbouring sheet units in the solar power generating layer overlap each other.

11 . An installation according to claim 4, wherein the edge portions of neighbouring sheet units in the solar power generating layer are sealed together.

12. An installation according to claim 4, wherein at least a portion of the outer surface of the solar power generating layer is at an angle of at least 5 degrees to the horizontal.

13. An installation according to claim 4, wherein at least a portion of the outer surface of the solar power generating layer is at an angle of at least 15 degrees to the horizontal.

14. An installation according to claim 4, wherein at least a portion of the outer surface of the solar power generating layer is at an angle of at least 25 degrees to the horizontal. 15. An installation according to claim 4, wherein at least a portion of the solar power generating layer is substantially undulating.

16. An installation according to claim 4, wherein the mounds are each in the form of a hillock or hummock with elongate depressions between them.

17. An installation according to claim 4, wherein the mounds are each in the form of an elongate ridge with elongate depressions between them.

18. An installation according to claim 4, wherein each mound comprises a continuous or discontinuous layer of boulders and/or gravel, with a mean size of >1cm in diameter. 9. An installation according to claim 19, wherein the mean size is >20cm in diameter. >50cm in diameter or >100cm in diameter.

20. An installation according to claim 19, wherein the mean size is > 100cm in diameter.

21. An installation according to claim 4, wherein the installation is substantially mound-shaped.

22. An installation according to claim 4, wherein the surface of the solar power generating layer includes at least one furrow or channel which is inclined along at least part of its length.

23. An installation according to claim 4, wherein the capping support layer is built up to form an even terrain of raised ground higher than the perimeter or rim of the landfill at ground level. 24. An installation according to claim 4, wherein the installation has vertical porous or perforated riser shaft gas collection pipes or drill casings installed within at least one mound to collect landfill gasses from the underside of the solar power generating layer on the mound. 25. A method for constructing an installation for generating solar power according to claim 4, comprising constructing a capping assembly over a mass of decomposing material comprising the steps of

constructing a support structure which comprises at least two man-made mounds and covering it with a fluid-impermeable flexible sheet material, where said sheet material has solar power generating means bonded thereto, or the method comprises the further step of bonding said solar power generating means to the sheet material. .

26. A method according to claim 25, comprising covering the surface of the decomposing material with a capping support layer, and constructing the support structure on the capping support layer. 27. A method according to claim 25, comprising providing the capping support layer with a relatively even surface on which the capping assembly is laid down.

28. A method according to claim 25, wherein the solar power generating means comprises thin-film photovoltaic cells.

29. A method according to claim 28, wherein the thin-film solar photovoltaic cells are amorphous silicon or polycrystalline materials: cadmium telluride and copper indium gallium diselenide; or printed semiconductor thin-film photovoltaic cells

30. A method according to claim 27, wherein the solar power generating layer comprises a geomembrane. 31. A method according to claim 30, wherein the solar power generating layer comprises one or more of ethylene propylene diene terpolymer (EPDM); high density polyethylene (HDPE); flexible polypropylene (fPP), reinforced fPP-R; polyvinyl chloride (PVC): thermoplastics polyolefin, includng linear low-density polyethylene (LLDPE) and medium-density polyethylene (MDPE); polyurea, polyamide and polytetrafluoroethylene (PTFE); glass and bitumen- impregnated non-woven geotextile, or polyester reinforced thermoplastics polyolefin material.

32. A method according to claim 27, wherein the edge portions of neighbouring sheet units in the solar power generating layer are laid down to overlap each other.

33. A method according to claim 27, wherein the edge portions of neighbouring sheet units in the solar power generating layer are sealed together.

34. A method according to claim 27, wherein at least a portion of the outer surface of the solar power generating layer is configured at an angle of at least 5 degrees to the horizontal.

35. A method according to claim 27, wherein at least a portion of the outer surface of the solar power generating layer is configured at an angle of at least 15 degrees to the horizontal.

36. A method according to claim 27, wherein at least a portion of the outer surface of the solar power generating layer is configured at an angle of at least 25 degrees to the horizontal.

37. A method according to claim 27, wherein at least a portion of the solar power generating layer is configured to be substantially undulating.

38. A method according to claim 27, wherein the mounds are each constructed in the form of a hillock or hummock with elongate depressions between them.

39. A method according to claim 27, wherein the mounds are each constructed in the form of an elongate ridge with elongate depressions between them. 40. A method according to claim 27, wherein each mound is constructed to comprise a continuous or discontinuous layer of boulders and/or gravel, with a mean size of >1cm in diameter.

41. A method according to claim 40, wherein the mean size is >20cm in diameter.

>50cm in diameter or > 100cm in diameter.

42. A method according to claim 40, wherein the mean size is >100cm in diameter. 43. A method claim 27, wherein the installation is constructed to be substantially mound-shaped.

44. A method according to claim 27, wherein the surface of the solar power generating layer is configured to include at least one furrow or channel which is inclined along at least part of its length.

S 45. A method according to claim 27, wherein the capping support layer is built up to form an even terrain of raised ground higher than the perimeter or rim of the landfill at ground level.

46. A method according to claim 27, wherein the installation is provided with0 vertical porous or perforated riser shaft gas collection pipes or drill casings installed within at least one mound to collect landfill gasses from the underside of the solar power generating layer on the mound.

47. An installation according to claim 1 , wherein the solar power generating layer5 comprises a discontinuous sheet.

48. An installation according to claim 47, wherein the solar power generating layer comprises a number of sheet units or adjacent to each other to form a discontinuous layer and the edges of the sheet units comprised in the layer0 are bridged or held together by fluid-impermeable holding means.

49. An installation for generating solar power according to claim 48, comprising: a mass of decomposing material;

and a capping assembly, comprising

5 an optional base layer above the decomposing material, comprising a plurality of flexible sheet units of a fluid impermeable material, and

a solar power generating layer above the base layer, comprising a plurality of sheet units of a flexible fluid impermeable material with solar power generating means bonded thereto for producing electric power from sunlight0 incident on at least a portion of the installation,

wherein

5 in the solar power generating layer, the edge portions of neighbouring sheet units are adjacent and held together by the weight of a holding means above the edge portions to form a substantially fluid-impermeable solar power generating layer.

50 An installation according to claim 49, additionally comprising a capping support layer with a relatively even surface for supporting the base layer.

51. An installation according to claim 49, wherein said capping support layer is built up to form an even terrain of raised ground higher than the perimeter of the landfill at ground level.

52. An installation according to claim 49, wherein the capping support layer slopes down towards at least one point of the landfill perimeter.

53. An installation according to claim 49, wherein the base layer comprises a geomembrane.

54. An installation according to claim 53, wherein the base layer comprises one or more of ethylene propylene diene terpolymer (EPDM); high density polyethylene (HDPE); flexible polypropylene (fPP), reinforced fPP-R; polyvinyl chloride (PVC): thermoplastics polyolefin, includng linear low-density polyethylene (LLDPE) and medium-density polyethylene (MDPE); polyurea, polyamide and polytetrafluoroethylene (PTFE); glass and bitumen- impregnated non-woven geotextile, or polyester reinforced thermoplastics polyolefin material.

55. An installation according to claim 49, wherein the edge portions of neighbouring sheet units in the base layer overlap each and are held together by the weight of the overburden above the edge portions.

56. An installation according to claim 49 in which the edge portions overlap by 1 cm to 500 cm right angles to their edges.

57. An installation according to claim 49, wherein the overburden comprises at least one continuous or discontinuous layer of boulders and/or gravel.

58. An installation according to claim 57 where the boulders or gravel have a mean size of >1cm in diameter.

59. An installation according to claim 57 where the boulders or gravel have a mean size of >20cm in diameter.

60. An installation according to claim 57 where the boulders or gravel have a mean size of >50cm in diameter. 61. An installation according to claim 57 where the boulders or gravel have a mean size of > 100cm in diameter.

62. An installation according to claim 57, with rounded and/or porous structures comprising metal, wood, plastics or concrete on the surface of the overburden.

63. An installation according to claim 62 where the structures have a mean size of

> 1cm in diameter. 64. An installation according to claim 62 where the structures have a mean size of >20cm in diameter.

65. An installation according to claim 62 where the structures have a mean size of >50cm in diameter.

66. An installation according to claim 62 where the structures have a mean size of

> 100cm in diameter.

67. An installation according to claim 49 wherein the overburden extends over significantly all of the base layer.

68. An installation according to claim 49 additionally comprising a protective plastics layer between the overburden and the solar power generating layer.

69. An installation according to claim 68 wherein the protective layer and comprise one or more of polypropylene, polystyrene, acrylonitrile butadiene styrene, polyethylene terephthalate, polyester, polyamides, polyvinyl chloride, polyurethanes, polyvinylidene chloride, polyethylene, polytetrafluoroethylene or other plastics or polyolefin, polyurea, polyamide or polypropylene.

70. An installation according to claim 49 wherein the solar power generating means comprises flexible thin-film solar photovoltaic cells. 71. An installation according to claim 70, wherein the thin-film solar photovoltaic cells are amorphous silicon or polycrystalline materials: cadmium telluride and copper indium gallium diselenide; or printed semiconductor thin-film photovoltaic cells 72. An installation according to claim 49 wherein the solar power generating layer comprises a geomembrane.

73. An installation according to claim 72 wherein the solar power generating layer comprises one or more of ethylene propylene diene terpolymer (EPDM); high density polyethylene (HDPE); flexible polypropylene (fPP), reinforced fPP-R; polyvinyl chloride (PVC): thermoplastics polyolefin, includng linear low-density polyethylene (LLDPE) and medium-density polyethylene (MDPE); polyurea, polyamide and polytetrafluoroethylene (PTFE); glass and bitumen- impregnated non-woven geotextile, or polyester reinforced thermoplastics polyolefin material.

74. An installation according to claim 49 wherein the edge portions of neighbouring sheet units in the solar power generating layer overlap each other.

75. An installation according to claim 74 in which the edge portions of the solar power generating layer of individual solar caps overlap by 50cm to 500 cm at right angles to their edges.

76. An installation according to claim 49 wherein the edge portions of neighbouring sheet units in the solar power generating layer are sealed together by the holding means. 77. An installation according to claim 76 wherein the holding means comprises an upper part overlying a lower part, and the two parts sandwich and squeeze together edge portions of adjacent sheet units of the solar power generating layer (and optionally any protective layer) between them. 78. An installation according to claim 77 wherein each of the upper part and the lower part of the holding means is a laminar structure, and the two parts sandwich and squeeze together edge portions neighbouring sheet units of the solar power generating layer (and optionally any protective layer) between them.

79. An installation according to claim 77, in which either or both of the upper and lower parts comprises a mineral composite.

80. An installation according to claim 77 in which in either or both of the upper and lower parts the mineral composite is capable of adhering to the solar power generating layer to form a seal.

81. An installation according to claim 77 in which either or both of the upper and lower parts comprise a bitumen asphalt which is flexible.

82. An installation according to claim 77 in which in either or both of the upper and lower parts the bitumen asphalt is capable of adhering to the solar power generating layer to form a seal. 83. An installation according to claim 77 in which the mineral composite is a concrete or compacted hardcore aggregate.

84. An installation according to claim 77 in which either or both of the upper and lower parts comprise a rubber asphalt which is flexible.

85. An installation according to claim 77 in which in either or both of the upper and lower parts the rubber asphalt is capable of adhering to the solar power generating layer to form a seal. 86. An installation according to claim 77, in which the lower part rests on a laminar support layer comprising asphalt bitumen or another mineral composite.

87. An installation according to claim 77 wherein the holding means extends 30cm to 500cm in each direction beyond and at right angles to the edges of the solar power generating layer sheet units.

88. An installation according to claim 77 wherein the upper part of the holding means forms a pathway or roadway parallel to the edges of the sheet units of the solar power generating layer which it holds, and is 0.5m to 5m wide.

89. An installation according to claim 49 wherein the solar power generating layer is placed onto another support layer of asphalt bitumen. 90. An installation according to claim 49 wherein the lower part of the holding means extends under a part or all of the solar power generating layer.

91. An installation according to claim 77 wherein the lower part of the holding means comprises rubber asphalt.

92. An installation according to claim 49 wherein at least a portion of the outer surface of the impermeable solar power generating layer is at an angle of at least 3 degrees to the horizontal. 93. An installation according to claim 49 wherein at least a portion of the outer surface of the impermeable solar power generating layer is at an angle of at least 15 degrees to the horizontal.

94. An installation according to claim 49 wherein at least a portion of the outer surface of the impermeable solar power generating layer is at an angle of at least 25 degrees to the horizontal.

95. An installation according to any one of the claims 92 to 94, wherein the angle is measured at right angles to the long axis of an elongate holding means. 96. An installation according to claim 49 wherein at least a portion of the support structure for the solar power generating layer comprises a plurality of mounds, each bearing part of the solar power generating layer as a solar cap, and separated by elongate depressions, the bottoms of which are defined by elongate holding means.

97. An installation according to claim 96, wherein each mound comprises part of the overburden which comprises at least one continuous or discontinuous layer of boulders and/or gravel. 98. An installation according to claim 97 where the boulders or gravel have a mean size of > 1cm in diameter.

99. An installation according to claim 97 where the boulders or gravel have a mean size of >20cm in diameter.

100. An installation according to claim 97 where the boulders or gravel have a mean size of >50cm in diameter.

101. An installation according to claim 97 where the boulders or gravel have a mean size of > 00cm in diameter.

102. An installation according to claim 49, wherein each mound comprises rounded and/or porous structures comprising metal, wood, plastics or concrete on the surface of the overburden.

103. An installation according to claim 102 where the structures have a mean size of >5cm in diameter.

104. An installation according to claim 102 where the structures have a mean size of >20cm in diameter.

105. An installation according to claim 102 where the structures have a mean size of >50cm in diameter.

106. An installation according to claim 102 where the structures have a mean size of >100cm in diameter.

107. An installation according to claim 49, wherein any capping support layer and/or the overburden are so constructed that each elongate depression is aligned down at least one downwardly sloping surface towards the perimeter of the installation.

108. An installation according to claim 96, wherein each solar cap is provided with at least one secondary landfill gas collection means passing through the solar power generating layer and the protective layer and/or the lower part of the holding means according to claim 44, if present, and the solar cap mound to collect landfill gas from the decomposing material which passes through the base layer.

109. An installation according to claim 107 wherein the secondary gas collection means passes through the solar power generating layer at or near the highest point of the solar cap.

1 0. An installation according to claim 107 wherein the secondary gas collection means comprises at least one other collection means passing through the solar power generating layer at points lower than the highest point of the solar cap, and communicating with the collection means at or near the highest point of the solar cap.

1 11. An installation according to claim 107 wherein the secondary gas collection means is provided near its upper end with a pressure-sensitive gas release and flare-off device, such that in the event of the device detecting gas overpressure above a preset safe value beneath the solar cap on which it is mounted, it vents gas into the atmosphere and ignites it.

1 12. A method for constructing an installation according to claim 49, comprising covering a mass of decomposing material with a capping assembly, comprising

optionally laying a base layer above the decomposing material, comprising a plurality of flexible sheet units of a fluid impermeable material, such that the edge portions of neighbouring sheet units are adjacent;

laying sheet units of a solar power generating layer above the base layer, where said sheet material has solar power generating means bonded thereto, or the method comprises the further step of bonding said solar power generating means to the sheet material, such that the edge portions of neighbouring sheet units are adjacent and

laying holding means above the edge portions such that they are held together by the weight of the holding means to form a substantially fluid- impermeable solar power generating layer.

113. A method according to claim 112 further comprising the step of providing a support layer over the decomposing material, for supporting the capping assembly.

114. A method according to claim 112 further comprising the step of installing a protective layer above the overburden to protect the underside of the solar power generating layer.

115. A method according to claim 112 further comprising the steps of

preparing a plurality of mounds on or as part of the overburden, each mound being separated from each adjacent mound by a depression, prior to covering each mound with a sheet unit of the solar power generating layer, the edge portions of each sheet unit lying at the bottom of a depression adjacent to the edge portions of a neighbouring sheet unit, and then

applying holding means to the edge portions, so that they are held together by the weight of the holding means above the edge portions to form a substantially fluid-impermeable solar power generating layer.

1 16. A method for constructing an installation according to claim 76, comprising the step of covering a mass of decomposing material with a capping assembly, comprising

laying an overburden above the decomposing material to form a partially fluid-impermeable base layer;

applying the lower part of the holding means to at least some of the overburden; covering the holding means with the edge portions of sheet units of the solar power generating layer, such that the edge portions of each sheet unit lies adjacent to the edge portions of a neighbouring sheet unit, and then

117. An installation for generating solar power, comprising:

a mass of decomposing material; and

a capping assembly, comprising

optionally, a base layer above the decomposing material, comprising a plurality of flexible sheet units of a fluid impermeable material, and a solar power generating layer above the base layer, comprising a plurality of sheet units of a flexible fluid impermeable material with solar power generating means bonded thereto for producing electric power from sunlight incident on at least a portion of the installation,

wherein

in the base layer, if present, the edge portions of neighbouring sheet units are adjacent and held together by the weight of an overburden above the edge portions to form a partially fluid-impermeable base layer, and in the solar power generating layer, the edge portions of neighbouring sheet units are adjacent and held together by the weight of a the upper part of a holding means above the edge portions to form a substantially fluid-impermeable solar power generating layer, and

1 18. An installation according to claim 117, wherein the lower part of the holding means is fluid impermeable.

119. An installation according to claim 117 wherein the lower part of the holding means comprises a rubber asphalt.

120. An installation according to claim 117 wherein at least a portion of the solar power generating layer is substantially undulating, and comprises a series of mounds, each bearing the solar power generating layer as a solar cap, and separated by elongate depressions, the bottoms of which are defined by elongate holding means.

121. A method for constructing an installation according to claim 117,

comprising the step of covering a mass of decomposing material with a capping assembly, comprising

optionally laying a base layer above the decomposing material;

122. A method according to claim 121 , further comprising the step of providing a support layer over the decomposing material, for supporting the capping assembly.

123. A method according to claim 121 , further comprising the step of installing a protective layer above the overburden to protect the underside of the solar power generating layer. 124. A method according to claim 121 , further comprising

preparing a plurality of mounds on or as part of the overburden, each mound being separated from each adjacent mound by a depression, prior to

applying the lower part of the holding means to at least some of the depressions and mounds and covering at least some of the mounds with a sheet unit of the solar power generating layer, the edge portions of each sheet unit lying at the bottom of a depression on the lower part of the holding means and adjacent to the edge portions of a neighbouring sheet unit, and then

applying the upper part of the holding means if present to the edge portions, so that they are held together by the weight of the holding means above the edge portions to form a substantially fluid-impermeable solar power generating layer. 125. An installation for generating solar power according to claim 4 comprising:

a mass of decomposing material; and;

a capping assembly, comprising

126. A method of constructing an installation according to claim 125, comprising

covering a mass of decomposing material with a capping assembly, comprising laying a base layer above the decomposing material, comprising a plurality of flexible sheet units of a fluid impermeable material;

constructing a support structure which comprises at least two man-made mounds on the base layer; and