GB2478747A

GB2478747A - Solar energy collection devices

Info

Publication number: GB2478747A
Application number: GB1004355A
Authority: GB
Inventors: Richard James Boyle; Norman Cottington
Original assignee: Naked Energy Ltd
Current assignee: Naked Energy Ltd
Priority date: 2010-03-16
Filing date: 2010-03-16
Publication date: 2011-09-21
Also published as: GB201004355D0

Abstract

A solar energy collection device comprising a transparent tube casing 1, photovoltaic solar cells 4 and a thermal collector plates 8. The photovoltaic cells 4 and the thermal collector plates 8 are spaced apart, the thermal collector plates 8 also comprise a liquid circulation system having outlet and inlet ports 10, the ports being external to the transparent tube 1. The transparent tube 1 may be evacuated or filled with an inert gas, the photovoltaic cell 4 may also be semi-transparent. The tube 1 may also be rounded at one end with an end wall 2 at the opposite end, the end wall may also be sealed with an O-ring. The solar energy collection device allows for the photovoltaic cells 4 to be maintained at a low temperature so that they operate efficiently and the solar cells 4 do not need to be separately encapsulated from the atmosphere.

Description

SOLAR ENERGY COLLECTION DEVICES

This invention relates to solar energy collection devices and in particular to devices which convert solar energy into heat and electricity.

Conversion of solar energy into electricity is a well-practiced technique and, over recent years, major advances have been made in the production of photovoltaic arrays. These generally consist of semi-conductor materials appropriately encapsulated and adapted, when solar radiation falls on them, to generate electricity. The cost of such devices continues to fall due to increasing technological development and greater market size, leading to mass production benefits. However, much of the cost of producing such devices resides in the encapsulation required to prevent deterioration of the semi-conductor material, and that encapsulation additionally attenuates the amount of radiation falling on the semi-conductor material itself.

Separately, a variety of thermal collection devices is known which heat up when the sun shines on them and from which the heat may be extracted, either using heat pipes or a circulating liquid flow, usually water, though other materials such as glycol may be used in closed circulation systems.

Chinese Publication CN 1983640 discloses a combination device where a silicon photovoltaic array is attached to a metal heat collector bar. The metal heat collector bar has a heat pipe attached to it enabling thermal energy to be extracted from within a vacuum or nitrogen-filled tube surrounding the heat collector bar and the photovoltaic array. By means of appropriate sealed electrical leads, the electricity generated by the photovoltaic array can also be led outside the tube.

Chinese Specification CN 101025309 discloses a vacuum tube including a photovoltaic array and a heating panel which is set on a heat exchange inner glass pipe filled with heat-conducting medium. Again, the electricity is fed out from the device via sealed leads.

We have now found that composite structures of this nature suffer from a major disadvantage in that the temperature to which the photovoltaic array is subjected becomes too high for efficient operation.

According to the present invention, there is provided a solar energy collection device comprising an outer transparent tube and, sealed within it, one or more photovoltaic panels and one or more thermal collector plates, the photovoltaic panel(s) and the collector plate(s) being spaced apart from one another and the thermal collector plate(s) being in contact with a liquid circulation system having, external to the tube, inlet and outlet ports for liquid. By spacing the photovoltaic panel(s) and the thermal collector plate(s) apart, heat is not directly conducted from the collector plate(s) to the photovoltaic panel(s).

The interior of the tube, which is sealed, may be evacuated or may be filled with an inert gas, for example nitrogen. If the interior is under vacuum, the tube is preferably of circular section. It may be made of glass or plastics material.

A major advantage of this construction is that the cost of the photovoltaic panel or panels is reduced because the panels themselves do not have to be encapsulated. The vacuum or inert atmosphere protects the semi-conductor material of the panel from oxidation and other effects which would adversely affect its performance.

Preferably the photovoltaic array is a so-called semi-transparent photovoltaic array which, generally speaking, allows light of wavelengths 750 to 3000 nm to pass through it. The solar energy collection device is preferably oriented in use so that the photovoltaic panel or panels are towards the sun with the thermal collector plate accordingly behind them as seen from the direction of the sun.

Preferably the surface of the collector plate or plates facing the rear of the photovoltaic panel or panels is coated to be highly absorptive, i.e. so that it does not reflect incident radiation back on to the photovoltaic panels.

A particularly preferred arrangement is to include within the tube a single collector plate and two elongate photovoltaic panels set in V formation.

In operation, the fluid flow through the circulation system attached to the thermal collector plates may be arranged to ensure that the maximum operating temperature of the unit, and accordingly of the photovoltaic array(s), is kept below a level at which the photovoltaic efficiency would drop.

The invention is illustrated by way of example with reference to the accompanying drawings which show two alternative constructions for solar energy collection devices in accordance with the present invention. In each drawing, the device is shown in plan view and section.

Referring to both drawings, the energy capture components are located within a cylindrical tube 1 having a rounded end to the right as shown in the drawings and the left-hand end of which is sealed by an end wall 2. The interior of the tube is evacuated or filled with an inert gas. In the former case, it is important to ensure good sealing between the end wall 2 and tube 1.

This may be effected by welding, both for glass and plastics tubes, or by using a flexible adhesive. Alternatively, the end wall may be fitted to the end of tube 1 via an 0-ring seal -when the tube is evacuated, the external pressure holds tube 1 and end wall 2 firmly together.

An additional advantage of using an 0-ring seal when the tube is evacuated is that the resilience enables thermal expansion to be taken into account as the unit heats or cools, even if the tube is of glass and the end wall of plastics, metal or glass. The unit is also very easy to assemble.

Located within the tube 1 are photovoltaic arrays and a thermal collector plate. In Figure 1, a single, flat photovoltaic array 4 extends across a diameter of the tube while, in Figure 2, two photovoltaic arrays 5 and 6 are mounted as shown. In each case behind the photovoltaic array is a metal collector plate 8, parts of which are moulded around an elongate U-shaped tube 10 through which liquid may be circulated. The two legs of tube 10 are sealed to end wall 2 and, in use of the energy collection device, an appropriate working fluid, for example water, is circulated through tube 10 at an appropriate rate. The thermal energy captured by collector plate 8 heats the liquid as it flows through the device.

Also sealed into end wall 2 are a pair of contacts 14 which are connected via wires not shown to the photovoltaic array(s) and which may be connected to an appropriate electrical storage device. A short stub pipe 16 which is normally sealed is also sealed into end wall 2. Pipe 16 may be used if it is desired to purge the interior of the tube e.g. with an inert gas, or to re-establish a vacuum.

The tube is preferably evacuated to a pressure of around 1 0 mbar. We have found that reducing the pressure to this extent materially reduces convection up to around 65°C, while overheating of the photovoltaic arrays to above that temperature is normally avoided by the circulation of the fluid through tube 10. However, in case the fluid is not so circulated, for example if the system of which the tube forms a part is shut down, we have found that constructing the tubes in accordance with the invention reduces the so-called stagnation temperature, i.e. the temperature to which the tube can rise in bright sunshine. This may be up to 260°C with many vacuum tube devices sold for the purpose, but is usually only around 160°C for tubes in accordance with the present invention.

Claims

CLAIMS1. A solar energy collection device comprising an outer transparent tube and, sealed within it, one or more photovoltaic panels and one or more thermal collector plates, the photovoltaic panel(s) and the collector plate(s) being spaced apart from one another and the thermal collector plate(s) being in contact with a liquid circulation system having, external to the tube, inlet and outlet ports for liquid.
2. A device according to Claim 1 wherein the tube is sealed and its interior evacuated or filled with an inert gas.
3. A device according to Claim 1 or 2 wherein the photovoltaic array is a semi-transparent photovoltaic array.
4. A device according to any one of Claims 1 to 3 wherein the surface of the collector plate or plates facing the rear of the photovoltaic panel or panels is coated with a highly heat absorptive coating.
5. A device according to any one of Claims 1 to 4 wherein within the tube is a single collector plate and two elongate photovoltaic panels set in V formation.
6. A device according to any one of Claims 1 to 5 wherein the outer transparent tube is rounded at one end and has a transverse end wall sealed to its other end.
7. A device according to Claim 6 wherein the sealing is via an 0-ring and the tube is evacuated whereby to hold the end wall firmly to the tube.