WO2010108969A1

WO2010108969A1 - Solar concentrator

Info

Publication number: WO2010108969A1
Application number: PCT/EP2010/053856
Authority: WO
Inventors: Fabio Marchetti; Renzo Verdolini
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-03-24
Filing date: 2010-03-24
Publication date: 2010-09-30
Anticipated expiration: 2011-09-24
Also published as: ITMC20090061A1

Abstract

A solar concentrator (1) comprises a box comprising a base (2) and a plurality of reflective clement (4) arranged within the box so as to concentrate the solar radiation on a receiver (5) located within said box, in position of the focus of these reflective elements (4).

Description

SOLAR CONCENTRATOR

This patent application for industrial invention relates to a high-efficiency solar concentrator. The Italian priority document MC200A000061 is incorporated by references.

Are known various types of solar concentrators fitted with a single reflecting element that concentrates sunlight on a receiver which is usually a pipe to produce hot water or one or more photovoltaic cells for producing electricity.

Where the receiver is a pipe or array of cells, the reflecting element is curved linear or semi-cylindrical so as to generate a focal axis on which the receiver is arranged linearly. Where the receiver is a single photovoltaic cell, the reflecting element has a semi-spherical or paraboloid so as to create a focal point where you placed the receiver.

It is to be considered that the cross-section profile of the reflecting item has the shape of a parabola. Therefore the receiver must be placed on the focus point of the parabola in which the sun rays reflected from the reflecting surface are concentrated.

This type of solar concentrators have a very limited power of reflection. As a result, to increase the power of reflection, large structures designed to maximize the reflecting surface are designed. However, increasing the size of the reflector, you increase the focus distance from the bottom of the dish reflector element (minimum point of the parabola). This solution involves great complications constructive, both for the excessive vertical space, both for the provision and support of the receiver at the focus of the parabola.

The patent US6,971 ,756 discloses an apparatus for concentrating the sun radiant energy to a receiver. This apparatus includes a plurality of concave reflective elements swivelly mounted on a frame. In this way, according to the position of the sun and then the direction of its radiation, each reflecting element is oriented so that its focus coincides with the location where the receiver is placed.

It is clear that the regulation of such an apparatus is extremely complex, as a result only some of the reflective items receive solar radiation and focus it on the receiver.

The object of the present invention is to eliminate the drawbacks of prior art, providing a solar concentrator that is able to provide a high yield.

Another aim of the present invention is to provide such a solar concentrator that is compact, versatile, economical and simple to make and assembly.

These aims are achieved according to the invention, with the characteristics listed in the annexed independent claim 1.

Advantageous embodiments are disclosed in dependent claims.

The solar concentrator according to the invention comprises a box comprising a base. A plurality of reflective elements are arranged within said box so as to concentrate the solar radiation on a receiver located within said box.

The shape and position of the reflectors are designed so that all reflecting elements can work simultaneously receiving the solar radiation and concentrating it on the receiver with no obstructions between them.

Additional features of the invention will appear clearer from the detailed description that follows, referring to purely illustrative and not limitative embodiments illustrated in the attached drawings, wherein: Figure 1 is a perspective view showing a first embodiment of the solar concentrator according to the invention, in which, for better clarity we have omitted some constructive elements;

Figure 2 is a schematic view illustrating the principle for the construction of the concentrator panels of Figure 1 ;

Figure 2A is an enlarged view of a detail of Figure 2;

Fig 3 is a cross-sectional view of the concentrator of Fig 1 ;

Fig 3A is an enlarged view of the detail enclosed in the circle (A) of Fig 2;

Figure 4 is a view like Figure 3 showing the angles of reflection of light; Figure 5 and a perspective view of a second embodiment of the solar concentrator according to the invention;

Figure 6 is a cross-sectional view of the solar concentrator of Figure 5, wherein the angles of reflection of light are shown;

Figure 7 is a perspective view of a third embodiment of the solar concentrator according to the invention;

Figure 8 is a cross-sectional view of the solar concentrator of Figure 7;

Figure 9 is a view like Figure 7 wherein the angles of reflection of light are shown;

Figure 10 is a perspective view of a fourth embodiment of the solar concentrator according to the invention;

Figure 1 1 is a cross-sectional view of the solar concentrator of Figure 10;

Figure 12 is a view like Figure 1 1 , wherein the angles of reflection of light are shown, and

Figure 13 is a view showing the cross section of four different types of concentrators, to highlight how varied the height of each concentrator having equal width.

With reference to Figures 1 to 4, a first embodiment of the solar concentrator according to the invention, indicated overall with the reference number (1 ) is described.

For now with reference to Figure 1 , the solar concentrator (1 ) includes a base (2) of substantially rectangular shape, suitable to be located on the ground.

A plurality of transversal walls (3) are mounted on the base (2). The transversal walls (3) stand at right angles from the base (2). By way of example, the concentrator (1 ) is provided with four transverse walls: two walls at the ends and two intermediate walls equidistant between them.

A plurality of longitudinal panels (4) are mounted between the transversal walls (3). Each longitudinal panel (4) is provided with a concave surface (40) in reflective material designed to reflect the sun rays. The reflective panels or reflector (4) are arranged symmetrically so that the concave surface (40) is directed inwards, i.e. towards the longitudinal axis of the concentrator (1 ).

In particular, the outer reflective panels are fixed on the edge of the base (2), while the other reflective panels are appropriately spaced from the base (2).

Each reflective panel (4) has a specifically designed curvature and arrangement in order to focus the reflection of sunlight on a common focal axis. A receiver (5) is placed in the common focal axis. The receiver (5) can be a pipe or tube. The water to be heated circulates into the tube (5). For this purpose, each transversal wall (3) has a hole (31 ) for the passage of the tube (5). The hole (31 ) is provided at the bottom and middle of each transverse wall (3).

Figure 2 shows a chart to explain how to select the curve and the layout of each reflector (4).

It shows a number of parabolas (A, B, C, D) stacked or nested one inside the other and having the same focal point (F) and the same vertical axis passing through the focal point (F). All the parabolas (A, B, C, D) are cut on top with an upper horizontal line (e). Only the outer parabola (A) is cut with a lower horizontal line (a) below the focal point (F); while the other parabolas (B, C, D) are cut with respective lower horizontal lines slightly above the focal point (F).

With reference also to Fig 2A, the parabola (B) is cut with a horizontal line (b), the parabola (C) is cut with a horizontal line (c) above the line (b) and the inner parabola (D) is cut with a horizontal line (d) below the line (b).

In this way eight segments (4A, 4B, 4C, 4D) are obtained, i.e. two segments for each parabola. The segments (4A, 4B, 4C, 4D) represent the cross- section profile of each reflector (4) and the position of each reflector (4) with respect to the base (2), the transversal walls (3), and the pipe (5), as shown in Figure 3. To be precise, the base (2) corresponds with the lower line (a) and pipe (5) is arranged with its axis coincident with the longitudinal axis passing through the focal point (F).

As shown in Figure 3A, for the assembly of reflectors (4) in the correct locations, each transversal wall (3) has grooves or channels (30) arranged according to the profiles (4A, 4B, 4C, 4D) to accommodate the edges of the reflectors.

In this way the reflectors (4) assumes the profiles (4A, 4B, 4C, 4D) and they are arranged symmetrically with respect to a vertical plane passing through the focal axis (F).

A plate (6) is arranged above the transversal wall (3) and reflectors (4). The plate (6) is made of a transparent material such as glass or poly-methyl methacrylate, to form a watertight box and protect the reflective surface (40) of the panels from damage due to bad weather or foreign objects.

As shown in Figure 4, the sun rays impact substantially in a vertical direction (I) on all reflectors (4). Each reflector (4) reflects the solar radiation concentrating the reflected rays (R) at the point of focus (F). Then each reflected radiation lies on a triangle with a vertex coincident with the focal point (F).

The distance between the bottom edge of each reflector (4B, 4C, 4D) and the base (2) is select so that the reflected radiation of the outer panel does not interfere with the respective inner panel. That is, the radiation reflected by panel (4A) does not interfere with the panel (4B), the radiation reflected by panel (4B) does not interfere with the panel (4C) and the radiation reflected by panel (4C) does not interfere with the panel (4D ).

As regards the method of assembly, with reference to Figure 2, the outer parabola (A) is calculated mathematically, deciding its size depending on the power to be achieved. Subsequently the trajectories of smaller parabolas (B, C, D) are calculated, leaving between two successive parabolas adequate space for the passage of sunlight. Clearly each parabola (A, B, C, D) must have the same focal point (F) and the same vertical axis.

To deliver the rays reflected from every parabola on the focal point (F) an arrangement is provided at the bottom of the inner parabolas, otherwise the reflectors hinder each others.

It then proceeds to cut the bottom of each parabola (B, C, D), in correspondence with the trajectory of the reflected rays of the larger parabola that precedes it.

The data and the trajectory obtained are stored in a CAD program by means of Cartesian coordinates X and Y. The CAD program will trace the drawing of each parabolic reflector. The CAD program is then converted into an executable file, for use as a path of working with a numerical control machine, such as a CNC milling machine, which performs the guide channels or grooves (30) and the hole (31 ) in each transversal wall (3). The edges of the reflectors (4) are inserted into the guide channels (30), and the reflectors (4) will take the shape of the profiles (4A, 4B, 4C, 4D) in accordance with design specifications. The tube (5) that is inserted into the hole (31 ) assumes the position of the focal axis (F).

The intermediate transversal walls (3) serve to prevent the bending of reflective panels (4) which tend to curve horizontally. Furthermore the intermediate transverse walls (3) eliminate the problems caused by the length of the reflective panels (4), which tend to bend longitudinally because of their small thin.

The reflective panels (4) may be reflective material such as steel or polished aluminum or they can be in any material coated with a reflective silver foil (40), commonly available on the market.

The solar concentrator (1 ) is closed and insulated by means of the transparent cover (6), so as to allow, especially in cold weather, an efficient heating of the liquid circulating within the tube (5).

The tube (5) preferably is a copper coil, placed around the focal axis (F). Thus, the concentrator (1 ) also allows for heating in winter, thanks to its compact structure with thermal insulation and its high efficiency because the reflected rays of all the reflectors (4) are concentrated in a single focal axis (F) in which the copper coil (5) is located.

Concentrator (1 ) can also be equipped with a solar tracker to allow the continued exposure to sunlight from dawn to sunset, to maximize performance.

Figures 5 and 6 show a solar concentrator (100) according to a second embodiment of the invention. The solar concentrator (100) is capable of concentrating sunlight into a focal point that can be occupied by a receiver (105), such as a photoelectric cell.

In this case, the concentrator (100) comprises a plurality of reflective elements (104A, 104B, 104C, 104D) in the shape of portions paraboloids of revolution cut on the top and bottom by horizontal planes. Again the concentrator (100) has reflecting elements with parabolic profiles in cross- section with the same focal point, the same vertical axis, and decreasing in size, stacked one inside the other.

It is important to note that the top and bottom of each portion of paraboloid (104A, 104B, 104C, 104D) is circular.

The assembly of the concentrator starts from a top panel (106) made of a transparent material. Guide channels, in the shape of concentric circles, are performed in the top panel (106). The upper edges of each reflector are fitted in these guide channels.

The lower edge of the outer reflector (104A) is connected to a circular base (102). A support (150) is mounted on the base (102). The support (150) supports the photoelectric cell (105), so as the photoelectric cell (105) is placed at the focal point (F) of each portion of the paraboloid.

The lower edges of the other portions of the paraboloid (104B, 104C, 104D) are located above the focal point (F) so as not to interfere with the reflected beam of the outer portion of the paraboloid, as shown in Figure 6.

Figures 7 to 9 shows a solar concentrator (200) according to a third embodiment of the invention.

The solar concentrator (200) comprises a parallelepiped box comprising a base (2), external longitudinal walls (201 ) and external and intermediate transversal walls (3). The concentrator (200) comprises a plurality of reflective panels (4A, 4B, 4C, 4D) with profiles shaped as portions of parabolas, and arranged symmetrically as shown in the first embodiment. I. e. the parabolas generating the panels (4A, 4B, 4C, 4D) all have the same focal point (F), the same vertical axis and they are of decreasing size stacked one inside the other and the receiver (5) is positioned in correspondence with the focal axis (F) of these parabolas.

However, we must consider that if there are a large number of reflectors, the rays reflected from outer reflectors do not reach the focal point (F), because they are shielded by their front panels. To solve said problem, more external reflectors (204A, 204B, 204C) have been added. The external reflectors (204A, 204B, 204C) have their focal points (Fl, F2, F3) below the base (2).

Respective lower reflectors (7A, 7B, 7C) are mounted below the external reflectors (204A, 204B, 204C). The lower reflectors (7A, 7B, 7C) have a slightly concave reflective surface oriented toward the focal axis (F). The lower reflective panels (7A, 7B, 7C) preferably are portions of branches of hyperbola with foci (Fl, F2, F3) coinciding with the foci of the respective upper panels (204A, 204B, 204C). So the lower reflectors (7A, 7B, 7C) are arranged in such positions as to receive radiation reflected from the outer longitudinal panels (204A, 204B, 204C), and concentrate the radiation on the point of focus (F). That is to say the concentrator (200) uses a double reflection that is focused on the point of focus (F).

A lower central panel (8) is designed to further improve the efficiency of the concentrator (200). The lower central panel (8) is placed beneath the focal point (F) to concentrate on the focal point (F) the direct rays of the sun that are not reflected by the other panels. The central panel (8) may have the profile of a portion of the parabola with focus (F), for example, the panel (8) can be a portion of the parabola generating panels (4A).

The inner panels (4A, 4B, 4C, 4D) may be omitted and the concentrator (200) can use only the double reflection of the side panels (204A, 204B, 204C) and lower panels (7A, 7B, 7C).

Figures 10 to 12 describes a solar concentrator (300) according to an embodiment of the invention.

The concentrator (300) has a plurality of lower reflectors (9, 9') with a concave surface upwards and outwards from the concentrator. The lower panels (9, 9') are arranged symmetrically with respect to a vertical plane passing through the receiver (5).

Each lower reflector (9, 9') reflects the sun rays on the convex surface of the respective upper reflectors (10, 10') arranged above the respective lower panel. All upper reflectors (10) disposed to the left of the focal point (F) directs the reflected radiation on the surface of a first central reflector (1 1 ') which focuses the radiation toward the focal axis (F) in which the receiver element (5) is located. All the upper reflective panels (10') arranged to the right of focal point (F) directs the reflected radiation on the surface of a second central reflector (1 1 ') which focuses the radiation toward the focal axis (F).

Lower longitudinal panels (9, 9') can have a cross-section profile shaped as a portion of the parabola with focus (Fc) above the respective upper panel (10, 10'). Accordingly, the upper panels (10, 10') have a profile shaped as a portion of the parabola with focus (Fc) coinciding with the focal point of the respective lower panel (9, 9').

The two central panels (1 1 , 1 1 ') are arranged above the focal point (F) and they have a rectilinear profile sloped of about 45 ° with respect to a horizontal line.

The concentrator (300) uses a triple reflection of the radiation, to maximize the efficiency of heating, because the surface of lower reflectors (9, 9 ') receiving the solar radiation is maximized.

Figure 13 shows a chart in which a prior art solar concentrator (400) is compared with solar concentrators according to the invention (1 , 200, 300).

All concentrators (400, 1 , 200, 300) have a width equal to (L). However, the bulk in the vertical direction of the concentrator (400) according to prior art is equal to 0.48 L, while the concentrators according to the invention (1 , 200, 300) have a considerably smaller bulk in the vertical direction. In particular, the triple-reflection concentrator (300) has a bulk of 0.08 L, that is six times smaller than the concentrator (400) according to the prior art.

Many changes and modifications of detail can be made to these embodiments of the invention within the reach of a person skilled in the art, however, falling within the scope of the invention expressed by the attached claims.

Claims

1 ) Solar concentrator (1 ; 100; 200; 300) comprising a box composed of a base (2) and a plurality of reflecting elements (4; 104A, 104B, 104C, 104D; 204A, 204B, 204C; 7A, 7B, 7C, 8; 9, 9\ 10, 10¹, 1 1 , 1 1 ) arranged in said box in such a way to concentrate solar radiation on a receiver (5; 105) arranged inside said box.

2) Concentrator (1 ; 100; 200) according to claim 1 , characterised in that said reflecting elements (4; 104A, 104B, 104C, 104D; 4A, 4B, 4C, 4D) have a cross-sectional profile as a portion of parabola, wherein the generating parabolas have the same focus (F), the same vertical axis and decreasing dimensions and the receiver (5; 105) is arranged in the focus (F) of said generating parabolas.

3) Concentrator (1 ; 200) according to claim 2, characterised in that said reflecting elements (4; 4A, 4B, 4C, 4D) are longitudinal panels arranged in symmetrical positions with respect to a vertical plane passing through the focal axis of the parabolas, with the borders of said reflecting panels (4) being fixed to transversal walls (3) of the box of the concentrator, wherein the two most external panels (4A) are in contact with the base (2); and the internal panels (4B, 4C, 4D) are spaced from the base (2) with lower border above a horizontal plane passing through said focus (F).

4) Concentrator (100) according to claim 2, characterised in that said reflecting elements (104A, 104B, 104C, 104D) are portions of paraboloids of revolution cut by an upper horizontal plane and a lower horizontal plane, the upper border of said reflecting elements shaped as a circumference being fixed to an upper transparent panel (106), wherein the most external element (104A) is joined to the base plane (102); and the internal elements (104B, 104C, 104D) are spaced from the base plane (102) with lower border above a horizontal plane passing through the said focus (F). 5) Concentrator (200) according to claim 1 , characterised in that it comprises:

- lateral reflecting panels (204A, 204B, 204C) with concave surface facing the said focus (F) in which the receiver (5) is provided and having a profile as portions of parabolas with corresponding foci (F1 , F2, F3) under a horizontal plane passing through the said receiver (5), and

- corresponding lower reflecting panels (7A, 7B, 7C) with a slightly concave upper side to receive the radiation reflected by said lateral panels (204A, 204B, 204C) and concentrate said radiation on said focal axis (F), said lower reflecting panels (7A, 7B, 7C) having a profile as a portion of branch of hyperbole with foci (F1 , F2, F3) coinciding with the foci of said lateral reflecting panels.

6) Concentrator (200) according to claim 3 or 5, characterised in that it comprises a lower central reflecting panel (8) arranged under the said focal axis (F) having a cross-sectional profile as portion of parabola with focus in said focal axis (F) to receive solar radiations directly and concentrate them on said focal axis (F).

7) Concentrator (200) according to claim 1 , characterised in that it comprises:

- lower longitudinal panels (9, 9') arranged symmetrically with respect to a vertical plane passing through the focal axis (F) in which said receiving element is provided, said lower longitudinal panels (9, 9') having a concave reflecting surface facing upwards and outwards with respect to said focal axis (F),

- upper longitudinal panels (10, 10') arranged before the focus (Fc) of the reflecting surface of said lower panels (9, 9'), said upper panels (10, 10') having a basically convex reflecting surface with focus (Fc) coinciding with the focus of the lower panels (9, 9') to receive the radiation reflected by the lower panels (9, 9'),

- two longitudinal central panels (1 1 , 1 1 ') arranged above said focal axis (F) to receive the radiation reflected by said upper panels (10, 10'), said central panels (1 1 , 1 1 ') having a flat reflecting surface and being arranged in oblique position with respect to a horizontal plane in such a way to concentrate radiation on the focal axis (F).