Cooling circuit for receiver of solar radiation

ES 2 363 701 T3

DESCRIPTION

Cooling circuit for a solar radiation receiver

The present invention relates to a receiver of a system for the generation of electrical energy from solar radiation.

Solar radiation-based electrical power generation systems typically include:

(a) a receiver including a plurality of photovoltaic cells that convert solar energy into electrical energy and an electrical circuit for transferring electrical energy production from the photovoltaic cells; ^Y (b) a means for concentrating solar radiation on the photovoltaic cells of the receiver.

By way of example, the means for the concentration of solar radiation can be a dish reflector that includes a parabolic array of mirrors that reflect solar radiation incident on a relatively large surface area of ​​the mirrors towards a relatively small surface area of photovoltaic cells.

In addition to the parabolic array of mirrors, the dish reflector described above may also include a secondary system of mirrors adapted for modifying solar radiation (such as a solar flux modifier).

Another, but not the only, means of concentrating solar radiation is an array of separate mirrors that are positioned to reflect solar radiation incident on a relatively large surface area of ​​the mirrors to a relatively small surface area of ​​the mirrors. Photovoltaic cells.

Document DE 44 05 650 C1 describes a solar energy generator that includes a solar energy collection system with a curved mirror that is positioned to receive the sun's rays.

A solar energy module is positioned at the focal point of the mirror and angled reflector panels project and direct the rays from the module within the range of the mirror. The solar energy module is filled with a cooling fluid that circulates by means of a pump through a tank.

GB 2 026 767 describes a concentrator solar array module having a metallic heat absorber with a flat mounting surface, a semiconductor spacer provided with a layer of insulating material for example in the form of silicon oxide on a surface that is attached to the mounting surface of the thermal absorber by means of a thermally conductive adhesive, a semiconductor solar cell welded to the spacer and a glass cover attached to the solar cell by an adhesive.

The glass cover is provided with a textured surface to diffuse the light that hits the solar cell.

The present invention relates more particularly, although by no means exclusively, to a large-scale electrical power generation system based on solar radiation of the type described above that is capable of producing substantial quantities of electrical power ready for conditioning up to minus 20 kW of standard 415 volt three-phase alternating current.

Applications for such large-scale electrical power generation systems include power supply in remote areas for isolated grids, grid-connected power, water pumping, telecommunications, crude oil pumping, water purification, and hydrogen generation.

A significant problem associated with the development of commercially viable solar radiation-based electrical power generation systems of the type described above is the long-term performance of materials and the structural integrity of system components made from those materials as a consequence. of:

(a) exposure to extremely high intensity solar radiation capable of producing high temperatures, for example temperatures considerably above 1000 ° C;

(b) cycles between high and low solar radiation intensities; and (c) the temperature variations between different parts of the structural components.

The receiver is an area of ​​particular importance in this regard.

Specifically, in solar-based large-scale electrical power generation systems of the type described above, photovoltaic cells are exposed to intensities of solar radiation at least 200 times the intensity of the sun during optimal operating conditions. Furthermore, photovoltaic cells are subjected to significant cycling between extremely high and low levels of solar radiation and variations in the intensity of solar radiation across the surface of the receiver.

ES 2 363 701 T3

An object of the present invention is to provide a receiver that is capable of long-term exposure to extremely high intensities of solar radiation, cycling between extremely high and low intensities of solar radiation, and temperature variations between different sections of the receiver components.

According to the present invention there is provided a system for the generation of electrical energy from solar radiation as claimed in Claim 1.

Applicant has discovered that the above-described receiver is capable of extracting significant amounts of heat generated by incident solar radiation in an efficient and reliable manner. Specifically, Applicant has discovered that the preferred embodiment of the receiver described in more detail below is capable of extracting up to 50 W / cm² of the exposed photovoltaic cell. Therefore, the receiver tackles the significant problem that a large part of the radiation incident on the receivers of a large-scale electrical power generation system based on solar radiation is not converted into electricity and manifests itself as heat. which reduces the efficiency of photovoltaic cells.

Furthermore, the modularity of the receiver addresses (at least in part) the problem that the optimal locations for large-scale solar power generation systems based on solar radiation tend to be in regions that are remote from major populations and centers of energy. manufacturing and therefore building systems in such remote locations presents significant difficulties in terms of transporting the equipment to the sites, on-site construction and ongoing maintenance (including rapid replacement of component parts) on-site.

Furthermore, the modularity of the receiver makes it possible to improve the manufacture of the receiver because the manufacture can be based on the repeated manufacture of a relatively large number of relatively small modules rather than a small number of large components.

Preferably during use a coolant maintains the photovoltaic cells at a temperature of no more than 80 ° C.

More preferably during use a coolant maintains the photovoltaic cells at a temperature of no more than 70 ° C.

It is particularly preferred that during use a coolant maintains the photovoltaic cells at a temperature of no more than 60 ° C.

It is more particularly preferred that during use a coolant maintains the photovoltaic cells at a temperature of no more than 40 ° C.

Each module includes a structure that supports the photovoltaic cells.

Preferably the support structure defines the path of the coolant flow for the extraction of heat from the photovoltaic cells.

Preferably the support structure includes:

(a) a cooling element that at least partially defines the flow path, a cooling element that is formed of a material having a high thermal conductivity; and (b) a substrate interposed between the cooling element and the photovoltaic cells, the substrate including a layer formed of a material that has a high thermal conductivity and is an electrical insulator.

Preferably the cooling element acts as a heat absorber.

The cooling element can be made of any suitable material of high thermal conductivity.

By way of example, the cooling element may be a metal or ceramic of high thermal conductivity.

Preferably the cooling element is made of copper.

Preferably the high thermal conductivity / electrical insulation layer of the substrate is formed of ceramic material.

Preferably the substrate includes a metallized layer interposed between the photovoltaic cells and the high thermal conductivity / electrical insulation layer.

Preferably the substrate includes a metallized layer interposed between the high thermal conductivity / electrical insulation layer and the cooling element.

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Preferably the cooling element includes a base, a wall that extends upward from the base and contacts the substrate, whereby the base, side wall, and substrate define a closed cooling chamber that is part of the flow path. of refrigerant.

Preferably the cooling element includes a series of separate platforms extending from the base and contacting the substrate in a central part of the chamber and defining therebetween channels for the flow of coolant from near the end of the chamber to near a opposite end of the camera.

Preferably the spaced platforms are parallel so that the channels are parallel.

With the arrangement described above there is direct thermal contact between the substrate and the coolant flowing through the coolant chamber (including the channels) and between the substrate and the side wall and the platforms. This construction provides an effective means for the transfer of heat from the photovoltaic cells through the substrate to the refrigerant. In particular, the side wall and platforms provide an effective means of increasing the available surface area of ​​contact with the refrigerant to improve heat transfer to the refrigerant. This is an important characteristic given the high levels of heat transfer that are required to maintain photovoltaic cells at temperatures below 80 ° C, preferably below 60 ° C, more preferably below 40 ° C. An additional advantage of the construction is that the side wall and the platforms allow lateral movement of the substrate and the cooling element - as is required in many situations to accommodate the different thermal expansions of the materials used in the construction of the modules. . The accommodation to different thermal expansions of such materials is an important aspect in terms of maintaining the long-term structural integrity of the modules. In this context, it is important to note that the high levels of heat transfer required to maintain photovoltaic cells at temperatures below 80 ° C result in considerable constraints on the selection of materials for the components of the modules. Consequently, the preferred materials for the different components of the modules and for the clamping of the different components of the modules are materials that have different thermal expansions. There are two aspects to the problem of material selection and heat transfer. One aspect is the material requirements of the module components, such as the substrate and the cooling element, to define the heat flow paths from the photovoltaic cells to the coolant flowing through the cooling chamber. The other aspect is the material requirements to contain the elevated hydraulic pressures within the freezing chamber that are required to maintain the flow of refrigerant through the freezing chamber at required levels. In particular, the second aspect is related to the selection of materials to achieve a sufficient fixing strength between the substrate and the cooling element.

Preferably the base includes a refrigerant inlet and a refrigerant outlet for supplying the refrigerant and withdrawing the refrigerant from opposite ends of the chamber, the opposite ends of the chamber forming manifolds.

The refrigerant inlet, refrigerant manifolds, refrigerant outlet, and refrigerant channels described above define the refrigerant flow path in the module support structure.

Preferably the ratio of the total width of the channels and the total width of the platforms is in the range of 0.5: 1 to 1.5: 1.

Preferably the ratio of the total width of the channels and the total width of the platforms is of the order of 1: 1.

Preferably the ratio of the height to the width of each channel is in the range of 1.5: 1 to 5: 1.

More preferably the ratio of the height to the width of each channel is in the range of 1.5: 1 to 2.5: 1.

It is particularly preferable that the ratio of the height and width of each channel is of the order of 3: 1.

The receiver includes the frame that supports the modules in an array of modules.

The support frame supports the modules so that the photovoltaic cells form an at least substantially continuous surface that is exposed to concentrated reflected solar radiation.

The surface can be flat, curved, or stepped in the Fresnel shape.

The support frame includes a refrigerant flow path that supplies refrigerant to the refrigerant inlets of the modules and withdraws the refrigerant from the refrigerant outlets of the modules.

Preferably the coolant is water.

Preferably the inlet temperature of the water is in the range of 20-30 ° C.

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Preferably the outlet temperature of the water is in the range of 25-40 ° C.

Preferably, the means for concentrating the solar radiation on the receiver is a plate reflector that includes an array of mirrors for the reflection of the solar radiation incident on the mirrors towards the photovoltaic cells.

Preferably the surface area of ​​the dish reflector mirrors that is exposed to solar radiation is substantially larger than the surface area of ​​the photovoltaic cells that is exposed to reflected solar radiation.

According to an aspect that does not form part of the present invention, there is also provided a photovoltaic cell module for a receiver of a system for the generation of electrical energy from solar radiation, the module of which includes: a plurality of photovoltaic cells, an electrical connection for transferring the electrical energy production of the photovoltaic cells, and a coolant flow path that is in thermal contact with the photovoltaic cells so that during use the coolant flowing through of the flow path cools the photovoltaic cells.

The preferred features of the module are as described above.

The present invention is further described by way of example with reference to the accompanying drawings, of which:

Figure 1 is a perspective view of a preferred embodiment of the system for generating electrical energy from solar radiation;

Figure 2 is a front view of the receiver of the system shown in Figure 1 illustrating the exposed surface area of ​​the photovoltaic cells of the receiver;

Figure 3 is a perspective view in partial section of the receiver with components removed to more clearly illustrate the refrigerant circuit that is part of the receiver;

Figure 4 is an enlarged view of the section of Figure 3 which is described by a rectangle;

Figure 5 is an exploded perspective view of a photovoltaic cell module that forms part of the receiver;

Figure 6 is a side elevation of the assembled photovoltaic cell module of Figure 5;

Figure 7 is a section along the line AA of Figure 6;

Figure 8 is an enlarged view of the recirculated B region of Figure 7; and Figure 9 is an enlarged view of the recirculated region C of Figure 7.

The electrical power generation system based on solar radiation shown in Figure 1 includes a parabolic array of mirrors 3 that reflect the solar radiation incident on the mirrors towards a plurality of photovoltaic cells 5.

Cells 5 are part of a solar radiation receptor that is generally identified by the number 7.

As described in more detail hereinafter, receiver 7 includes an integrated refrigerant circuit. The surface area of ​​the mirrors 3 that is exposed to solar radiation is substantially larger than the surface area of ​​the photovoltaic cells 5 that is exposed to reflected solar radiation. Photovoltaic cells 5 convert reflected solar radiation into direct current electrical energy. The receiver 7 includes an electrical circuit (not shown) for the output of electrical energy from the photovoltaic cells.

The mirrors 3 are mounted on a frame 9. The mirrors and the frame define a dish reflector.

A series of arms 11 extend from frame 9 to receiver 7 and locate the receiver as shown in Figure 1.

The system also includes:

(a) a support assembly 13 that supports the reflector plate and receiver in relation to a ground surface and for sun tracking movement; and (b) a tracking system (not shown) that moves the reflector plate and receiver as required to track the sun.

As indicated above, the receiver 7 includes a refrigerant circuit. The refrigerant circuit cools the photovoltaic cells 5 of the receiver 7 with a coolant, preferably water, to minimize the operating temperature and to maximize the performance (including the operating life) of the photovoltaic cells 5.

The receiver 7 is purpose built to include the refrigerant circuit.

Figures 3 and 4 illustrate the receiver components that are relevant to the refrigerant circuit. It does

Note that a number of other components of receiver 7, such as the components that make up the electrical circuit of receiver 7, are not included in the Figures for clarity.

Referring to Figures 3 and 4, receiver 7 includes a generally box-shaped structure that is defined by a hollow post assembly 15.

Receiver 7 also includes a solar flux modifier, generally identified by numeral 19, extending from a bottom wall 99 (as seen in Figure 3) of the box-like structure. Solar flux modifier 19 includes 4 panels 21 that extend from bottom wall 99 and converge with each other. The solar flux modifier 19 also includes mirrors 91 mounted on the inward facing faces of the panels 21.

The receiver 7 also includes an array of 1536 tightly packed rectangular photovoltaic cells 5 that are mounted in 64 square modules 23. The array of cells 5 can best be seen in Figure 2. The term "tightly packed" means that the exposed surface area of the photovoltaic cells 5 make up at least 98% of the total exposed surface area of ​​the matrix. Each module includes 24 photovoltaic cells 5. The photovoltaic cells 5 are mounted on each module 23 so that the exposed surface of the cell array is a continuous surface.

The modules 23 are mounted on the bottom wall 99 of the box-like structure of the receiver 7 so that the exposed surface of the combined array of photovoltaic cells 5 is a continuous plane.

The modules 23 are mounted on the bottom wall 99 so that lateral movement is possible between the modules 23 and the rest of the receiver 7. The lateral movement allowed aids in adaptation to the different thermal expansion of the components of the receiver 7.

As described in more detail hereinafter, each module 23 includes a refrigerant flow path. The refrigerant flow path is an integrated part of each module 23. The coolant flow path allows the coolant to be in thermal contact with the photovoltaic cells 5 and extract heat from the cells 5 so that the cells 5 are kept at a temperature of no more than 80 ° C, preferably no more than 60 ° C, more preferably no more than 40 ° C.

The refrigerant flow path of the modules 23 is part of the refrigerant circuit.

The refrigerant circuit also includes the hollow posts 15 described above.

Furthermore, the refrigerant circuit includes a series of parallel refrigerant channels 17 that form part of the bottom wall 99 of the box-like structure. The ends of the channels 17 connect to the opposite pair of lower horizontal posts 15 respectively shown in Figure 3. The lower posts 15 define an upstream manifold that distributes the coolant to channels 17 and a downstream manifold that collects the refrigerant from channels 17. The modules 23 are mounted on the bottom surface of the channels 17 and are in fluid communication with the channels so that the refrigerant flows through the channels 17 into and through the refrigerant flow path of the modules 23 and back. to the channels 17 and thereby cool the photovoltaic cells 5.

The refrigerant circuit also includes a refrigerant inlet 61 and a refrigerant outlet 63. Inlet 61 and outlet 63 are located on an upper wall of the box-like structure. Inlet 61 connects to adjacent upper horizontal post 15 and outlet 63 connects to adjacent upper horizontal post 15 as shown in Figure 3.

During use, refrigerant that is supplied from a source (not shown) flows through inlet 61 into upper horizontal posts 15 connected to inlet 61 and then down to vertical posts 15 connected to upper horizontal post 15 . The refrigerant then flows into the lower manifold 15 upstream and, as described above, along the channels 17 and the refrigerant flow paths of the modules 23 and into the lower manifold 15 downstream. The coolant then flows upward through the vertical posts 15 that connect to the lower manifold 15 downstream and into the upper horizontal post 15. The refrigerant is then discharged from the receiver 7 through the outlet 63. The refrigerant flow described above is illustrated by the arrows in Figures 3 and 4.

Figures 5 to 9 illustrate the basic construction of each module 23.

As indicated above, each module 23 includes an array of 24 tightly packed photovoltaic cells 5.

Each module 23 includes a substrate, generally identified by the number 27, on which the cells 5 are mounted. The substrate includes a central layer 29 of a ceramic material and outer metallized layers 31, 33 on the opposite faces of the layer. made of ceramic material 29.

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Each module 23 also includes a glass cover 37 that is mounted on the exposed surface of the photovoltaic cell array 5. The glass cover 37 may be formed to optimize the transmission of useful wavelengths of solar radiation and minimize the transmission of unwanted wavelengths of solar radiation.

Each module 23 also includes a cooling element 35 that is mounted on the surface of the substrate 27 that is opposite the photovoltaic cell array 5.

The size of the cooling element 35 and the material from which it is made are selected so that the cooling element 35 acts as a heat absorber. A preferred material is copper.

Additionally, the cooling element 35 is formed to define a series of flow paths for the coolant for cooling the photovoltaic cells 5.

Each module 23 also includes electrical connections generally identified by numeral 81 that form part of the receiver's electrical circuit and are electrically connected to photovoltaic cells 5 within the electrical circuit. Electrical connections 61 are positioned to extend from outer metallized layer 31 and through substrate 27 and cooling element 35. The electrical connections 61 are housed within sleeves 83 which electrically isolate the electrical connections.

The cooling element 35 includes a base 39 and a side wall 41 extending from the base 39. The upper edge 43 of the side wall 41 is physically adhered to the substrate 27. It can be seen in Figure 5 that the base 35 and substrate 27 define a closed chamber. The bases 39 include a refrigerant inlet 45 (Figure 4) and a refrigerant outlet (Figure 4). The refrigerant inlet 45 and the refrigerant outlet 46 are located in diagonally opposite corner areas of the base 39.

The cooling element 35 further includes a series of parallel platforms 47 (Figure 9) that extend upwardly from the base 39 and occupy a substantial part of the chamber. The upper surfaces of the platforms 47 physically adhere to the substrate 27. The platforms 47 do not extend to the ends of the chamber and these opposite end zones of the chamber define a refrigerant inlet manifold 49 and a refrigerant outlet manifold 51 . Platforms 47 extend side by side substantially across the width of the chamber. Gaps between adjacent platforms 47 define coolant flow channels 53.

It is evident from the above that the refrigerant inlet 45, the refrigerant manifold 49, the flow channels 53, the refrigerant outlet manifold 49, and the refrigerant outlet 46 define the refrigerant flow path of each module 23. .

The applicant has discovered that by selecting:

(i) the width of the platforms 47 and of the channels 53 so that the width ratio is of the order of 1: 1; and (ii) the height and width of the channels 53 so that the ratio between the height and the width is of the order of 2: 1;

it is possible to achieve a sufficient heat transfer from the photovoltaic cells 5 to the coolant to keep the photovoltaic cells 5 at a temperature of no more than 60 ° C where, otherwise, an uncooled module would be at temperatures that would clearly exceed 1000 ° C in view of the high intensities of solar radiation incident on the photovoltaic cells 5.

As indicated above, the construction of the cooling element 35 makes it possible to achieve the high levels of heat transfer that are required to maintain the photovoltaic cells 5 at temperatures of no more than 60 ° C and to adapt to the substantially different thermal expansion of the cooling element 35 and substrate 27 that would otherwise cause structural failure in modules 23. Specifically, there is a transfer of heat from the substrate 27 to the coolant through direct contact of the coolant with the substrate 27 and through the side wall 41 and the platforms 47. The construction of the platforms 47 as the means for defining the channels of flow 53 substantially increases the heat transfer contact surface area with the refrigerant. Specifically, platforms 47 provide an opportunity for heat transfer to the refrigerant through the sides and bottom of channels 53. Furthermore, the platforms 47 define a series of separate "fingers" and that arrangement makes it possible to adjust to the relative lateral movement of the substrate 27 and the cooling element 35 as a consequence of the different thermal expansion of the materials from which these components and the components are made. materials that bond these components by adherence.

Figure 4 illustrates the position of a module 23 on the bottom wall of receiver 7. With reference to Figure, the refrigerant inlet 45 opens into a refrigerant channel 17 of the refrigerant circuit and the refrigerant outlet diagonally opposite 46 opens into an adjacent refrigerant channel 17 of the refrigerant circuit.

During use, as indicated by the arrows in Figures 4 and 5, the refrigerant flows from a feed channel 17 into the inlet manifold 49 via the refrigerant inlet 45 and then flows

ES 2 363 701 T3 from refrigerant manifold 49 into and along the length of channels 53 to outlet manifold 51. Subsequently, the refrigerant flows from the chamber through refrigerant outlet 46 into adjacent channel 17.

Many modifications can be made to the preferred embodiment described above without departing from the spirit and scope of the present invention.

By way of example, while the preferred embodiment includes 1536 photovoltaic cells 5 mounted in 64 modules 23 with 24 cells per module, the present invention is not limited thereto and extends to any suitable number and size of photovoltaic cells and modules.

By way of further example, while photovoltaic cells are mounted so that the exposed surface of the cell array is a flat surface, the present invention is not limited thereto and extends to any suitable shaped surface, such as surfaces. curved or stepped.

By way of further example, while the preferred embodiment includes the receiver refrigerant circuit that is part of the receiver support frame, the present invention is not limited thereto and extends to arrangements in which the refrigerant circuit is not part. of the structural framework of the receiver.

By way of further example, while the preferred embodiment includes a series of parallel elongated platforms 47 extending between the ends of the freezing chamber, the present invention is not limited thereto and it is not essential that the platforms are parallel and is not It is essential that the platforms are elongated. Specifically, it is within the scope of the present invention that there are gaps in the platforms 47. The gaps in the platforms may be required in certain circumstances to improve the lateral flexibility of the cooling element 35 relative to the substrate 27.

By way of further example, while the preferred embodiment includes a dish reflector in the form of a parabolic array of mirrors 3, the present invention is not limited thereto and extends to any suitable means of concentrating solar radiation on a receiver.

By way of further example, while the preferred embodiment of the receiver is constructed from extruded components, the present invention is not limited thereto and the receiver may be made by any suitable means.