FR2951251A1 - Hybrid energy producing system, has thermal solar energy system provided with circulation pipe, and photovoltaic system provided with photovoltaic cell that is arranged in convergence place, of complementary radiation - Google Patents

Abstract

The system has a thermal solar energy system provided with a circulation pipe (100) for circulating coolant, and a photovoltaic system provided with a photovoltaic cell (200). An optical device (300) collects solar radiation and selectively directs a portion of the collected radiation towards the circulation pipe and another portion complementary to the collected solar radiation towards the photovoltaic cell. The photovoltaic cell is arranged in a convergence place, of complementary radiation, situated remotely from a pipe wall.

Description

i ENERGY PRODUCTION SYSTEM COMBINING THERMAL SOLAR ENERGY AND PHOTOVOLTAIC ENERGY

FIELD OF THE INVENTION The present invention relates to an energy production system comprising a solar thermal energy system and a photovoltaic system, wherein the solar thermal energy system comprises a conduit for the circulation of a heat transfer fluid and the system photovoltaic system comprises at least one photovoltaic cell.

BACKGROUND OF THE INVENTION Energy generation systems combining solar thermal energy and photovoltaic energy are the subject of important developments in order to increase the efficiency of these systems.

The advantage of these systems is to use the largest possible part of the solar light spectrum in the most efficient way and to generate electrical energy in a more or less direct way, or even complementarily. This type of system is particularly sought after to install power plants in remote areas in which no power network exists. Indeed, these power plants do not work at night, a supply of energy is necessary to start the thermal installation (pumps, turbines, etc.) in the morning. Photovoltaic electrical energy therefore allows, at daybreak, to deliver the energy required for start-up, thus avoiding a thermal energy storage installation, which would be costly and inefficient. Such hybrid systems therefore make it possible to create completely autonomous installations. However, combining these two techniques with satisfactory efficiency involves solving a number of problems.

In fact, with reference to FIG. 1, a solution considered for combining a solar thermal energy system and a photovoltaic system consists in arranging photovoltaic cells 1 on the walls of a duct 2 in which circulates a coolant, which is intended to to feed a turbine for example. A parabolic mirror 3 is furthermore arranged under the duct for reflecting and concentrating the sunlight towards the duct 2 and the active face 1A of the photovoltaic cells 1. In this configuration, the photovoltaic cells 1 must be designed to allow a portion of the radiation to pass through. (typically, long wavelength, that is to say greater than 500 to 800 nm approximately) to heat the fluid while absorbing the other part (of shorter wavelength, that is, that is, less than about 500 to 800 nm) to generate electricity. They must therefore be made of materials that are transparent to long wavelength radiation, which is particularly restrictive in terms of design, especially with regard to the formation of certain elements on the cell, such as, for example metallic materials that usually absorb long wavelengths. Moreover, to optimize the efficiency of the photovoltaic cells, they must be maintained at a moderate temperature, typically less than 50 ° C. Indeed, for most photovoltaic multi-junction cells, it is estimated that the efficiency decreases by 10/0 per ten ° C above the ambient temperature (i.e. 25 ° C) for which it has been optimized. However, the temperature of the fluid flowing in the duct greatly exceeds 100 ° C, and can reach 400 ° C. The temperature of the duct wall can exceed appreciably 50 ° C. It is therefore necessary to isolate the rear face (that is to say the face opposite to the active face) photovoltaic cells vis-à-vis the wall of the duct and / or evacuate the heat accumulated by the photovoltaic cells. For this purpose, it is known to metallize the rear face of the rear photovoltaic cells and fix at the rear thereof a cooler formed of metal and ceramic, such as a passive radiator for dissipating heat through fins.

However, such a cooling device blocks the long wave radiation which is necessary for heating the duct and is therefore not suitable for the system envisaged. It is also known from document US 2007/0289622 to have at the rear of the photovoltaic cell a conduit for the circulation of water, in order to evacuate the heat of the photovoltaic cell. The water thus heated can be used in a secondary system, for example a heating circuit of a building. However, because of the primary function of this water circuit, namely the cooling of the photovoltaic cell, it is excluded to bring it to temperatures above the boiling temperature of the water, and therefore it can not build a high-performance solar thermal system. A first object of the invention is therefore to propose a power generation system that optimally combines solar thermal energy and photovoltaic energy while allowing the photovoltaic cells to be cooled as well as possible. In particular, this system must make it possible to use photovoltaic cells comprising on their back side non-transparent materials with long wavelength radiation such as metals.

Another object of the invention is to minimize the cost of this system compared to the systems of the prior art.

BRIEF DESCRIPTION OF THE INVENTION In accordance with the invention, there is provided a system for producing energy comprising a solar thermal energy system and a photovoltaic system, in which: the solar thermal energy system comprises a duct for circulation of a heat transfer fluid, intended for example to feed a turbine, the photovoltaic system comprises at least one photovoltaic cell. Said system is characterized in that it comprises an optical device adapted to collect the solar radiation and to selectively direct the part of the solar radiation collected having a wavelength greater than a threshold wavelength towards the duct. and secondly the complementary portion of the solar radiation collected, having a wavelength less than said threshold wavelength, to the photovoltaic cell, and in that said photovoltaic cell is disposed at a convergence point of said complementary radiation located at a non-zero distance from the duct wall. The threshold wavelength, denoted As, is typically between 500 nm and 800 nm, and is preferably between 600 and 800 nm. Thus, in the present text, a so-called "long wavelength" radiation is defined which has a wavelength greater than λs and a complementary "low wavelength" radiation, ie have a wavelength less than λs. This optical device thus provides a decoupling of the radiation supplied to the conduit on the one hand and to the photovoltaic cell on the other hand, which makes it possible to move the photovoltaic cell away from the conduit and thus to overcome the problems associated with maintaining the at a moderate temperature. The distance between the photovoltaic cell and the duct wall is thus greater than 20 cm, and can reach several meters. This decoupling also makes it possible to overcome the constraint of the transparency of the photovoltaic cell with respect to the radiation necessary for heating the heat transfer fluid in the conduit. According to other features of the invention, which can be considered alone or in combination: the photovoltaic cell is disposed at the focal point of the optical device; Said optical device comprises a first mirror arranged between the photovoltaic cell and the duct with its concave reflecting face oriented towards the duct; said first mirror is a parabolic or cylindrical mirror reflecting all the light it receives; Said optical device further comprises a second mirror disposed between the first mirror and the duct with its convex reflecting face oriented towards the photovoltaic cell, and in that said second mirror is a dichroic mirror adapted to transmit the radiation having a wavelength greater than the threshold wavelength λ3 and for reflecting the complementary radiation; the second mirror has on its convex reflecting face a plurality of arches of convex curvature along the axis of the duct; the first mirror is pierced with at least one orifice to let the light reflected by the second mirror pass to the photovoltaic cell; said second mirror is disposed on the duct or incorporated in the wall of said duct; the photovoltaic cell comprises, on its rear face, a device for evacuating heat; - The optical device further comprises an optical element for homogenizing the light, disposed between the second mirror and the photovoltaic cell, so that said cell is uniformly illuminated; at least two photovoltaic cells are arranged in a discrete manner parallel to the conduit; the photovoltaic cell is arranged continuously parallel to the conduit.

BRIEF DESCRIPTION OF THE DRAWINGS Other features and advantages of the invention will emerge from the detailed description which follows, with reference to the accompanying drawings in which: - Figure 1 is a block diagram of a system according to the prior art; FIG. 2 is a block diagram in section of a preferred embodiment of the system according to the invention; FIG. 3 illustrates the reflection made by the first mirror; FIG. 4 illustrates the reflection made by the second mirror, according to a first embodiment; - Figure 5 illustrates the reflection performed by the second mirror according to a second embodiment.

It is specified here that, for reasons of clarity of the drawings, they do not respect the scale of the various components.

DETAILED DESCRIPTION OF THE INVENTION With reference to FIG. 2, the hybrid energy production system comprises, on the one hand, a solar thermal energy system comprising a conduit 100 for the circulation of a heat transfer fluid and, on the other hand, a photovoltaic system. comprising at least one photovoltaic cell 200. The two systems are coupled by means of an optical device 300 which will be described in detail below. The incident solar radiation is illustrated by a double arrow while the radiation transmitted to the photovoltaic cell is represented by a simple arrow and that transmitted to the conduit is represented by a dashed arrow. Solar thermal energy system The solar thermal energy system comprises a duct 100 in which circulates a heat transfer fluid, which feeds a turbine or any other appropriate device. The duct 100 in which the coolant circulates is generally of circular section and is surrounded by a vacuum envelope of circular section or optionally square. The conduit 100 is typically several meters long, for a diameter of about 10 cm. The duct 100 is made of a heat-conducting and dark-colored material, in order to absorb as much as possible of the long-wave solar radiation. The temperature of the fluid flowing in the duct 100 is generally between 100 and 400 ° C. The solar thermal energy system is known in itself and will not be described in more detail.

Photovoltaic system The photovoltaic system comprises at least one photovoltaic cell 200, disposed at a distance from the duct 100 with, in the example shown in Figure 2, its active face 201 facing the duct. The distance between the photovoltaic cell 200 and the wall of the duct 100 is at least 20 cm, but can reach several meters. In a manner known per se, the photovoltaic cell 200 comprises a stack of layers of semiconductor materials, such as silicon but, preferably, III-V or II-VI materials. This is usually a tandem type multi-junction cell.

Preferably, especially in the case where the photovoltaic cells are made of expensive materials, several photovoltaic cells 200 are distributed parallel to the conduit 100 at substantially regular intervals. The implementation of photovoltaic cells 200 distributed continuously parallel to the conduit 100 would indeed be particularly expensive.

However, in the case where the material of the photovoltaic cells is inexpensive (for example in the case of amorphous or crystalline silicon), it may be envisaged to produce a continuous photovoltaic cell parallel to the duct 100. This particular embodiment will be described in FIG. detail below with reference to Figure 5.

By way of example, in the case of discrete photovoltaic cells (see FIG. 4), these have an area of the order of a few mm 2 or a few cm 2 and are separated by intervals of the order of 20 to 30 cm. At the rear of the photovoltaic cell 200, that is to say on its face 202 opposite to the active face 201, is provided a heat-removal device 203, typically consisting of a finned radiator. This device 203 is intended to dissipate as much as possible of the heat absorbed by the photovoltaic cell under the effect of solar radiation, so that the temperature of the cell 200 does not exceed a temperature beyond which its effectiveness Degrades significantly.

Typically, the temperature of the photovoltaic cell is kept below about 50 ° C.

The choice of an appropriate device is within the reach of the skilled person. Optical device The optical device 300 is designed to collect solar radiation and selectively direct a portion of the solar radiation collected to the conduit 100 and the other portion of solar radiation collected to the photovoltaic cell 200. For this purpose, the device 300 comprises a first mirror 310 arranged between the photovoltaic cell 200 and the duct 100 with its reflecting face 311 facing the duct 100. The first mirror 310 has an elongated shape whose longitudinal axis 312 is parallel to the duct. Like the duct 100, the first mirror 310 may thus have a length of several meters. For reasons of dimensioning, it can be realized in the form of several mirrors each having a shorter length and arranged side by side along the duct 100.

The reflecting face 311 of the first mirror 310 is concave so as to concentrate the solar radiation towards the duct 100. It is typically a parabolic or cylindrical mirror, allowing a moderate concentration typically between 10 to 100 times, adapted to a simple and inexpensive realization of the mirror 310.

Thus, as can be seen in FIG. 3, the solar radiation is reflected longitudinally or unidimensionally, that is to say that all the reflected rays belong to a plane perpendicular to the longitudinal axis 312 of the first mirror 310 The first mirror 310 is advantageously provided with a solar tracker (not shown) which makes it possible to orient it optimally with respect to the position of the sun throughout the day. Said tracker acts along a single axis, in a direction perpendicular to the longitudinal axis 312 of the mirror 310. Thus, when the duct 100 and the mirror 310 are oriented in a north-south direction, the tracker moves the mirror 310 in a direction is West. The optical device 300 furthermore comprises a second mirror 320.

This second mirror 320 is disposed between the first mirror 310 and the duct 100 with its reflecting face 321 facing the photovoltaic cell 200. Said mirror 320 has the particularity of being a dichroic mirror adapted to transmit the radiation of longer wavelength to ets and to reflect the radiation of wavelength lower than λs. Thus, the radiation collected by the first mirror 310 is separated at the second mirror 320 so that: - the long-wave radiation of said radiation passes through the mirror 320 and is transmitted to the conduit 100 to heat the fluid who circulates there; for this purpose, the mirror 320 is advantageously located on the duct 100 or even incorporated in the wall 101 thereof; and the radiation of small wavelength of said radiation is reflected by the reflecting face 321 in the direction of the photovoltaic cell 200 which absorbs it. Moreover, in addition to this dual reflection and transmission function, the second mirror 320 is also able to concentrate (by a factor of 2 to approximately 20) the radiation reflected towards the cell 200, which makes it possible to reduce the dimensions of the photovoltaic cell 200 (which is the most expensive part of the system) and thus to propose a system at an affordable cost. This also makes it possible to produce photovoltaic cells having dimensions compatible with those of the substrates from which they are manufactured (for example, substrates of germanium or gallium arsenide of 10 or 15 cm in diameter). To concentrate this radiation towards the photovoltaic cell, the reflecting face 321 is convex.

Dichroic materials are known to those skilled in the art and are commercially available, for example from the company 3M. The threshold wavelength λs is a parameter dependent on the material of the dichroic mirror. For optimal use of solar radiation, the threshold wavelength 30 must be greater than 500 nm, and preferably between 600 and 800 nm. The threshold wavelength is chosen so that all the low wavelength radiation (or most of it) can be absorbed by the photovoltaic cell. The mirror 320 may be made to the desired shape by employing, for example, a hot forming technique from a sheet of said dichroic material. In the case illustrated in FIG. 4, where the photovoltaic cells 200 are distributed discretely along the duct, the reflecting face 321 has a second curvature making it possible to form a substantially conical light beam in the direction of the photovoltaic cell 200. More specifically, the reflecting face (which is the opposite face to the rear face 323 visible in Figure 4) has a first convex curvature between the points A and B which belong to a transverse plane, that is to say perpendicular to the axis 312 of the first mirror, and a second concave curvature between the points C and D which belong to a plane perpendicular to said transverse plane. Thus, the second mirror 320 is in the form of a succession of arches disposed along the conduit 100 and each located in line with a photovoltaic cell 200, each arch concentrating on the respective cell the short-length radiation of Thus, unlike the first mirror 310 which reflects the radiation in a monodimensional manner, the double curvature of the second mirror 320 allows a two-dimensional reflection of the radiation. In the case mentioned above in which a continuous photovoltaic cell is arranged parallel to the duct 100 (when the materials constituting it are inexpensive), it is not necessary that the mirror 320 has this second curvature. This configuration is illustrated in Figure 5 (on which the conduit has not been shown). In this case, the mirror 320 is a parabolic or cylindrical dichroic mirror, having a longitudinal axis 322 parallel to the longitudinal axis 321 of the first mirror 310, reflecting the low-wavelength radiation in a one-dimensional manner to the photovoltaic cell ( that is to say, as indicated above, that the rays reflected by the surface 321 of the mirror 320 belong to a plane perpendicular to the axis 322). The active face 201 of the photovoltaic cell 200 is disposed at a convergence point of said low wavelength radiation, preferably at or near the focal point of the second mirror 320. In order for the cell 200 to receive the radiation coming from the second mirror 320, the first mirror 310, which is interposed between the cell 200 and the mirror 320, must be pierced with an orifice 313 (visible in FIG. 2) allowing the passage said radiation. According to an advantageous embodiment of the present invention, the optical device 300 further comprises an optical member 330 for homogenizing the light, arranged between the second mirror 320 and the photovoltaic cell 200, so that said cell 200 is uniformly illuminated. .

The optical homogenizer may consist of a hollow reflective cylinder or a refracting solid glass cylinder. Example of embodiment As a guide but not limiting, we can size the system shown in Figures 4 and 5 as follows.

The opening of the first mirror 310 is chosen of the order of a few meters, for example between 1 and 5 meters. The opening of the second mirror 320 is chosen of the order of a few tens of centimeters, for example 10 to 50 cm. When, as in FIG. 4, discrete photovoltaic cells are used, each cell 200 has an area of a few cm.sup.2, or even a few mm.sup.2. In the case illustrated in FIG. 5, the continuous photovoltaic cell has a width of a few centimeters, or even a few millimeters, over a length of several meters, and can be obtained by the longitudinal juxtaposition of elementary cells each having a length of a few centimeters or tens of centimeters.

It goes without saying that the embodiments described here are only particular illustrations of the invention and that the skilled person can choose other shapes or dimensions of the components of the optical device without departing from the scope of the invention. present invention.

In particular, the optical device may comprise other elements, such as for example additional mirrors, which may involve a different orientation of the active face of the photovoltaic cell vis-à-vis the conduit.

Claims (14)

REVENDICATIONS1. Energy production system comprising a solar thermal energy system and a photovoltaic system, - the solar thermal energy system comprising a conduit (100) for the circulation of a heat transfer fluid, - the photovoltaic system comprising at least one photovoltaic cell (200), said power generation system being characterized in that it comprises an optical device (300) adapted to collect the solar radiation and selectively direct the part of the solar radiation collected having a wavelength greater than a threshold wavelength (As) towards the duct (100) and secondly the complementary portion of the solar radiation collected, having a wavelength less than said threshold wavelength (As), towards the photovoltaic cell (200), and in that said photovoltaic cell (200) is disposed at a convergence point of said complementary radiation located at a distance of the wall of the duct (100). 2. System according to claim 1, characterized in that the threshold wavelength (As) is between 500 and 800 nm, preferably between 600 and 800 nm. 3. System according to one of claims 1 or 2, characterized in that the distance between the photovoltaic cell (200) and the wall of the duct (100) is greater than 20 centimeters. 4. System according to one of claims 1 to 3, characterized in that the photovoltaic cell (200) is disposed at the focal point of the optical device (300). 5. System according to one of claims 1 to 4, characterized in that said optical device (300) comprises a first mirror (310) arranged between the photovoltaic cell (200) and the duct (100) with its reflecting surface ( 311), concave, facing the duct (100). 6. System according to claim 5, characterized in that said first mirror (310) is a parabolic or cylindrical mirror reflecting all of the light it receives. 7. System according to one of claims 1 to 6, characterized in that said optical device (300) comprises a second mirror (320) disposed between the first mirror (310) and the duct (100) with its reflective face (321 ), convex, oriented towards the photovoltaic cell (200), and in that said second mirror (320) is a dichroic mirror adapted to transmit the radiation having a wavelength greater than the threshold wavelength (As) and to reflect the complementary radiation. 8. System according to claim 7, characterized in that the second mirror (310) has on its convex reflecting face (321) a plurality of arches of convex curvature along the axis of the duct (100). 9. System according to one of claims 7 or 8, characterized in that the first mirror (310) is pierced with at least one orifice (313) to let the light reflected by the second mirror (320) to the cell photovoltaic (200). 10. System according to one of claims 7 to 9, characterized in that said second mirror (320) is disposed on the duct (100) or incorporated in the wall (101) of said duct. 11. System according to one of claims 1 to 10, characterized in that the photovoltaic cell (200) comprises, on its rear face (202), a device (203) for the removal of heat. 5 12. System according to one of claims 7 to 11, characterized in that the optical device (300) further comprises an optical member (330) for homogenization of the light, arranged between the second mirror (320) and the cell photovoltaic (200), so that said cell (200) is uniformly illuminated. 13. System according to one of claims 1 to 12, characterized in that at least two photovoltaic cells (200) are arranged discretely parallel to the conduit (100). 10 14. System according to one of claims 1 to 12, characterized in that the photovoltaic cell (200) is arranged continuously parallel to the conduit (100).