FR2972530A1 - Device for measuring solar radiation focused toward linear receiver by e.g. linear type Fresnel reflector, in solar power station, has shield arranged to move away from photodetectors and to permit radiation to hit photodetectors - Google Patents

Abstract

The device (14) has a set of photodetectors (16) i.e. photodiodes, for receiving an individual elementary beam focused solar radiation. A processing unit (18) processes detection signals of the photodetectors. A protective shield (20) i.e. mirror, is arranged in front of the photodetectors. The shield is arranged to move away from the photodetectors to reflect a part of the focused solar radiation and to permit another part of the focused solar radiation to hit each photodetector. Independent claims are also included for the following: (1) an assembly comprising a solar power station (2) a method for mapping of reflectors in a solar power station.

Description

The invention relates to the field of solar power plants using reflectors for focusing the solar radiation to at least one receiver adapted to convert solar radiation into another form of energy, and more particularly a measuring device for measuring focused solar radiation in such a solar power station.

More specifically, the invention relates to a measuring device for measuring focused solar radiation in a solar power plant, of the type comprising a plurality of individual elementary photodetectors for receiving focused solar radiation and processing means for processing detection signals of the photodetectors. .

The measurement of focused solar radiation in a solar power plant is desirable primarily to determine the efficiency of the assembly including the reflectors and the receiver and to optimize their positions. Difficulty occurs when measuring focused solar radiation because of the localized focus of the focused solar radiation leading to high light intensity and high energy striking the measurement devices. Different techniques have been developed to deal with this problem. One technique uses a target placed in a focal region of a reflector next to the receiver and a CCD camera placed away from the target to take pictures of the target. Another technique uses a tool comprising a light-sensitive area that is placed in the focal region of a reflector adjacent to the receiver. The light-sensitive area may be presented as a row of photodiodes or alternatively in the form of an optical fiber bundle having inlet ends located adjacent to the focal region of the reflector and the ends of the output leading to a remote CCD camera. These techniques are disclosed in "Parabolic trough optical performance analysis techniques," E. Lüpfert et al., ISEC2005-76023, Proceedings of ISEC (International Conference on Solar Energy) August 6 to 12, 2005, Orlando, Florida . The object of the invention is to propose a measuring device that is cost-effective while allowing an accurate measurement of the focused solar radiation.

To this end, the invention proposes a measuring device of the type mentioned above, the measuring device comprising a light-reflecting protective shield arranged in front of the photodetectors, said protective shield being configured to remotely divert some of the radiation from the photodetectors. solar focus and allow a portion of the focused solar radiation to strike each photodetector through the protective shield. The light-reflecting protective shield configured to reflect a portion of the solar radiation and allow some of the solar radiation to pass through reduces the light intensity that strikes the photodetectors without affecting the measurement accuracy. The temperature of the measuring device is kept relatively low, thus allowing the use of low cost photodetectors and associated processing means. The measuring device is compact. In other embodiments, the measuring device comprises one or more of the following features, taken alone or in a technically feasible combination: the protective shield is a mirror; the protective shield comprises at least one light reflective layer for reflecting solar radiation, said layer being provided with openings to allow solar radiation to pass through the protective shield; the photodetectors are photodiodes; it comprises neutral density filtering means arranged to filter the rays of light passing through the protective shield; the filtering means are arranged behind the protective shield and in front of the photodetectors; the filtering means are composed of a plurality of neutral density filters individually associated with at least one photodetector; it comprises neutral density filters having different optical densities; it comprises cooling means for cooling the photodetectors; it comprises a heat sink supporting the photodetectors; it comprises ventilation means for forcing a flow of air in order to cool the photodetectors. The invention also relates to the use of a measuring device as defined above in a solar power station for measuring a solar radiation focused towards a receiver by a reflector.

The invention also relates to an assembly comprising a solar power station comprising a receiver for converting solar energy and at least one reflector for focusing solar radiation towards the receiver and a measuring device arranged as defined above for measuring the focused solar radiation. by the reflector (s) to the receiver.

The invention also relates to a method for mapping solar radiation focused in a solar power plant comprising a receiver for converting solar energy and at least one reflector for focusing solar radiation to the receiver, said method comprising the step of placing a device measurement as defined above for measuring the solar radiation focused by the reflector to the receiver at different locations along the receiver.

The invention and its advantages will be better understood on reading the following description, given purely by way of example and with reference to the following drawings, in which: FIG. 1 is a general schematic view of a solar power station and a measuring device according to the invention placed so as to measure a focused solar radiation in the solar power station; FIG. 2 is a schematic view of the measuring device of FIG. 1; and FIG. 3 is a partial view of the measuring device of FIG. 2. The solar power station 2, illustrated in FIG. 1, comprises a receiver 4 and a reflector 6 for reflecting and focusing an incident solar radiation beam IR into a beam of focused solar radiation FR to the receiver 4. The receiver 4 is a linear receiver extending in a longitudinal direction (perpendicular to the plane of Figure 1). It is suitable for converting solar radiation into thermal energy. It comprises a network of fluid circulation tubes 8 extending side by side in the longitudinal direction and a collection basin 10.

The tubes 8 are intended for the circulation of a thermal fluid. In operation, the thermal fluid flowing in the tubes 8 is heated by the focused solar radiation, thereby converting solar radiation into thermal energy. The solar power plant comprises means for exploiting the thermal energy accumulated in the thermal fluid. For this purpose, the thermal fluid is used directly as an active fluid to produce mechanical and / or electrical energy, for example in turbines. Alternatively, the tubes 8 are connected to a thermal fluid circuit of the solar power plant and the solar power plant further comprises a separate active fluid circuit and heat exchangers between the thermal fluid circuit and the active fluid circuit for transmitting heat from the thermal fluid to the working fluid, said active fluid being in turn used to produce mechanical and / or electrical energy, for example in turbines. Alternatively or optionally, the receiver 4 comprises means for converting solar radiation into electrical energy, such as photovoltaic cells. The basin 10 receives the tube network 8 inside and has an inlet opening. The basin 10 opens towards the reflector 6 so that a beam of focused solar radiation FR is directed towards the inlet opening of the basin 10 and inside the basin 10. The latter is intended to improve the collection from the focused solar radiation beam FR to the tubes 8. The reflector 6 is of the linear Fresnel type. It comprises a plurality of longitudinally elongate light reflector mirrors 12 arranged side by side. Each mirror 12 can pivot about a longitudinal axis and be driven to reflect incident solar rays reaching the mirror 12 to the receiver 4 during the movement of the sun. In larger known solar power plants, such mirrors 12 typically have a length of between 10 meters and 30 meters and a width of between 1 meter and 3 meters.

The reflector 6 typically provides a focusing ratio of 1: 80 to 1: 100 between the light intensity reaching the reflector 6 and the light intensity at the focal region of the reflector. The mirrors are schematically illustrated in Figure 1 in the form of flat mirrors. The mirrors can have any suitable shape. In one embodiment, each mirror 12 is of circular or parabolic cross-section, forming approximately a linear focal region and a focal length corresponding to the distance between the mirror 12 and the receiver 4. The reflector 6 is arranged on the ground to reflect a solar radiation mainly upwards and the receiver 4 is placed above the reflector 6. When present, the basin 10 is inverted and placed above the tubes 8 to collect a light beam from the reflector 6. FIG. 1 illustrates a measuring device 14 for measuring a focused solar radiation reflected by the reflector 6. The measuring device 14 is placed in front of the receiver 4 in the focused solar radiation beam FR. The measuring device 14 is placed next to the receiver 4. As illustrated in FIG. 2, the measuring device 14 comprises a plurality of distinct individual elementary photodetectors 16, processing means 18 for processing detection signals emitted by the sensors. photodetectors 16 and a protective shield 20 to protect the photodetectors 16.

The photodetectors 16 are photodiodes. They are arranged online. The processing means 18 comprise two circuit boards 22. Each photodetector 16 is connected via a respective connection 24 to one of the circuit boards 22. The protective shield 20 is placed in front of the photodetectors 16 so that the photodetector 16 receives the focused solar radiation through the protective shield 20.

The protective shield 20 is configured to remotely detract from the photodetectors 16 a first portion of the light rays of the focused solar radiation and to allow a second remaining portion of the light rays of the focused solar radiation to pass through the shield 20 to strike the photodetectors. 16. For this purpose, the protective shield 20 is a protective mirror having translucent zones 23 of localized light transmission distributed on the mirror in alignment with the photodetectors 16. Each translucent zone 23 allows the light to pass through the mirror in this area. At least one translucent zone 23 is provided for each photodetector 16.

As illustrated in FIG. 3, the protective shield 20 comprises a translucent support layer 24 and a light reflecting layer 25 deposited on one side of the support layer 24. The reflecting layer 25 is provided with openings 26 distributed over the reflective layer 25 and individually defining a translucent zone 23 of the protective shield 20.

In a preferred embodiment, the support layer is a glass layer and the reflective layer 25 is a metallization coating. The reflecting layer 25 is preferably laminated on the rear face of the support layer 24 facing the photodetectors 16. The reflecting layer 25 is thus protected by the support layer 24.

R1 light rays striking an ordinary area of the reflective layer between the apertures 26 are reflected away from the photodetector 16 while the rays of light R2 reaching the apertures 26 pass through the protective shield 20 and strike the underlying photodetectors 16 correspondents. Optionally, the measuring device 14 further comprises neutral density filtering means. The neutral density filtering means is arranged between the protective shield 20 and the photodetector 16 to filter the light rays passing through the protective shield 20 and striking the photodetector 16. The neutral density filtering means 28 comprises a density filter respective neutral 28 in alignment with each elementary photodetector 16.

The neutral density filtering means allows the light to pass through them to the photodetectors 16, while reducing the light intensity over a wide spectral band. The neutral density filtering means enable each photodetector 16 to remain unsaturated.

In one embodiment, the neutral density filters have different optical densities for the photodetectors 16, namely for each photodetector 16, which is useful, for example, if the spread of solar rationing at the level of the measuring device 14 varied. The intensity of light may be greater in the middle than on the sides. In this case, the neutral density filters in the middle have an optical density which is preferably higher than that of the neutral density filters on the sides.

The measuring device 14 further comprises cooling means 30 for cooling the photodetectors 16. The cooling means 30 comprise an elongated heat sink 32 supporting the photodetectors 16. The heat sink 32 is typically a support comprising fins to increase heat exchanges with the surrounding air.

The cooling means 30 comprise fans 34 for forcing a flow of air inside a housing 36 of the measuring device 14 containing the photodetectors 16 and the processing means 18. One or more fans 34 are provided. Two fans 34 are illustrated in FIG. 2. As illustrated in FIG. 3, the light intensity reaching the photodetectors 16 depends on the ratio of the light passing through the protective shield 20 and the incident light. This ratio depends on the diameter d of the apertures 26, the reflectivity of the reflective layer 25 and the optical density of the neutral density filters. In a preferred embodiment, these parameters are chosen so that the photodetectors remain at their linear unsaturated regime. For typical photodetectors, it is about 100 mW / cm2. The reflectivity of the reflective layer 25 is typically greater than about 90%, or even greater than about 95%. In operation, the measuring device 14 is placed in front of the receiver 4. The measuring device 14 is oriented so that the row of photodetectors 16 extends transversely to the longitudinal direction of the receiver 4, to measure a focused solar radiation in a transverse plane (plane of Figure 1) perpendicular to the longitudinal direction. The intensity of light measured by each photodetector allows a mapping of the focused solar radiation beam FR to determine the intensity of light reflected by the different portions of the reflectors. Differences in light intensity with respect to the ideal can occur due to incorrect positioning or incorrect orientation of one or more mirrors 12 or defects in the superficial shape of one or more mirrors of the reflector . Due to the significant focusing of the solar radiation by the reflector 6, the light intensity and the energy of the focused solar radiation beam FR are very high near the receiver 4. By reflexion of the measuring device 14 a part of the light, the protective shield 20 reduces the light intensity received by the photodetectors 16. It therefore reduces the heat stored by the measuring device 14. This allows the use of photodetectors 16 operating at relatively low temperature ranges instead of specific photodetectors adapted for high temperature. The same applies to the processing means 22. Thus, it is possible to obtain a reliable and accurate measuring device at low cost. The amount of light passing through the shield 20 can be easily tuned by selecting the appropriate neutral density filter. For reliable operation of the photodetectors and the electronic circuit, the temperature should ideally not exceed 60 ° C.

In order to map the reflector 6 and the receiver 4, several measurements of the focused solar radiation beam are made at different locations along the receiver 4 by moving the measuring device 14 along the receiver 4. Measures can also be taken behind the receiver 4 in case the receiver does not have a basin.

The measuring device of the invention is not limited to use in a solar power plant comprising a linear receiver and a linear Fresnel reflector as described above. The solar power plant may include a linear cylindrical or parabolic reflector. The solar power plant may include a primary reflector and a secondary reflector. The solar power plant may include a field of heliostats driven to reflect light to a receiver. The measuring device can be adapted in terms of shape for a different type of assembly, namely by modifying the array arrangement of the photodetectors. In an alternative embodiment, the photodetectors are arranged in a network of rows and columns to define a detection surface instead of a detection array.

Claims (14)

REVENDICATIONS1. A measuring device (14) for measuring focused solar radiation in a solar power plant, of the type comprising: a plurality of individual elementary photodetectors (16) for receiving focused solar radiation, and processing means (18) for processing optical signal signals; detecting photodetectors, wherein the measuring device comprises a light-shielding protective shield (20) arranged in front of the photodetectors (16), said shield (20) being configured to deflect photodetectors (16) by reflection of a portion of the solar radiation focused and to let a portion of the focused solar radiation hit each photodetector (16) through the protective shield (20). 2. Measuring device according to claim 1, wherein the protective shield (20) is a mirror. Measuring device according to claim 1 or 2, wherein the protective shield (20) comprises at least one light reflective layer (25) for reflecting the solar radiation, said layer being provided with openings (26) to enable the solar radiation to cross the protective shield (20). 4. Measuring device according to any one of the preceding claims, wherein the photodetectors are photodiodes (16). A measuring device according to any one of the preceding claims, comprising neutral density filtering means (28) arranged to filter the passing light rays (16) through the protective shield (20). 6. Measuring device according to claim 5, wherein the filtering means are arranged behind the protective shield (20) and in front of the photodetectors (16). The measuring device according to claim 5 or 6, wherein the filtering means is composed of a plurality of neutral density filters (28) individually associated with at least one photodetector (16). 8. Measuring device according to claim 7, comprising neutral density filters having different optical densities. 9. Measuring device according to any one of the preceding claims, comprising cooling means (32, 34) for cooling the photodetectors. 10. Measuring device according to any one of the preceding claims, comprising a heat sink (32) supporting the photodetectors. 11. Measuring device according to any one of the preceding claims, comprising ventilation means (34) for forcing a flow of air to cool the photodetectors. 15 12. Use of a measuring device according to any preceding claim in a solar power plant for measuring focused solar radiation reflected to a receiver by a reflector. 13. An assembly comprising a solar power plant comprising a receiver (4) for converting solar energy and at least one reflector (6) for focusing the sunlight towards the receiver, and a measuring device (14) according to one any of claims 1 to 11, arranged to measure solar radiation focused by the reflector or reflectors (6) to the receiver (4). 25 14. A method of mapping a reflector (6) in a solar power plant comprising a receiver (4) for converting solar energy and at least one reflector (6) for focusing sunlight to the receiver, comprising the steps of placing the measuring device (14) according to any one of claims 1 to 11 to measure the solar radiation focused by the reflector to the receiver at different locations along the receiver (4).