CH710014B1 - Parabolic solar collector. - Google Patents

Abstract

The parabolic solar collector according to the invention comprises a self-supporting sealed enclosure of symmetrical configuration, enclosing a tubular device (4) fixedly mounted inside said enclosure, its axis coinciding with the axis of symmetry of the enclosure (7) . A linear parabolic mirror (2) is rotatably mounted on the tubular device (4), its focus coinciding with the axis of symmetry of the enclosure (7). The parabolic mirror (2) is provided with an energy-autonomous orientation device (9). The invention also relates to a heat transfer fluid circuit and an installation for producing and / or storing thermal energy.

Description

Description

Field of the Invention The present invention relates to a parabolic solar collector comprising a linear parabolic mirror and a tubular device traversed by a heat transfer fluid is placed at the focus of the linear parabola so that the parabolic mirror concentrates the incident solar rays on the tubular device, and provides heat to the heat transfer fluid. The present invention relates more particularly to such a solar collector comprising a transparent and mechanically resistant external enclosure. The present invention relates to a photovoltaic solar collector as well as a solar thermal collector.

PRIOR ART [0002] Solar collectors are known which correspond to the definition given above. The patent document FR 2 568 991, in particular, describes a solar collection and storage device with a small footprint which comprises a linear parabolic mirror designed to pivot around a hollow pylon forming the rigid vertical axis of a tower. cylindrical, the base of which constitutes a technical room and a thermal storage space. The walls of the cylindrical tower are made of transparent plastic elements assembled between superimposed circular beams. The beams are themselves suspended from the pylon by a first series of tensioners and secured to the base of the cylinder by other tensioners. This known construction has certain drawbacks. On the one hand, the installation described is large, 6 meters in diameter and 20 meters high, which makes it difficult to integrate it into existing buildings and structures. In addition, the construction or mounting of such a solar collection and storage device obviously represents considerable work.

Brief description of the invention [0003] An object of the present invention is therefore to remedy the drawbacks of the prior art which have just been described, and in particular to provide a solar collector which is easy to install and uninstall, and which can even be transported in one piece without requiring disassembly. The present invention achieves this object by providing a parabolic solar collector according to claim 1 appended hereto.

According to the invention, the transparent enclosure is self-supporting. In other words, it is rigid enough to resist deformation and to ensure the structural integrity of the solar collector, even when it is detached from any support. It will be understood that an advantage of this characteristic is that the solar collector of the invention can be moved without it being necessary to disassemble it beforehand. Its maintenance and commissioning are therefore greatly facilitated. In addition, the tubular device is fixedly mounted inside the enclosure. It therefore does not rotate on itself, which greatly simplifies the connection of the circuits of the circuit for the heat transfer fluid. Finally, according to an advantageous variant of the invention, the tubular device passes through the enclosure from side to side, so that its two ends open out on either side of the solar collector. This last characteristic lends itself particularly well to the realization of installations comprising a plurality of solar collectors connected in the same circuit for heat transfer fluid.

The linear parabolic mirror is rotatably mounted on the tubular device. It is provided with an energetically autonomous orientation device arranged to lean mechanically on a fixed part of the installation. The possibility of rotation of the linear dish with respect to the tubular device is necessary to orient the mirror facing the incident solar rays. The rotation of the mirror can be very slow. According to the invention, the orientation device is arranged inside the enclosure and it is integral in rotation with the linear parabolic mirror. The orientation device is connected to a source of energy which is also contained inside the enclosure. This characteristic makes the orientation device autonomous. Advantageously, the energy source is also integral in rotation with the mirror so as to remain immobile relative to the orientation device. Thanks to this characteristic, the wiring of the orientation device can be particularly simple.

According to an advantageous embodiment of the invention, the external enclosure has an axis of symmetry and therefore has the shape of a solid of revolution. It will be understood that giving the enclosure a form of solid of revolution gives it greater rigidity. In addition, according to an advantageous variant of this embodiment, the tubular device is mounted concentrically with the axis of symmetry of the solid of revolution. Indeed, this arrangement makes it possible to limit the external dimensions of the enclosure as much as possible while retaining sufficient interior space for the linear parabolic mirror to be free to rotate.

According to a very advantageous variant, the enclosure has the shape of a solid of revolution closed at each of its ends by a flange. It will be understood that the solid of revolution forms with the two flanges an enclosure enjoying great structural stability. According to this variant, each flange also has a central opening arranged to allow the passage of one of the ends of the tubular device. Preferably, the opening of the flanges is further arranged to allow each end of the tubular device to be fixed to the enclosure. Thus, the tubular device is integral with the two flanges, which further strengthens the structure of the sensor. It will be understood that the transparent enclosure acts as a frame inside which all the rest of the construction is fixed.

Brief description of the figures [0008] Other characteristics and advantages of the present invention will appear on reading the description which follows, given solely by way of nonlimiting example, and made with reference to the appended drawings in which:

fig. 1 fig. 2A and 2B fig. 3A and 3B fig. 4A and 4B fig. 5 fig. 6A and 6B fig. 7 A and 7B fig. 8A, 8B and 8C fig. 9A and 9B fig. 10 is a perspective view showing a parabolic solar collector according to a particular embodiment of the invention, the solar collector being installed on a cradle made of metal tubes;

are schematic views, respectively in perspective and from the front, of the transparent cylindrical enclosure of the solar collector of FIG. 1;

are schematic diagrams showing the linear parabolic mirror of the solar collector in fig. 1 respectively in perspective and in cross section, and illustrating how a linear parabolic mirror can focus the incident solar rays on the linear focus of the parabola;

are schematic sectional views showing the tubular device of the solar collector of fig-1;

is a partial sectional view showing more particularly the fixing of the tubular device to the enclosure of the solar collector of FIG. 1;

are views, respectively in perspective and from the front, showing how, in the solar collector of FIG. 1, the linear parabolic mirror is pivoted on the tubular device using two radial bearings, each radial bearing being fixed to the parabolic mirror by one of its ends;

are schematic views, respectively in perspective and in cross section, similar to FIGS. 6A and 6B, but also showing the external enclosure and the device for orienting the mirror;

are schematic sectional views corresponding to three particular orientations of the linear parabolic mirror and illustrating for each orientation the reflection of the incident solar rays;

are schematic plan views of two circuits for heat transfer fluid each integrating a set of parabolic solar collectors identical to that of FIG. 1. Figs. 9A and 9B respectively showing the various sensors connected in parallel and in series;

is a perspective view showing the series connection of solar collectors identical to that of FIG. 1.

Detailed description of an embodiment [0009] FIG. 1 is a perspective view showing a parabolic solar collector 1 according to a particular embodiment of the invention. It can be seen in the figure that the sensor is housed in a transparent protective enclosure 7. The protective enclosure is designed to enclose and protect all the sensitive and fragile parts of the solar collector. In the illustrated embodiment, the protective enclosure 7 has a cylindrical shape and is preferably made of glass. The cylindrical shape gives the enclosure good structural stability, and this stability is increased by the presence of two glass flanges 10 and 11 which are glued to the two ends of the cylindrical tube. We can also see that the two flanges have their center crossed by a tubular device 4 which is concentric with the axis of symmetry of the cylinder. The tubular device 4 is designed to be traversed by a heat transfer liquid (not shown). Fig. 1 still shows in transparency, inside the enclosure, a linear parabolic mirror 2 which is rotatably mounted on the tubular device 4, two counterweights 17 for the rotating mirror, and an energetically autonomous orientation device 9 which is carried by the parabolic mirror. In the illustrated embodiment, the orientation device is equipped with a wheel arranged to bear on the interior surface of the enclosure 7. It will however be understood that, according to other embodiments, the orientation device could be supported by another fixed part of the installation. In particular, it could rest on the tubular device 4. In this case, the rotational movements of the parabolic mirror relative to the tubular device could advantageously be produced by an ultrasonic motor similar to those which are commonly used in the autofocus devices of some cameras. Finally, it will be noted that the solar collector 1 is illustrated in a horizontal position, supported by a cradle made of metal tubes 20. However, it will be understood that the solar collector according to the invention can operate in all orientations (horizontal, vertical, inclined).

Figs. 2A and 2B are schematic views of the transparent cylindrical enclosure 7 of the solar collector. As already mentioned, in the illustrated embodiment, the protective enclosure consists of a glass tube of cylindrical shape, the two ends of which are closed by flat circular flanges 10 and 11 also made of glass, which are assembled by gluing to the cylinder. The connection of the flanges and the cylinder is protected by two metal flanges 21 which are bonded to the flanges and to the cylinder by means, for example, of a silicone sealant. These flanges also make it possible to secure the solar collector to a support (the cradle 20 in fig. 1 for example). The center of the flanges 10 and 11 is used for fixing the tubular device 4. In the example illustrated, this fixing is carried out by an aluminum flange 22. The glass used for the protective enclosure 7 (including the flanges 10 , 11) should preferably be as transparent as possible, offering the best transmittance of the radiation over a wavelength range from 250 to 2500 nanometers. From a transmittance point of view, calcium fluoride glass is one of the most suitable, but it is expensive. Quartz glass is almost as good and cheaper. We can also consider borosilicate.

The enclosure 7 of the solar collector is preferably waterproof. However, it will be understood that the interior of the enclosure is subjected to temperatures higher than the outside temperature during the operation of the solar collector. Therefore, pressure differences between the inside and outside of the enclosure are inevitable. These differences could theoretically shatter the glass enclosure. Several alternative variants can be envisaged to overcome this difficulty. First, in accordance with the embodiment illustrated in the figures, the enclosure can be fitted with two safety valves. A first valve to limit overpressures inside the enclosure and a second valve in the event of overpressure outside the enclosure. According to an alternative variant, one could provide an expansion membrane mounted on the enclosure. It will further be understood that no means of pressure equalization is really necessary, provided that the enclosure is sufficiently solid. In the same vein, we could still create a partial vacuum inside the enclosure, so that the pressure difference is always in the same direction.

Figs. 3A and 3B have schematic views, respectively in perspective and in cross section, of the linear parabolic mirror of the solar collector. A particularity of the linear parabolic mirror of the embodiment of the solar collector which is the subject of the present example is that the linear focus of the parabola coincides with the axis of symmetry of the protective enclosure 7.

The linear parabolic mirror 2 must have a weight as low as possible so as to limit the consumption of electrical energy necessary to control its orientation. Figs. 3A and 3B illustrate an example of construction of the linear dish. According to this example, the linear dish 2 consists of an aluminum sheet whose thickness can be 0.2 mm. The aluminum sheet is given its parabolic shape by stamping. The back of this sheet can be stiffened by arches 23 made of injected and machined aluminum. The arches are assembled to the sheet metal, for example by gluing, and make it possible to guarantee the holding of the parabolic shape. The concave part of the linear parabola 2 has a surface which must ensure the reflection of solar radiation towards the linear focus. By way of example, a parabolic mirror produced as explained above and having a reflecting surface of 0.575 m ² weighs approximately 680 grams.

Figs. 4A and 4B are schematic sectional views showing in detail the tubular device 4 of the solar collector

1. The main role of the tubular device is to transform the energy of solar radiation into thermal energy. The circulation of a heat transfer fluid (not shown) through the tubular device allows this energy to be transported outside the solar collector to be used. As already mentioned, the tubular device is arranged concentrically with the linear focus of the parabolic mirror 2. When the dish is well oriented, it therefore concentrates the solar radiation on the tubular device. In a manner known per se, the latter may comprise an absorption tube 25 made of metal (for example stainless steel) covered with a layer promoting the absorption of light energy (for example a treatment with black chromium) , and a glass insulation tube 26 closed at its two ends and which surrounds the absorption tube. A high vacuum is created in the volume formed between the absorption tube 25 and the insulation tube 26 so as to create very good insulation between the absorption tube and the outside. In the example illustrated, it will be noted that the glass insulation tube 26 is closed at one of its ends by a flange 27. In addition, in order to make it possible to balance the difference in expansion between the insulation tube 26 and the absorption tube 25, the other end of the glass tube is closed by a compensator 28.

[0015] FIG. 5 is a partial sectional view showing more particularly the fixing of the tubular device 4 to the glass flange 10 of the enclosure 7 of the solar collector. We can see in fig. 5 that, in the example illustrated, the fixing of the tubular device 4 to the flange 10 is carried out by an aluminum flange 22, the flange 22 is glued to the glass flange 10 by means of a silicone sealant supporting the high temperature (~ 200 ° C). This flexible bonding makes it possible to reduce the stresses linked to the difference in expansion between glass and aluminum. The link between the glass flange 10 and the insulation tube 26 of the tubular device 4 is produced by O-rings 29, that is to say O-rings, supporting the high temperature (~ 200 ° C and in Viton for example). A small compression flange 30 made of aluminum allows, by means of mechanical tightening, to compress the O-ring 29 so as to center and fix the insulation tube 26 while allowing to ensure a certain flexibility of the assembly and sealing. The assembly is constructed so as to create a cold bridge between the interior of the protective enclosure 7 and the exterior so as to evacuate a little heat from the interior of the protective enclosure towards the exterior , in order to limit the temperature inside the protective enclosure.

Figs. 6A and 6B are views, respectively in perspective and from the front, showing how the linear parabolic mirror 2 is pivoted on the tubular device 4 using two radial bearings 12. The parabolic mirror 2 can rotate around the tubular device over 360 °. To this end, the two radial bearings each include a ball bearing. These bearings allow the rotation of the linear dish and positions it precisely in relation to the tubular device during its entire rotation. The movable external part of the ball bearings is integral with the linear dish. The inner part is, when it is clamped on the glass insulation tube 26 of the tubular device by means of O-rings giving this connection a certain flexibility. One of the two ball bearings has a radial holding function. As for the other, it must provide a radial and axial holding function. Indeed, the solar collector should preferably be able to operate in all positions, from horizontal to vertical. One of the two ball bearings is arranged to compensate for the differences in expansion between the insulation tube (glass) and the linear dish (aluminum).

Figs. 7A and 7B are schematic views similar to FIGS. 6A and 6B, but which also show the external enclosure 7 and the orientation device 9 of the mirror 2. To orient the parabolic mirror 2 perpendicular to the solar radiation, it is necessary to pivot the mirror relative to the fixed parts of the sensor solar 1. In the present example, the angular displacement of the mirror is ensured by an electric motor which is part of the orientation device. The electrical energy consumption of this engine should be as low as possible. As already mentioned, the parabolic mirror is pivoted by means of the radial bearings 12 which are fitted with ball bearings. Ball bearings require very little energy to "take off" during start-up, which ensures precise rotation.

It is absolutely necessary to avoid introducing materials liable to evaporate inside the protective enclosure 7, since the vapors then condense on the inside of the protective enclosure, on the reflective part. of the dish 2 and on the insulating tube 26 made of glass, which risks reducing the efficiency of the sensor. We therefore preferably use ball bearings which can operate dry, that is to say without grease or oil. Remember that these ball bearings rotate very slowly, in principle one rotation per day. Preferably, the main parts of the radial bearings 12 are made of aluminum. However, to avoid corrosion problems, the bearing balls are preferably glass, not steel. Indeed, steel and aluminum do not mix well (problem of electrochemical corrosion).

It will be understood that the linear parabolic mirror 2 is not balanced with respect to its axis of rotation. To simplify the orientation system, optimize its consumption of electrical energy and increase its precision, it is useful to balance the linear dish and bring the center of gravity of the assembly on the axis of rotation, therefore on the axis of symmetry of the protective enclosure. In the example illustrated, counterweights 17 are used to balance the mirror. The protective enclosure 7 being cylindrical, its volume makes it possible to place the counterweights opposite the parabola 2. The parabola being of very light construction, its orientation system being very small, the mass of the counterweights 17, respectively their volume, will be low. The counterweights can be made of steel, a material much denser than aluminum, and they are preferably placed very close to the inner surface of the protective enclosure so as to maximize the lever arm. It will also be noted that in the example illustrated, the counterweights 17 are also used to accommodate two small solar cells which allow the supply of electricity to the orientation device 9. This location is very favorable for solar cells, because they are thus always oriented perpendicular to solar radiation.

Figs. 8A, 8B and 8C are schematic sectional views showing three particular orientations of the linear parabolic mirror 2 and illustrating for each orientation the reflection of the incident solar rays. The solar collector is designed to collect solar energy. If for any reason it is decided to stop the production of energy, the linear parabolic mirror 2 can be rotated so as to no longer concentrate the solar radiation on the tubular device 4, which will have the effect of stopping the production of energy . To do this, it suffices to provide management electronics (not shown) for controlling the orientation device 9 (FIG. 7B) so that it orients the linear parabola so that it no longer focuses the radiation. solar on the absorption tube 25 (fig. 4B).

In the illustrated embodiment, the orientation device 9 is not connected to the outside of the enclosure 7 by wiring. However, it is possible to provide a radio system (for example according to the Bluetooth® standard) for communicating from the outside with the electronic management of the orientation device 9. Under these conditions, the electronic management system must be equipped with a receiver. It is preferably also equipped with a transmitter for sending information concerning the solar collector, for example reporting a malfunction.

The tubular device 4 of a solar collector 1 according to the invention is intended to be traversed by a heat transfer fluid

5. For this purpose, the absorption tube 25 of the tubular device 4 of at least one solar collector 1 must be integrated into a circuit 6 for heat transfer fluid. The number of solar collectors in which the absorption tubes are part of the same circuit for heat transfer fluid is not theoretically limited. Tubular devices, or more precisely their absorption tubes, can be connected in series, in parallel or a mixture of both. It will be understood that each solar collector 1 is arranged to supply heat to the heat transfer fluid 5 which runs through the tubular device 4. FIG. 9A schematically illustrates a circuit 6 for heat transfer fluid 5 associating five solar collectors 1 connected in parallel. Fig. 9B schematically illustrates a circuit 6 for heat transfer fluid 5 associating six solar collectors 1 connected in series.

[0023] FIG. 10 is a perspective view showing the series connection of several solar collectors identical to that of FIG. 1. It will be understood that the ends of two absorption tubes can be connected to each other in any manner known to those skilled in the art. However, the connection between two absorption tubes will preferably be an easy connection to make and easy to undo. The two ends of the absorption tubes can, for example, each end with a nose intended to be able to be force-fitted into a connection tube made of a deformable material. It will be understood that such a connecting tube can be used to connect the ends of the absorption tubes of two solar collectors. To avoid excessive heat loss, the connecting tube is preferably still surrounded by a sleeve made of a material which is both flexible and good thermal insulator, such as foam for example.

It will further be understood that various modifications and / or improvements obvious to a person skilled in the art can be made to the embodiment which is the subject of the present description without departing from the scope of the present invention defined by the appended claims. In particular, the invention is not limited exclusively to a solar thermal collector, but also relates to a photovoltaic solar collector. It will in fact be understood that it is for example possible to replace the tubular device 4 illustrated in FIGS. 4A and 4B by a pipe covered with photovoltaic cells.

We know that the yield of photovoltaic cells decreases with temperature. Under these conditions, instead of using the heat transfer fluid to bring heat to any device, one can use a heat transfer fluid intended to cool the photovoltaic cells. For example, you can pump water into a river and use it as a heat transfer liquid. On the other hand, the function of the glass insulation tube 26 which surrounds the absorption tube 25 is to allow the temperature of the absorption tube to rise as much as possible. It will therefore be understood that, in the case of a photovoltaic solar collector, it is preferable that the tubular device does not include such an insulation tube. Note, however, that certain embodiments of the invention are mixed thermal-solar solar collectors which include an insulation tube.

List of reference numbers:

[0026]

1. Parabolic solar collector;

2. linear parabolic mirror;

3. incident solar rays;

4. tubular device (thermal);

5. heat transfer fluid;

6. circuit for heat transfer fluid;

7. external enclosure;

8. connecting element (wheel)

9. orientation device;

10. flaccid;

11. flaccid;

12. radial bearings;

13. first tube;

14. second transparent tube;

15. vacuum chamber;

16. photovoltaic cells;

17. counterweight;

18. tubular device (photovoltaic);

19. set of photovoltaic cells

20. cradle;

21. metal flanges;

22. aluminum flange:

23. arches;

24. solar rays;

25. absorption tube;

26. glass insulation tube;

27. flange of the insulation tube;

28. compensator;

29. O-ring;

30. aluminum compression flange

Claims (15)

claims 1. Parabolic solar collector (1) comprising a linear parabolic mirror (2) arranged to concentrate the incident solar rays (3) on a tubular device (4; 18) placed at the focal point of the parabola and traversed by a heat transfer fluid (5) , and an external enclosure (7) mechanically resistant and transparent to incident solar rays, characterized in that - the enclosure (7) is a waterproof, rigid and self-supporting enclosure, - the tubular device (4; 18) is fixedly mounted inside the enclosure (7), - the linear parabolic mirror (2) is rotatably mounted on the tubular device (4; 18), - the parabolic mirror (2) is provided with an energetically autonomous orientation device (9) arranged to bear mechanically on a part of the solar collector which is fixed relative to the enclosure (7). 2. Parabolic solar collector according to claim 1, in which the tubular device (4; 18) passes through the enclosure (7) right through, so that the two ends of the tubular device open to the outside, from right through and on the other side of the enclosure. 3. Parabolic solar collector according to claim 1 or 2, wherein the outer enclosure (7) is of circular section and has an axis of symmetry, the tubular device (4; 18) being mounted concentrically with the axis of symmetry. 4. Parabolic solar collector according to claim 3, in which the external enclosure (7) is of substantially cylindrical shape. 5. Parabolic solar collector according to one of claims 3 and 4, wherein the external enclosure (7) comprises at its ends two flanges (10, 11) arranged to serve as a fixed support for the tubular device (4; 18) . 6. Parabolic solar collector according to one of the preceding claims, in which the linear parabolic mirror (2) is movable over 360 ° around the tubular device (4; 18). 7. Parabolic solar collector according to one of the preceding claims, in which the linear parabolic mirror (2) is mounted on the tubular device (4; 18) by means of at least two radial bearings (12) pivoted on the tubular device, each radial bearing comprising a counterweight (17) disposed at one of its ends and being arranged to be fixed to the parabolic mirror by its other end. 8. Parabolic solar collector according to claim 7, in which at least one of the counterweights (17) carries a solar cell associated with the orientation device (9) so as to make the latter energetically autonomous. 9. Parabolic solar collector according to one of the preceding claims, in which the orientation device (9) is fixed to the back of the linear parabolic mirror (2), the orientation device comprising an electric motor powered by a solar cell and a connecting element (8) arranged to bear mechanically on the inner surface of the enclosure (7). 10. Parabolic solar collector according to one of the preceding claims, the parabolic solar collector being a solar thermal collector in which the tubular device (4) comprises a first tube (13) traversed by the heat transfer fluid and a second transparent tube (14) surrounding the first tube and forming an enclosure (15) maintained under vacuum. 11. Parabolic solar collector according to one of claims 1 to 9, the parabolic solar collector being a photovoltaic solar collector in which the tubular device (18) comprises a first tube (13) traversed by a heat transfer fluid, and a set of cells photovoltaic (19) covering the surface of the first tube, the photovoltaic cells being in thermal contact with the first tube. 12. Circuit (6) for heat transfer fluid, the circuit incorporating at least one parabolic solar collector (1) according to one of claims 1 to 10, the solar collector being arranged to supply heat to the heat transfer fluid (5) which travels the tubular device (4). 13. A circuit for heat transfer fluid according to claim 12, wherein the circuit (6) incorporates a set of parabolic solar collectors (1) according to one of claims 1 to 10. 14. A circuit for heat transfer fluid according to claim 13, wherein the tubular devices (4) of the various sensors (1) are connected in series. 15. Installation for production and / or storage of thermal energy comprising a circuit (6) for heat transfer fluid according to one of claims 12 to 14.