EP2449319A2

EP2449319A2 - Adjustable solar collector

Info

Publication number: EP2449319A2
Application number: EP10742022A
Authority: EP
Inventors: Sylvianne Delaby; Yves Didier Gotteland; Christian Grialou; Céline GRYCZKA épouse ERIPRET; Jean-Paul Longuemard; Christophe Trinquart
Original assignee: Therpho (Thermique Photonique)
Current assignee: Therpho (Thermique Photonique)
Priority date: 2009-07-02
Filing date: 2010-07-01
Publication date: 2012-05-09
Also published as: CN102575876A; WO2011001118A2; FR2947619A1; WO2011001118A3; FR2947619B1

Abstract

The invention relates to a solar collector (1) including a frame (2), a reflector (7) having a parabolic cross-section, and a tube (8) for the circulation of a coolant, said tube being provided along the focal axis (A) of said reflector. The reflector is rotatably movable relative to the frame, about said focal axis. The tube is transparent and has an inner diameter of at least 15 m.

Description

ORIENTABLE SOLAR SENSOR

Technical field of the invention

The present invention relates to a solar collector. In particular, the present invention relates to a solar collector in which circulates a specific heat transfer fluid.

State of the art

There are concentrating solar collectors, in which the sun's rays are reflected by a reflector on an absorber. This allows the use of a smaller absorber than the total sensor size, which reduces heat loss and increases sensor efficiency.

In a known type of solar collector, the reflector used is a reflector of parabolic section or arcuate, and extending in a longitudinal direction. A coolant circulates in a tube centered on the focal axis of the reflector.

Generally, a solar pointer system rotates a subassembly including the reflector and the tube, depending on the orientation of the sun. This type of solar collector has several disadvantages. Indeed, the subassembly to rotate has a large mass, which implies a high torque and therefore the use of a relatively powerful engine. In addition, existing sensors of this type are sized for industrial applications and are not suitable for domestic applications such as domestic water heating.

In rare cases, all components of the solar collector are fixed. The efficiency of this type of sensor is limited because the reflector is not always in the right orientation relative to the sun.

Summary of the invention

A problem that the present invention proposes to solve is to provide a solar collector which does not have at least some of the aforementioned drawbacks of the prior art. In particular, an object of the invention is to provide a sensor which may be suitable for a domestic application and which has a good performance. Another object of the invention is to provide a solar sensor that does not require a high power engine. The solution proposed by one embodiment of the invention is a solar collector comprising a frame, a parabolic section reflector and extending parallel to a focal axis, and a tube capable of being connected to flexible pipes at both ends thereof. for the circulation of a coolant through said tube, said tube being arranged along the focal axis of said reflector. The reflector is rotatable relative to the frame, about said focal axis, and the focal axis passes within a curve comprising said parabolic section and a line segment connecting the ends of said parabolic section. The tube is made of transparent material and has an internal diameter of at least 15 mm.

The rotation of the reflector makes it possible to follow the variation of the orientation of the sun during the day, and thus to improve the efficiency of the solar collector. Thanks to this good performance, it is possible to size the solar collector to suit a domestic application, without being too bulky. As the tube is arranged along the focal axis and the reflector rotates about the focal axis, the tube can remain fixed during the rotation of the reflector. Thus, it is not necessary to use a powerful motor. In addition, the position of the focal axis inside the parabola allows a good distribution of the weight of the reflector around its center of rotation. This helps to reduce the power required.

Preferably, the frame comprises a fixed part intended to be placed on a support surface, and a movable part, said movable part being able to pivot relative to said fixed part about a horizontal axis, said tube being fixed relative to said movable portion, said reflector being connected to said movable portion rotatably.

The support surface is for example the floor, a horizontal roof or an inclined roof.

Advantageously, said focal axis is orthogonal to said horizontal axis.

Thanks to these features, the moving part can be positioned according to the longitude and the season to orient the focal axis approximately perpendicular to the sun's rays. However, high accuracy is not necessary to maintain acceptable solar collector efficiency. Thus, the moving part can for example be moved periodically, for example quarterly, manually. Alternatively, an electric motor can be provided to position the movable portion relative to the fixed portion under the control of a programmed control unit. For example, the control unit automatically adjusts this position around the horizontal axis from a location longitude data and an internal clock.

Advantageously, said tube has an internal diameter of at least 15 mm. Preferably, said internal diameter is at least 35 mm.

In this case, it is possible to admit a difference of a few degrees between the effective orientation of the reflector around the focal axis and its optimal orientation. It is therefore not necessary to use a motor and a control device to achieve a continuous and accurate rotation.

According to one embodiment, the solar collector comprises a motor adapted to rotate said reflector about said focal axis.

Advantageously, said motor is fixed to said movable part, said motor being able to rotate said reflector with respect to said movable part.

Preferably, the solar collector comprises a control device adapted to control the motor to rotate the reflector. The control device can for example rotate the motor gradually during the day, depending on the time, and reposition the reflector in an initial orientation at the end of the day.

According to one embodiment, the solar sensor comprises a brightness sensor, said control device being able to control the motor based on a signal from said brightness sensor.

The brightness sensor allows a fine adjustment of the orientation of the reflector, from a direction determined according to the time.

According to one embodiment, the solar collector comprises at least one temperature sensor capable of measuring the temperature of a fluid flowing in said tube.

The signal from the temperature sensor may be used by the controller to control a pump for circulating the fluid and / or the motor. This allows, among other things, to avoid overheating.

Brief description of the figures The invention will be better understood, and other objects, details, features and advantages thereof will appear more clearly in the following description of a particular embodiment of the invention, given solely for illustrative purposes and not limiting, with reference to the accompanying drawings. On these drawings:

FIG. 1 is a perspective view of a solar collector according to one embodiment of the invention,

FIG. 2 is a sectional view of the reflector of the solar collector of FIG.

Detailed description of an embodiment of the invention

The solar collector 1 comprises a frame 2, a reflector 7 and a tube 8. It is intended to heat a coolant circulating in the tube 8. The solar collector 1 is for example placed at the bottom of the garden of a dwelling and does not require therefore no modification of the roof. It is connected to the water heater of the house. Thus, the heated heat transfer fluid can in turn heat domestic water in the domestic water heater. Of course, the solar collector 1 may be suitable for other applications.

The frame 2 has a fixed part and a movable part.

The fixed part is intended to rest on a flat surface, for example the ground, a horizontal roof or an inclined roof. In the example shown, the fixed part comprises four feet 3 carrying a frame 4 of rectangular shape, and two arches 5 fixed to the frame 4. Alternatively, the shape of the fixed part may be adaptable to the situation, for example to the tilting of the roof.

The movable part comprises a frame 6 of rectangular shape. As shown in FIG. 1, the small lower side of the frame 6 is connected to a short side of the frame 4, and the small upper side of the frame 6 is connected to the arches 5. The frame 6 can pivot relative to the fixed part of the frame frame 2 about a horizontal axis B, the small upper side of the frame 6 sliding relative to the arches 5. A locking mechanism (not shown) makes it possible to fix the frame 6 in a desired position.

The reflector 7 is connected to the frame 6. It has a concave reflecting wall 9 extending parallel to an axis A, and two end walls 10. The axis A is orthogonal to the axis B. As shown in Figure 2, the wall 9 has a parabolic section. In addition, it can be seen in this figure that the focus of the dish is located at a height less than the height of its ends 15. In other words, the focus is located inside the parabola. The aforementioned axis A passes through the focus of the parabola and is therefore the focal axis A of the wall 9. The axis A therefore passes inside a curve comprising the parabola and a line segment 16 connecting the ends 15 the parable.

The tube 8 is fixed relative to the frame 6. It extends along the axis A. A pump and two hoses (not shown) are connected at its ends to circulate the coolant.

The reflector 7 is rotatable relative to the frame 6. More precisely, the reflector 7 can rotate about the axis A by means of two bearings (not shown) connecting the end walls 10 to the frame 6, at the level of the axis A.

The solar collector 1 also comprises a motor (not shown) fixed to a support plate 11 integral with the frame 6. The motor makes it possible to turn the reflector 7 with respect to the frame 6. A control device (not shown) is connected to the motor and pump and allows the solar collector to operate 1.

In one embodiment, the solar collector 1 may also comprise a brightness sensor and / or two temperature sensors able to measure the temperature of the fluid at the inlet and at the outlet of the tube 8.

Since, in operation, the tube 8 can reach a high temperature, it is possible to provide a transparent protection tube, which surrounds the tube 8 at a distance. Alternatively, there may be a transparent plate on the open face of the reflector 7, for example polycarbonate. Thus, it limits the risk of contact with the tube 8.

The operation of the solar collector 1 is as follows.

The solar collector 1 is placed in a place exposed to the sun, for example at the bottom of a garden or on a roof. If the reflector 7 is oriented correctly, the sun's rays are reflected towards the tube 8, in which an energy conversion takes place which heats the coolant circulating in the tube 8.

This is illustrated in Figure 2 which shows the section of the wall 9. This section has the shape of a parabola. The tube 8 passes through the focus of the dish.

In FIG. 2, an incident ray 12 is reflected by the wall 9 at the point 13. The reflected ray 14 is directed towards the tube 8 because the incident ray 12 is parallel to the y axis.

Figure 2 represents an optimal situation. In practice, depending on the orientation of the reflector 7 with respect to the sun, the incident rays are not necessarily parallel to the y axis. However, the solar collector 1 allows a rotation of the solar collector 7 around the axis A and around the axis B, to be closer to this optimal situation.

The angular position of the reflector 7, around the axis B, has a relatively limited influence on the efficiency of the solar collector 1. Ideally, the axis A should be perpendicular to the sun's rays. In practice, a deviation of 15 ° can be allowed without an unacceptable decrease in yield. Thus, it is not necessary to change the inclination of the frame 6 during the daily operation of the solar collector 1. For example, this inclination is adjusted during the installation of the solar collector 1, depending on the longitude where is installed the solar collector 1. Then, this inclination can be changed periodically, for example every three months, to take into account the variation of the height of the sun according to the seasons. For this, an operator slides the small upper side of the frame 6 relative to the arches 5, before setting it in a new position. The locking mechanism makes it possible, for example, to fix the frame 6 according to three determined inclinations corresponding respectively to an orientation of the axis A at 30 °, 45 ° and 60 ° with respect to the horizontal. Alternatively, the locking mechanism or an electric motor allows continuous adjustment.

The angular position of the reflector 7, around the axis A, has a greater influence on the efficiency of the solar collector 1. As can be deduced from FIG. 2, an incorrect orientation causes the reflected ray 14 to pass through. next to the fireplace. One can admit a certain deviation while maintaining an acceptable yield, because the tube 8 has a non-zero diameter and thus intercepts the rays passing near the home. The permissible deviation depends in particular on the internal diameter of the tube 8. It may be, for example, 3.25 °, in a particular case of sizing of the solar collector 1. Since the azimuthal orientation of the sun varies by 15 ° per hour, it appears important to rotate the reflector 7 about the axis A to follow the orientation of the sun during the day. For this, the aforementioned control device controls the motor to rotate the reflector 7 progressively, depending on the time. At the end of the day, the reflector 7 is returned to the initial position for the next day. Theoretically, the motor should rotate the reflector 7 continuously, 15 ° per hour. However, since it is possible to admit a difference of some degree between the effective orientation and the optimal orientation of the reflector 7, the motor can be controlled to rotate the reflector a few degrees periodically, for example 3.75 ° every quarter time.

In one embodiment, the controller uses the signal from the brightness sensor to fine tune around the predetermined position as a function of time.

In one embodiment, the control device controls the pump to change the flow rate of the heat transfer fluid in the tube 8, depending on the inlet and / or outlet temperature. This allows to adapt the flow to the sun and to avoid overheating. For the same purpose, in case of excessive temperature, the control device can control the motor to rotate the reflector 7 so as to protect it from the sun.

Since the reflector 7 must pivot and the tube 8 is fixed relative to the frame 6, the mass to be rotated is not high. A high engine torque is not necessary and the engine can be a low power engine. For example, the motor may be an electric motor powered by 24 V DC, low power (for example 12 W), associated with a gearbox.

Thanks to the possibility of double orientation of the reflector 7, the solar collector

1 has a good performance without being very bulky. For example, the frame 2 can occupy a floor area of up to 2 m ² , and the solar collector 1 can provide enough heat to meet the hot water needs of a single-family dwelling. The solar collector 1 can therefore be sized for a domestic application.

According to an example of dimensioning, the frame 2 is made of aluminum and the frame 4 has a dimension of 0.6 m × 1.5 m. The reflector 7 has a length of

2 m. The tube 8 is made of transparent material and has a length of 2 m. The allowable difference between the effective orientation of the reflector 7 and the optimum orientation around the axis A ₅ without unacceptable drop in efficiency, has been determined with such a dimensioning For an internal diameter of the tube 8 of 26 mm, 36 mm or 46 mm, the permissible deviation is respectively 0.2 °, 3.25 ° and 4.5 °. The tube 8 therefore preferably has an internal diameter of at least 35 mm. Such a diameter has the further advantage of avoiding turbulence in the coolant.

In operation, the transparent tube 8 contains a heat transfer fluid capable of heating up in volume by absorption of solar radiation. Many absorbent fluids may be suitable for this purpose. Preferably, the fluid is chosen in a manner adapted to the size of the tube to be able to absorb substantially all the power of the solar radiation reflected on the tube by the reflector 7. For this, the product of the diameter of the tube 8 by the energy absorbency of the fluid in the spectrum of solar radiation must be sufficiently high. Conversely, this product should not be too high for the heating of the fluid can be relatively homogeneous throughout the section of the tube. A suitable selection criterion is to obtain a product of between 1 and 10, preferably close to 3.

Thus, for a tube of diameter greater than or equal to 35 mm, the selected fluid preferably has an average energy absorbency in the spectrum of solar radiation greater than or equal to 0.5 cm ^-1 .

To avoid turbulence, the velocity of the flow in the tube 8 must not exceed a certain threshold. For example, for a tube of internal diameter equal to 35 mm, a satisfactory speed range is between 0 and about 0.4 ms ^-1 This corresponds to a volume flow rate of between approximately 0 and 1500 l / h.

For a given level of sunshine, there is a relation between the volume flow rate of fluid in the tube 8, the length of the tube 8, and heating of the fluid in the solar collector 1. For the dimensioning of the tube 8 and the reflector 7, a length of less than 4m may be preferred to limit the wind extent of the sensor

1. A length of 2m has proved satisfactory for a domestic installation intended for the production of domestic hot water. In such an application, if the hot water tank must be maintained at, for example, 80 ^° C., it has been found that the temperature of the fluid at the outlet of the solar collector must be a few degrees higher than this setpoint, for example between 85 ° C. C and 90 ⁰ C given the losses may exist in the coolant circuit between the solar collector and the hot water tank. Indeed, the hot water tank can be typically a distance of a few tens of meters. When the coolant is aqueous, a temperature below 100 ⁰ C is preferably maintained to maintain a fully liquid phase.

For the realization of the transparent tube 8, relevant criteria are mechanical strength, transparency to solar radiation, thermal insulation by conduction and thermal expansion. In this respect, the choice of borosilicate glass is advantageous. In particular, this glass has a high transparency in the near infrared. For the mechanical strength of a borosilicate tube with a length of 2 m, a wall thickness of 1.5 mm to 2.5 mm can be chosen.

Other transparent materials may be envisaged for the tube 8, for example the polycarbonates. However, this material has a high thermal expansion, for example 5 times larger than an aluminum frame, which requires to provide compensation devices.

A heat transfer fluid that can be used in the transparent tube 8 is a suspension of diffusing particles in a moderately absorbent liquid. Such a fluid is described in application PCT / FR2010 / 051293 filed June 24, 2010 which is incorporated herein by reference.

The aforementioned control device can be realized in different forms, unitarily or distributed, by means of hardware and / or software components. Useful hardware components are ASIC specific integrated circuits, FPGA programmable logic networks or microprocessors. Functions of this control device can in particular be:

- Tilt adjustment (site) of the frame 6 of the frame relative to the ground, according to an internal clock,

- Position adjustment (azimuth) of the reflector 7 according to an internal clock,

Active safety in the event of overheating of the coolant, - Automatic start and stop of the coolant circulation pump according to the difference between the temperature in the tube 8 and a setpoint. The use of the verb "to include", "to understand" or "to include" and its conjugated forms does not exclude the presence of other elements or steps other than those set out in a claim. The use of the indefinite article "a" or "an" for an element or a step does not exclude, unless otherwise stated, the presence of a plurality of such elements or steps.

In the claims, any reference sign in parentheses can not be interpreted as a limitation of the claim.

Although the invention has been described in connection with a particular embodiment, it is obvious that it is not limited thereto and that it comprises all the technical equivalents of the means described and their combinations if they are within the scope of the invention.

Claims

1. Solar collector (1) comprising a frame (2), a reflector (7) of parabolic section and extending parallel to a focal axis (A), and a tube (8) adapted to be connected to two flexible hoses. both ends for circulating a coolant through said tube, said tube being arranged along the focal axis (A) of said reflector, wherein said reflector is rotatable relative to the frame, about said focal axis, and said focal axis passes inside a curve comprising said parabolic section and a line segment connecting the ends (15) of said parabolic section, characterized in that said tube is made of transparent material and has an internal diameter of at least 15 mm.

Solar collector according to claim 1, wherein the tube has an internal diameter of at least 35 mm.

3. Solar collector according to claim 1 or 2, wherein the tube has a length less than 4 m.

4. Solar collector according to one of claims 1 to 3, wherein the transparent material is boro silicate.

5. Solar collector according to one of claims 1 to 4, wherein the tube has a circular inner section.

6. Solar collector according to one of claims 1 to 5, wherein the frame comprises a fixed part intended to be placed on a support surface, and a movable part (6), said movable part being able to pivot relative to said part fixed around a horizontal axis (B), said tube being fixed with respect to said movable part, said reflector being connected to said movable part in a rotational manner.

The solar sensor of claim 6, wherein said focal axis is orthogonal to said horizontal axis.

8. solar collector according to claim 6 or 7, comprising a motor adapted to rotate said reflector about said focal axis.

9. Solar collector according to claim 8, wherein said motor is fixed to said movable part, said motor being able to rotate said reflector relative to said movable part.

10. A solar sensor according to claim 8 or 9, comprising a control device adapted to control the motor to rotate the reflector during the day and reposition the reflector in an initial orientation at the end of the day.

11. The solar sensor as claimed in claim 10, comprising a brightness sensor, said control device being able to control the motor based on a signal from said brightness sensor.

12. Solar collector according to one of claims 1 to 11, comprising at least one temperature sensor capable of measuring the temperature of a fluid flowing in said tube.

13. Solar collector according to one of claims 1 to 12, comprising a transparent protective plate which covers said tube (8).

A method for producing a hot fluid with a solar collector according to one of claims 1 to 13, comprising:

expose the solar collector (1) to sunlight,

circulating in the tube (8) a heat transfer fluid having an energy absorptivity greater than 1 cm ^-1 for sunlight.

15. The method of claim 14, wherein the coolant is heated to a temperature below 100 ⁰ C.

16. The method of claim 14 or 15, wherein the coolant flows in the tube (8) at a speed less than 0.5 ms ^-1 .