WO2017103410A1

WO2017103410A1 - System for the optimised monitoring of a light source

Info

Publication number: WO2017103410A1
Application number: PCT/FR2016/053339
Authority: WO
Inventors: Sébastien QUENARD; Philippe Coronel; Gabriel DELEPIERRE; Gilbert PITONE
Original assignee: Commissariat à l'énergie atomique et aux énergies alternatives; Delta Concept
Priority date: 2015-12-14
Filing date: 2016-12-12
Publication date: 2017-06-22
Also published as: FR3045243A1; FR3045243B1; EP3391534A1

Abstract

The invention relates to a system for monitoring a source of light energy (1), comprising: a pivotably mounted solar receiver (2); a thermomechanical transducer (3, 4) comprising first (3) and second (4) thermal actuators each having a thermostatic bimetallic element deformed according to the solar radiation that they receive; a first light filtering body (33) over the first actuator (3); a second light filtering body (43) over the second actuator (4); a driving body (31, 41) having a sliding direction; and a mechanical transmission (5) transforming the sliding of the driving body (31, 41) into pivoting of said solar receiver, and comprising a third thermal actuator with a thermostatic bimetallic element deformed according to the ambient temperature and isolated from the solar radiation, the deformation thereof modifying the transmission ratio between the sliding course of the driving body and the pivoting angle of said solar receiver (2).

Description

SYSTEM FOR OPTIMIZED MONITORING OF LIGHT SOURCE

The invention relates to the optimized tracking of a light source, and in particular receivers or solar panels whose orientation changes depending on the position of the sun.

Solar panels recover energy in different forms: photovoltaic panels convert solar energy into electrical energy and thermal panels convert solar energy into heat in a heat transfer fluid.

Because of the relatively low levels of recovered power, it is particularly important to optimize the recovery of solar energy by such solar panels. Thus, technical developments have been made to change the orientation of solar panels according to the position of the sun. By modifying the angle of incidence of the sun on a solar panel, one can thus optimize continuously the quantity of energy recovered, at different times of the day or at different seasons.

The document WO2010 / 127262 describes a system for orienting the angular position of a pivoting solar panel. The angular position of the solar panel is controlled autonomously by two thermal actuators soliciting the solar panel in opposite manner. The thermal actuators are subjected to distinct radiation by the sun, due to the movement of a movable shutter. Each thermal actuator is here formed of a bimetallic thermostatic bimetallic. For a given solar radiation, the thermal actuators undergo a different heating leading to a pivoting of the solar panel to a position of equilibrium, for which the solar illumination is optimal.

Such a system has disadvantages. Such a system is unsuitable for modulating the amplitude of pivoting of the solar panel according to the season. Such a system is, for example, excessively sensitive to the temperature variation of the external environment. In addition, the system has dimensions quite difficult to industrialize.

JP H1 1 354824 discloses a tracking system of a source of light energy. This system comprises a solar receiver pivotally mounted relative to an axis, a thermomechanical transducer provided with first and second thermal actuators each having a thermostatic bimetallic deformed according to the solar radiation they receive. Luminous filtering elements surmount the thermal actuators.

The invention aims to solve one or more of these disadvantages. The invention thus relates to a system for monitoring a source of energy light as defined in claim 1. The invention also relates to the variants defined in the dependent claims. It will be understood by those skilled in the art that each of the features of the variants of the dependent claims may be independently combined with the features of claim 1, without necessarily constituting an intermediate generalization.

Other characteristics and advantages of the invention will emerge clearly from the description which is given hereinafter, by way of indication and in no way limitative, with reference to the appended drawings, in which:

FIG 1 is a schematic side view of a solar panel system orientable autonomously, according to an exemplary implementation of the invention.

FIG 2 is a schematic sectional view of a first variant of autonomous actuator for the implementation of the invention;

FIG 3 schematically illustrates fins of a light filtering device and its operating parameters;

FIG. 4 illustrates a schematic sectional view of a bimetallic strip for an autonomous actuator;

FIG 5 is a schematic sectional view of a second variant of autonomous actuator for the implementation of the invention;

FIG. 6 is a diagrammatic sectional view of a first variant of an exemplary thermal actuator for a mechanical transmission of the system;

FIG. 7 is a diagrammatic sectional view of a second variant of thermal actuator for a mechanical transmission of the system;

FIGS. 8 and 9 illustrate two different positions of a transmission member of the mechanical transmission. The invention proposes to drive a solar energy receiver (for example a solar panel) pivotally about an axis, by means of two thermal actuators receiving solar radiation with distinct sensitivities, soliciting the solar energy receiver in opposite directions. The sliding of these thermal actuators is converted into pivoting of the solar receiver by a mechanical transmission. Another thermal actuator modifies the transmission ratio between the sliding stroke of the thermal actuators and the pivoting stroke of the solar receiver.

Figure 1 is a schematic side view of a solar energy recovery system 1 according to an exemplary embodiment. The solar energy recovery system 1 comprises a solar panel 2, thermal actuators 3 and 4, and a mechanical transmission 5. The structure of the system 1 is described for illustrative purposes but may of course be implemented differently in the context of the invention. The solar panel 2 is here a photovoltaic panel but the invention also applies to any other type of solar panel, for example a solar thermal panel or a reflector of a solar concentrator.

The solar panel 2 here comprises a group of photovoltaic cells 21 and a frame or frame 22. The photovoltaic cells 21 are fixed to the frame 22. The solar panel 2 further comprises a vertical base 23 embedded in the ground 25. The assembly frame 22 / photovoltaic cells 21 is pivotally mounted about an axis 24. The angle of incidence of the sun on the photovoltaic cells 21 can thus be modified as a function of the pivoting of the frame 22 about the axis 24.

The energy recovery system 1 comprises a thermomechanical transducer, including thermal actuators 3 and 4 biasing the solar panel 2 in opposite directions of rotation about the axis 24, by means of respective drive members 31. and 41 (the driving members 31 and 41 being secured to form the same drive member). The drive members 31 and 41 are slidably driven (along a horizontal axis in the example) and are coupled to a mechanical transmission 5. The mechanical transmission 5 is fixed to the frame 22 and converts the sliding of the drive members 31 and 41 as pivoted solar panel 2 about the axis 24. As detailed below, the thermal actuators 3 and 4 each comprise at least one thermostatic bimetallic deformed depending on the solar radiation received. The thermal actuators 3 and 4 are respectively surmounted by luminous filtering members 33 and 43. The luminous filtering members 33 and 43 are intended to have a respective optimum incidence direction, for which the transmitted light power is maximum. The light power transmitted by each filter element decreases, when the incidence of solar radiation is inclined relative to its optimal direction of incidence. The respective optimum bearing directions of the thermal actuators 3 and 4 are different. An example of a light filtering member is detailed below.

Figure 2 is a schematic sectional view of a first variant of thermal actuator 4 for the implementation of the invention. The thermal actuator 4 here comprises a rod forming the drive member 41. The thermal actuator 4 comprises a support fixed to the ground 25. The rod 41 is slidably mounted relative to the support in a horizontal direction. The support here comprises a side wall 421, and lids 423 and 425. The support advantageously delimits a closed cavity 422 via the side wall 421 (for example of circular or rectangular section) and lids 423 and 425. side wall 421 typically has a cylindrical shape, with a generatrix parallel to the sliding direction of the rod 41. In particular, the rod 41 is slidably mounted via a guide surface 424 of the cover 423. An overlay of thermostatic bimetals 413 is housed inside the cavity 422. The sliding guide of the rod 41 can The movements of the rod 41 are applied to the mechanical transmission 5. The thermal actuator 4 is positioned to receive the solar radiation selectively as a function of the angle of rotation. incidence of this solar radiation. The light filtering member 43 is thus interposed between the solar radiation and the thermal actuator 4. The light filtering member 43 is here formed of a succession of opaque or reflecting lamellae 431, inclined with respect to the horizontal and vertically. The strips are here fixed on the upper surface of the side wall 421. Spaces are formed between the lamellae 431 to allow the light to reach the cavity 422 according to certain incidences. The inclination of the lamellae 431 makes it possible to define the optimum direction of incidence of the luminous filtering member 43.

FIG. 3 illustrates an example of lamella geometry 431 making it possible to give an example of a proportion of solar radiation that can reach the thermal actuator 4. With the inclination of the fins 431 with respect to the vertical, Θ the angle of incidence solar radiation with respect to the vertical, the pitch between the fins 431, the width Y of the side surface 421 illuminated between two fins may be defined as follows:

Y = a * tan (Θ) / tan (a)

For Θ in the interval [0, a], the proportion T of radiation reaching the transparent cavity can be defined as

T = tan (Θ) / tan (a) For a solar radiation of power E applied with the incidence Θ, the solar power reaching the side wall 421 can approximately be defined by the relation:

P = E * tan (Θ) / tan (a)

The lamellae 431 may advantageously have a reflective back surface and an absorbent front surface to maximize the effect of solar radiation. The lamellae 431 may for example have an inclination of between 20 and 70 °, typically an inclination of 45 °. The lamellae 431 may have a flat shape. The lamellae 431 may be arranged to ensure that an incident ray at Θ = 0 ° does not reach the side wall 421. The number of lamellae 431 makes it possible to determine the accuracy of the system with respect to the solar radiation. The lamellae 431 may be fixed by any appropriate means (screw, glue, weld) on the side wall 421, or on another support remote from the wall 421, in order to provide a space between these lamellae 431 and the side wall 421.

The bimetallic strips 413 are deformed as a function of the radiation received by the support. A temperature variation of the bimetallic strips 413 leads to a variation in their bulk in the direction of sliding of the rod 41. The bimetals 413 are configured to drive the rod 41 in sliding, for example during an increase in their temperature.

The rod 41 is here secured to a stop ring 412. An overlap of bimetals 413 has one end in contact with the ring 412 and another end in contact with the bottom cover 425. Thus, during a thermal expansion of the bimetallic stack 413, the assembly formed of the ring 412 and the rod 41 is moved (or exerts a directed force) to the right in the configuration illustrated in FIG.

In the configuration illustrated in FIG. 2, the thermal actuator thus comprises a superimposition of bimetallic strips 413. In the illustrated configuration, the bimetallic bimetals 413 each form a concave plate at a temperature of 20 ° C. The concavities of FIG. at least two superposed bimetals 413 have opposite orientations. Thus, with such a superposition of successive bimetallic strips, the concavities of which have opposite orientations, it is possible to multiply the amplitude of the sliding of the rod 41 for a given heating. It is also conceivable to superimpose several successive bimetallic strips 413 with concavities having the same orientations, in order to increase the force applied by these bimetallic strips on the ring 412 and the rod 41.

Two successive bimetallic strips 413 of the stack can be fixed together by their periphery, or simply be pressed together against each other. their periphery due to the return force exerted by the rod 31 of the thermal actuator 3 disposed in symmetry, or because of a possible unillustrated return spring.

The bimetals 413 may for example have a shape (in projection in the sliding direction of the rod 41) circular, rectangular or square.

The bimetallic strips 413 chosen are advantageously of the type with progressive deformation over the target operating temperature range, in order to be able to carry out a progressive drive of the solar panel 2.

The use of a closed cavity 422 aims to maximize the heating of the thermostatic bimetals 413 for a given solar radiation power. The closed cavity 422 makes it possible to create a greenhouse effect by radiative forcing. Such a greenhouse effect maximizes the heating of bimetallic strips 413 regardless of the orientation of the sun.

Advantageously, the side wall 421 is transparent to the solar radiation and typically allows more than 50% of the incident solar radiation to pass to the cavity 422. The side wall 421 may for example be made of different transparent materials such as glass, polycarbonate, methacrylate, or plexiglass.

Advantageously, the inner or outer face of the side wall 421 comprises a reflective coating, intended to reflect the incident light radiation from the inside of the cavity 422, but intended to let the light radiation from outside pass through, in order to maximize the thermal energy that can be transferred to bimetallic strips 413.

Advantageously, an outer face or an inner face of the side wall 421 comprises a coating absorbing solar radiation to convert it into thermal energy.

To maximize the thermal insulation of the cavity 422 with respect to the temperature of the ambient environment, it is conceivable to form a side wall 421 having a combination of two or more transparent insulated walls separated by gas or vacuum.

Identical properties and structures can be used for lids cooperating with the side wall 421 to delimit a closed cavity 422.

Advantageously, the cavity 422 is filled with gas (for example air or argon) or is placed under vacuum, in order to limit the heat exchange between the cavity 422 and the outside. The cavity 422 may be hermetic with respect to the outside, or on the contrary present openings if it is desired on the contrary to reduce the temperature gradient applied on the bimetals 413 for a given solar radiation. The thermal actuator 3 has the same structure as the thermal actuator 4 but is arranged symmetrically with the thermal actuator 4. As detailed previously, the light filtering member 33 of the thermal figure 3 has an optimal direction of incidence. different from that of the luminous filtering member 43. The difference in the optimal incidence directions is for example obtained by using lamellae having different orientations for the luminous filtering members 33 and 43.

The use of another thermal actuator 3 exerting in the opposite direction reduces the sensitivity of the system 1 to the ambient temperature. Indeed, the effect of the ambient temperature on a thermal actuator will be compensated by the effect of this same ambient temperature on the other thermal actuator.

Figure 4 is a schematic sectional view of an example of bimetallic 413 can be included in a thermal actuator 4 of a system 1 according to the invention.

A bimetal usually comprises two layers of different metals, flexible, welded or glued or riveted by any suitable means against each other. These two metal layers are frequently cold rolling welded. Commonly used bimetals include invar and nickel having different expansion coefficients. Since the thermal expansion of the two layers is different, the bimetallic strip deforms with temperature variations.

In the illustrated example, the bimetallic strip 413 thus comprises a first layer 415 integral with a second layer 414. The material of the first layer 415 here has a coefficient of thermal expansion less than that of the layer 414. The layer 414, presenting the highest coefficient of thermal expansion, advantageously comprises a coating 418 (for example in the form of paint, surface texturing, or deposition) intended to promote the light absorption and therefore the heating of the layer 414. bimetallic bames, such as that sold under the reference 108 SP provided for example by the company IMPHY, can for example be used. The bimetallic strip 413 here forms a concave shaped plate at a temperature of 20 ° C.

A through bore 416 is formed in the middle part of the bimetal 413, through the layers 414 and 415 and through the coating 418. The bore 416 allows the passage of the rod 41 to allow its sliding. By elsewhere, the edges of the bores 416 can be used to ensure sliding guidance of the rod 41.

Figure 5 is a schematic sectional view of a second variant of thermal actuator 4 for the implementation of the invention. The thermal actuator 4 also comprises a support fixed to the ground 25, a rod forming the drive member 41 and slidably mounted relative to the support. The support here comprises a side wall 421, and covers 423 and 425, delimiting a closed cavity 422. An overlay of thermostatic bimetals 413 is housed inside the cavity 422. The movements of the rod 41 are applied to the transmission mechanical 5.

A light filtering member 43 is interposed between the solar radiation and the thermal actuator 4. The light filtering member 43 is formed of a succession of opaque or reflecting lamellae 431, inclined relative to the horizontal and the vertical and fixed on the upper surface of the side wall 421. Spaces are formed between the lamellae 431 to allow the light to reach the cavity 422 according to certain incidences. The inclination of the lamellae 431 makes it possible to define the optimum direction of incidence of the luminous filtering member 43.

The bimetallic strips 413 are deformed as a function of the radiation received by the support. A temperature variation of the bimetallic strips 413 leads to a variation in their bulk in the direction of sliding of the rod 41. The bimetals 413 are configured to drive the rod 41 in sliding, for example when their temperature drops.

The rod 41 is here secured to a stop ring 412. An overlap of bimetallic strips 413 has one end in contact with the ring 412 and another end in contact with the cover 423. Thus, during a thermal expansion of the stack bimetallic 413, the assembly formed of the ring 412 and the rod 41 is moved (or exerts a directed effort) to the left in the configuration shown in Figure 5. The bimetallic strips 413 of the second variant can be identical to those described with reference to the first variant of the thermal actuator 4.

The thermal actuator 4 may have the following thermal balance:

P = K. S. ΔΤ

With P the received luminous power, S the heat exchange surface, K the thermal exchange coefficient of the thermal actuator 4 with the outside, and ΔΤ the temperature increase of the thermal actuator 4 for this luminous power. . Assuming that one can model the bimetallic strips 413 by a linear model, and in the absence of compensating thermal actuator 3, one can define the following relation for the thermal actuator 4:

X41 = A. ΔΤ

With X41 the displacement of the rod 41 and A a thermomechanical transformation coefficient of the combination of bimetals 413 (A will be defined for example according to the dimensions, materials and the number of bimetallic strips 413). We can then define the following relation:

X41 = A. P / (K S)

The linearity of the thermal actuator 4 is favored by the presence of a closed cavity 422 and also depends on the choice of material for the bimetallic strips 413. The linearity of the thermal actuator 4 can also be favored by the bimetallic production parameters. 413.

Simulations have been carried out with different configurations of thermal actuator 4. Simulations have in particular been carried out with bimetals of circular shape in projection, having a concavity at a temperature of 20 ° C, formed from a composition of 108SP, and subjected to a temperature variation of 75 ° C.

For a diameter of bimetallic strips of 15 mm, with a stack of bimetals with opposite concavities with a height of 60 mm, a sliding stroke of 7.2 mm is obtained with a stiffness of 4.7 N / mm.

For a diameter of bimetallic strips of 30 mm, with a stack of bimetallic strips with opposite concavities with a height of 100 mm, a sliding stroke of 10 mm with a stiffness of 27.6 N / mm is obtained.

Thus, one skilled in the art can easily determine the choice of bimetallic dimensions 413 for the thermal actuator 4 as a function of the desired sliding stroke and the forces to be exerted.

FIG. 6 is a schematic sectional view of a first variant of mechanical transmission 5. As previously detailed, the mechanical transmission 5 has a function of transforming the sliding of the driving member formed of the rods 31 and 41, pivotally solar panel 2 about the axis 24 (here represented in the form of a tree). The mechanical transmission 5 also has a function of modifying the transmission ratio between the sliding stroke of the rods 31 and 41, and the pivot angle of the solar panel 2, as a function of the ambient temperature. For this purpose, the mechanical transmission 5 comprises a thermal actuator 6 with thermostatic bimetals 613. The thermal actuator 6 comprises a support 62. One end of each of the rods 31 and 41 is embedded in the support 62, in order to drive the thermal actuator 6 in horizontal sliding. The thermal actuator 6 here comprises a rod 51, sliding vertically relative to the support 62. The position of the rod 51 defines the transmission ratio of the mechanical transmission 5, as detailed below. The support 62 here comprises a side wall 621, and covers 623 and 625. The support 62 advantageously delimits an open cavity 622, unillustrated orifices that can be arranged in the side wall 621 and / or in the covers 623 and 625. cavity 622 is intended to communicate with the outside so that its temperature is representative of that of the ambient air. The side wall 621 and / or the covers 623 and 625 are opaque (and advantageously reflective) in order to mask the bimetals 613 with respect to the solar radiation, to limit the power of the solar radiation in the cavity 622, and thus to limit the heating of the bimetallic strips. 613 induced by this solar radiation.

The rod 51 can be slidably mounted via a cover guide 623. An overlay of thermostatic bimetals 613 is housed inside the cavity 622. The thermostatic bimetals 613 may have a structure similar to that of the thermostatic bimetals 413 previously detailed.

The bimetallic strips 613 are deformed as a function of the ambient temperature in the cavity 622. A temperature variation of the bimetallic strips 613 leads to a variation in their bulk in the direction of sliding of the rod 51. The bimetals 613 are configured to drive the rod 51 in sliding, for example during an increase in their temperature.

The rod 51 is here secured to a stop ring 612. An overlap of bimetallic strips 613 has one end in contact with the ring 612 and another end in contact with the bottom cover 625. Thus, during a thermal expansion of the bimetallic stack 613, the assembly formed of the ring 612 and the rod 51 is moved (or exerts a directed effort) downwards in the configuration illustrated in FIG. 6.

The thermal actuator 6 here comprises a return spring 61 1 compressed between the ring 612 and the cover 623, to exert a return force on the ring 612 in a direction opposite to the force generated by the bimetallic strips 613 when their dilatation.

A transmission member 53 is attached to the lower end of the rod 51. The transmission member 53 has for example a spherical shape or cylindrical. The transmission member 53 is slidably mounted in a stirrup 54.

The stirrup 54 belongs to a lever 52 integral with the solar panel 2. The stirrup 54 is eccentric with respect to the pivot axis 24.

During horizontal sliding of the rods 31 and 41, the drive member 53 is driven in horizontal sliding with the same stroke as the rods 31 and 41. Depending on the vertical sliding of the drive member 53, the distance between the drive member 53 and the axis of rotation

24 is modified. Therefore, the lever arm exerted by the drive member 53 on the yoke 52 is modified by the vertical position of the drive member 53. Thus, for the same stroke of the rods 31 and 41, the The pivot angle of the stirrup 52 about the axis 24 is modified by the thermal actuator 6 as a function of the ambient air temperature.

Such a thermal actuator 6 makes it possible to take account of the ambient temperature in order to adapt the pivoting travel of the solar panels 2. The thermal actuator 6 makes it possible, for example, to compensate for a lower ambient temperature in winter, by a greater lever between the drive member 53 and the axis 24, to compensate for greater heat dissipation between the actuators 3 and 4 and the ambient air.

Figure 8 illustrates for example the position of the drive member 53 when the ambient air is colder and bimetals 613 are contracted. The lever arm exerted by the drive member 53 on the yoke 54 is then more important.

FIG. 9 illustrates, for example, the position of the drive member 53 when the ambient air is hotter and the bimetallic strips 613 are expanded. The lever arm exerted by the drive member 53 on the yoke 54 is then smaller.

FIG. 7 is a schematic sectional view of a second variant of mechanical transmission 5. In this variant, the return spring 61 1 is replaced by a thermal actuator 7 sensitive to solar radiation.

In this variant, the thermal actuator 7 is arranged in the alignment of the thermal actuator 6. The thermal actuator 7 comprises a support 72 embedded in the support 62. The rods 31 and 41 therefore also drive the thermal actuator 7 in horizontal sliding.

The support 72 here comprises a side wall 721 and a cover 723. The support 72 advantageously delimits a closed cavity 722. A superposition of thermostatic bimetals 713 is housed inside the cavity 722. The cavity 722 is intended to capture the radiation solar, so that this solar radiation optimally heats the bimetallic strips 713. The cavities 622 and 722 are separated by a wall 55 intended to thermally isolate them. The wall 55 is traversed by the rod 51, and may be used to ensure sliding guidance of the rod 51. The bimetals 713 are deformed as a function of the radiation received by the support 72. A temperature variation of the bimetals 713 leads to a variation of their bulk in the direction of sliding of the rod 51. The bimetals 713 are configured to drive the rod 51 in sliding, for example during an increase in their temperature, in compensation of the forces exerted by the thermal actuator 6 on this rod 51.

The rod 51 is here secured to an abutment ring 712. An overlap of bimetallic strips 713 has one end in contact with the ring 712 and another end in contact with the bottom cover 723. Thus, during a thermal expansion of the stack of bimetallic strips 713, these bimetallic strips 713 exert a compensating force on the rod 51 with respect to the force exerted on this rod 51 by the thermal actuator 6.

An approximate example of sizing of a solar energy recovery system using a mechanical transmission as illustrated in FIG. 7 can be given.

It is assumed that the sun, having an angle of incidence of Θ, applies a power E * sin (Θ) in the cavity 422 through the filtering member 41. It is assumed that the filter member 31 blocks the entry of solar radiation to the cavity 322.

The heat balance of the cavity 422 is E * sin (Θ) = K * S * (T422-T0), with T422 the temperature in the cavity 422, T0 the temperature of the external environment, and taking into account a exchange surface S with the outside and a heat exchange coefficient with the outside of K for this cavity 422.

We can deduce the following relation:

T422 = T0 + (E * sin (Θ)) / (K * S)

For the cavity 322, the thermal balance is 0 = K * S * (T322-T0) with T322 the temperature in the cavity 322. It is therefore deduced that T322 = T0.

With identical bimetallic overlays 313 and 413, the no-load extension laws for these bimetallic superpositions can be expressed with the following relationships:

X41 = A * (T422-T0)

X31 = A * (T322-T0)

With X41 and X31, the respective displacements of the rods 31 and 41. The respective forces of the rods 31 and 41 being in opposition, the effective horizontal displacement X of the actuating member 53 is defined by the following relationship in the present case:

X = A ^* (T422-T0-T322 + T0) = A ^* (T422- - T322) = (A ^* E ^* sin (Θ)) / (K ^* S)

By using thermal actuators 6 and 7 using similar bimetals 613 and 713 and positioned in opposition, the temperature T613 of the bimetallic strips 613 is T0 and the temperature T713 of the bimetallic strips 713 is defined by the following relationship (assuming the same parameters A, K and S for the thermal actuator 7), taking into account a solar power of E ^* cos (Θ) reaching the cavity 722:

T722 = T0 + (E ^* cos (Θ)) / (K ^* S)

Due to the compensation provided by the thermal actuator 6, the vertical displacement of the actuating member 53 can be expressed by the following relation:

Z = (A ^* E ^* cos (Θ)) / (K ^* S)

The pivot angle β of the stirrup 54 (and thus of the solar panel 2) can then be defined by:

β = Arctan (X Z) or β (system orientation angle) = Θ (orientation angle of the sun)

In the examples illustrated, an application has been described for driving a solar panel 2. However, it is also possible to envisage an application to any other solar receiver such as a mirror, configured to send light radiation back to a target, to inside a building or outside.

Claims

System for tracking a light energy source (1), comprising:

-a solar receiver (2) pivotally mounted relative to an axis (24);

-a thermomechanical transducer (3, 4), comprising:

-at least first (3) and second (4) thermal actuators each having at least one thermostatic bimetallic strip deformed according to the solar radiation they receive;

-a first light filtering member (33) surmounting the first thermal actuator (3), said first filtering member having a first optimal direction of incidence, the light power transmitted by the first filtering member decreasing when the incidence of the radiation solar is inclined relative to said first optimal direction of incidence;

-a second light filtering member (43) surmounting the second thermal actuator (4), said second filtering member having a second optimal direction of incidence, the light power transmitted by the second filtering member decreasing when the incidence of the radiation solar is inclined relative to said second optimal direction of incidence, said first and second optimal directions of incidence being different;

-a drive member (31,41) having a sliding direction, the deformations by expansion of the respective bimetallic strips of the first and second thermal actuators (3, 4) biasing said drive member in the sliding direction in opposite directions ;

-a mechanical transmission (5) transforming the sliding of the drive member (31,41) into pivoting of said solar receiver around said axis (24);

Characterized in that the mechanical transmission (5) comprises at least a third thermal actuator (6) with a thermostatically bimetallic strip deformed as a function of the ambient temperature and isolated from solar radiation, the deformation of the bimetallic strip of the third thermal actuator (6) modifying the ratio transmission between the sliding stroke of the drive member and the pivot angle of said solar receiver

(2) around said axis (24).

System according to claim 1, in which said thermal actuators (3, 4, 6) each comprise several thermostatic bimetallic strips (313,413,613) superposed.

3. System according to claim 2, in which said superimposed thermostatic bimetallic strips each form a concave plate at 20°C, the concavities of at least two of said superposed plates having opposite orientations.

4. System according to any one of the preceding claims, in which the deformation of the thermostatic bimetal (613) of said third thermal actuator (6) modifies a lever arm of a force of said drive member (31, 41) requesting the solar receiver (2) pivoting around said axis (24).

System according to claim 4, comprising:

-a lever (52) secured to the solar receiver (2) pivoting around said axis (24);

-a transmission member (53) slidingly integral with said drive member (31,41) and applying a force on said lever (52) at a distance from said axis (24), the deformation of the bimetallic strip of the third thermal actuator (6) moving said transmission member to modify the distance separating said axis from the force applied to said lever.

System according to claim 5, further comprising a fourth thermal actuator (7) with a thermostatic bimetallic strip (713) deformed as a function of the solar radiation it receives, the deformation of the bimetallic strip of the fourth thermal actuator exerting a force opposing the movement of the transmission member (53) when the bimetallic strips of the third and fourth thermal actuators are heated.

System according to any one of the preceding claims, in which said light filtering members (33,43) comprise respective opaque slats (331,431), the slats of the first and second light filtering members having distinct inclinations relative to the direction of sliding of said drive member.

System according to any one of the preceding claims, wherein said thermostatic bimetal (613) of the third thermal actuator is in communication with air at ambient temperature.

System according to any one of the preceding claims, in which the bimetallic strips of the first and second thermal actuators are housed in respective closed cavities (322, 422) absorbing said solar radiation.

10. System according to any one of the preceding claims, wherein said thermostatic bimetal (613) of the third thermal actuator (6) is isolated from solar radiation via a reflective wall.