FR2966917A1 - Solar panel for converting solar energy into e.g. heat energy, has sun tracker comprising axle whose average angular rotating speed, between two half-yearly inversions of rotating direction, is comprised between specific degree per day - Google Patents

Abstract

The panel has a uniaxial sun tracker comprising a single horizontal rotating axle whose average angular rotating speed over a period of six months, between two half-yearly inversions of rotating direction, is comprised between 0.26 and 0.40 degree per day. A solar radiation concentrator is formed of a cylindro-parabolic mirror (13) and/or a Fresnel lens. The rotating axle is oriented parallel to east-west direction. A thermal or photovoltaic solar collector is positioned in a solar radiation concentration zone. An independent claim is also included for a method for orienting a solar panel relative to the Sun.

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a concentrator of solar energy consisting of a mirror and a follower of the uni-axial sun to monitor the solar position.

State of the art Solar collectors are often made of heat-conducting metal plates or tubes and / or photovoltaic cells. These elements that convert the sun's radiation into heat or electric current contain expensive materials, such as crystalline silicon or copper. To reduce the overall cost of solar panels we want to reduce the surface of the solar collectors while keeping the same efficiency of capture. This is possible by concentrating the sunlight on the sensors by concentrating optical means (concentrators) such as Fresnel lenses, mirrors or optical fibers. The use of these concentrators requires to direct the solar panels towards the sun during its daily movement and its seasonal movement; the corresponding devices use mechanical components set in motion by one or more electric motors. There is interest in choosing a method of solar concentration and monitoring of the path of the sun, the cost of materials used is low enough to make the process more profitable than a fixed solar panel without concentration. The calculation of this profitability is generally based on a period of operation of several years in order to integrate averages of sunshine for the place of installation, and to take into account the useful life of the materials and devices used.

Many types of solar concentrators are known.

The document FR 2 353 812 (Bertin) describes a solar thermal energy sensor with several concave cylindro-parabolic mirrors arranged in parallel, each mirror being orientable toward the sun by turning about a longitudinal axis adjacent to the heat receiving tube which occupies the focus of the mirror. For east-west oriented sensors, a daily or weekly calibration device allows the mirror to be oriented manually or automatically.

The document FR 2 339 901 (NASA) describes a device for tracking the daily and seasonal movements of the sun comprising pedestals aligned along the North-South axis supporting a housing inside which there is a circular collector; an energy absorbing element is placed in the collector focus. The housing is rotatably supported by an axis in several sections, in particular a median portion extended on either side by sections perpendicular to the median portion. The medial portion rotates about an axis called the seasonal axis and the end portions rotate about an axis called the daily axis.

The document FR 2 44 852 (Morvan) describes a sun-ray concentration sensor disposed on a support rotating around a first axis AA 'oriented towards the pole star at a constant daily rotation speed of 15 ° per hour. In addition, the sensor is mounted on its support so as to rotate in its support about an axis B-B 'perpendicular to the first at a speed of about 1 ° every 3 days or about 2 ° per week. U.S. Patent Nos. 4,261,335 and 4,548,195 (Balhorn) describe solar energy systems that collect, concentrate, and transmit solar radiation to an energy converter. The apparatus includes non-spherical reflectors pivotally mounted in a holder. The incident radiation strikes the reflector and is sent to the fixed point. Means for adjusting the altitude (pivoting about a vertical axis) and the azimuth (pivoting about a horizontal axis) of the reflectors are provided within the system to keep the solar energy concentrated at the end of the light guides. The adjustment means are controlled by a control unit which sends signals to the drive motors around the respective axes (in particular a microprocessor which stores in memory the desired positions of the reflectors for each day). Each reflector pivots about the axes so as to maintain its focal axis at half the angle made by the sun and the first fixed position corresponding to the reflector during the majority of sunshine hours. US Pat. No. 4,548,195 (Balhorn) describes another embodiment of this system, in which the reflectors are pivotally mounted around a North-South oriented axis and around axes perpendicular to the first axis and actuated by electric motors. controlled by a control unit. The control unit stores in memory the coordinates of the successive positions of the sun and also takes into account a deviation factor which is in function of the day of the year and the geographical coordinates of the place, to control the position of the focal axis of the reflectors. According to this document, the arrangement of the pivot axis relative to the mirror and the application of a deflection factor relative to the theoretical focal axis of the reflector makes it possible to better use the surface of the reflector and to reduce the width. the beam received by the receiver. The document US Pat. No. 5,286,305 (Laing) describes a photovoltaic system supported by a floating platform comprising several modules, each comprising a concentrator and a photovoltaic converter. Each module is connected to a tube that drives the modules in rotation about a vertical axis at the speed of the sun. In order to overcome the vertical displacement of the focal line according to the daily positions of the sun, each module comprises a lens arranged above the photovoltaic cells. This document does not give any indication as to the corrections to apply to adapt the module to the seasonal movements of the sun.

Document US 2008/0295 825 (Kleinwächter) describes a solar energy concentrator system comprising a Fresnel lens oriented along the North-South axis (x) and a conduit oriented according to the focal length. The focal width of the lens varies with the angle (a) which is defined by the daily position of the sun. The document describes a sun tracking system comprising a mechanical system that transforms the geometric conditions into lens displacement to correct the focal width (z) and the y-axis shift. This document gives no indication as to the speed at which the lens rotates.

In order to reduce the cost of the solar panel + follower assembly and to increase the profitability of such a system, the present invention aims to provide a new, simpler solar energy concentrator, which has a reduced solar collector area. and a simplified mechanical part.

Objects of the invention

According to the invention, the problem is solved by a solar panel comprising at least one solar radiation concentrator, at least one photovoltaic and / or thermal solar collector and a uni-axial sun follower, characterized in that said single follower axial axis of sun has a single axis of rotation which is horizontal and whose average rotational angular velocity over a period of six months, between two semiannual inversions of the direction of rotation, is between 0.26 and 1 degree per day, and preferably between 0.26 and 0.40 degree per day. Very preferably, said horizontal axis of rotation is oriented parallel to the East-West direction. Preferably, the rotational speed of the sun follower axis is fixed. The solar panel may be provided with automatic means for rotating about said axis of rotation, but in another embodiment, it comprises simple means for manual adjustment of the orientation of the mirror about its axis of rotation. Advantageously, said solar radiation concentrator comprises a cylindro-parabolic mirror and / or a Fresnel lens. The center of gravity is advantageously located outside the axis of rotation of the sun follower.

Another object of the invention is a method for orienting a solar panel according to the invention with respect to the sun, comprising a periodic adjustment of the orientation by solar input characterized by a fixed angular velocity of between 0.26 and 1 degree. per day that flows between two consecutive adaptations. This adaptation can be done every day. However, it can be done at a reduced frequency, but preferably at least at a weekly frequency. It can be done by manually adjusting the orientation of the mirror. According to the invention, the direction of rotation of the concentrator is reversed to a day which is within an interval of more or less seven days around the solstice, and preferably more or less three days around the solstice, and even more favorite on the solstice day.

Figures The invention is described with reference to Figures 1 to 6 which illustrate embodiments of the invention; they do not limit the invention. Figure 1 shows in section the principle of solar concentration from a half cylindrical-parabolic mirror. Figure 2 shows in section the principle of the pursuit of the sun by a parabolic mirror according to the seasons.

FIG. 3 represents, in the case of a solar concentrator provided with a precise tracking of the sun, an example of a diagram of the positioning of the sun with respect to the horizon and the positioning of the focal point on the solar collector according to the different combinations of dates and times of the year.

FIG. 4 represents, in the case of a solar concentrator according to the invention, the same example of a diagram as the case of FIG. 3, that is a diagram of the positioning of the sun with respect to the horizon and the positioning of the focal length on the solar collector according to the different combinations of dates and times of the year.

FIG. 5 shows in section an exemplary mechanism for the rotation of the solar concentrator according to the invention. Figure 6 shows a solar panel according to the invention.

DETAILED DESCRIPTION OF THE INVENTION The term "solar collector" here means a converter of solar energy into electrical, thermal or chemical energy. Here, the term "solar concentrator" means an optical system capable of concentrating the energy of the sun using at least one mirror.

By "mirror" is meant here a reflective surface, metallic or non-metallic. Here is meant by "sun follower" a mechanical device capable of orienting the solar collector towards the sun and to follow the relative movement of the sun.

The solar concentrator which is the subject of this invention comprises at least one solar concentrator 14 comprising at least one solar energy concentrator mirror 13, at least one solar collector 15 positioned in the zone of concentration of solar radiation, and a single solar tracker. axial.

The shape of the solar concentrator 14, the shape of the mirrors 13 and the dimensions of the solar collector 15 as well as the sun tracking method are chosen so that the solar concentration zone remains at the surface of the solar collector during the displacement of the solar collector. sun in its diurnal movement from East to West. By way of example, the mirror 13 may be of cylindro-parabolic or half-cylindro-parabolic shape and its longitudinal axis oriented from East to West. In order to maintain the solar concentration zone on the surface of the solar collector during the movement of the sun in its seasonal movement along the North-South axis, the solar concentrator 14 pivots about a horizontal axis oriented East-West. The height of the sun when it passes the meridian at noon solar time is a function of the latitude of the place and the time of the year. Its annual amplitude is always 46 °. In the example of a cylindro-parabolic mirror of East-West longitudinal axis, when it is facing the sun, at 12 o'clock, the shape of the focal point on the plane solar collector (Al2, B12, C12) is concentrated, rectilinear and parallel to the longitudinal axis of the mirror, and this whatever the time of the year, so whatever the height of the sun compared to the southern horizon (A, B or C), because the solar concentrator 14 rotates around the axis so that it is always facing the sun. However, the displacement of the sun in its clockwise movement (see FIG. 3) causes a displacement and a deformation of the focal length on the surface of the solar collector 15. This displacement and this deformation depend on the time of the year: For the period of the 21st March to 21 September in the afternoon the displacement of the focal length is down (Al2 to A8) with a deformation which is a spread in width of the luminous flux; and in the morning an upward deformation (A8 to Al2) with a reverse deformation, that is to say a reduction in width of the luminous flux. For the period from 21 September to 21 March in the afternoon the displacement of the focal length is upward (C8 to C12) with a deformation which is a spread in width of the luminous flux; and in the morning a downward deformation (C12 to C8) with an inverse deformation, that is to say a reduction in width of the luminous flux. For the days of March 21 and September 21, which corresponds to the equinoxes, the focal remains fixed (B12 and B8) in the morning as the afternoon. The displacement value of the focal length is L1. This value must correspond to the minimum width of the solar collector.

In the previous embodiment, the solar concentrator 14 is rotated in order to track the sun in its annual displacement, that is to say in its displacement in height at its passage to the celestial meridian. This displacement is done with an average speed of 46 ° in 6 months, or 0.25 ° per day. A reversal of the direction of the sun's movement requires a reversal of the rotation of the solar concentrator 14 on December 21st and June 21st of each year. The method of tracking the solar position used in the device according to the invention consists in increasing the average rotation speed of the solar concentrator. In our example, at 12h on June 21st, by positioning the focal length in the bottom of the solar collector (D12 - Figure 4), and not in the center as in the previous case (Al2 - Figure 3) and applying an average rotation speed greater than 0.25 per day, the focal length will shift and deform during the year due to the gradual angular offset generated by the difference between the actual speed of the sun's movement and the accelerated speed of the solar concentrator. The focal length (D12) at 12 o'clock, over the period from June 21st to December 21st, will progressively move towards the top of the solar collector 15, and deform in the direction of an enlargement of the luminous flux (E12 - F12). Between 21 December and 21 June the direction of rotation of the solar concentrator 14 is reversed, as is the direction of movement of the sun, and the process of displacement and modification of the focal length is also reversed so that the focal point resumes its position. and its initial form on June 21 of the following year. The displacement and the deformation of the focal length during this cycle of accelerated tracking of the sun is a function of the average rotational speed of the solar concentrator 14. By fixing for example the speed at 70 ° for 6 months, an average of 0, 38 ° per day, we can observe that the displacement and the deformation of the focal length, even during the extreme hours of the day (Figure 4 D8 - E8 - F8), require much less surface of solar collector 15 than with a speed average rotation of 0.257 ° per day. In our example, with an average speed of 0.38 ° per day, L2 is the width of the solar collector needed to receive the maximum luminous flux. L2 is half of L1. The reduction of the surface of the solar collector thus makes it possible to reduce its cost. This is particularly the case for solar cells such as silicon photovoltaic cells and / or cells adapted to solar concentration. The astronomical positioning charts of the sun (Figure 3 and 4) show that the speed of movement of the sun in its annual run at 12 o'clock is not regular.

It varies between 0.13 ° per day on average for the months of December and June, and 0.43 ° per day on average for the months of March and September. Conventional sun tracking systems take into account these differences in speed during the year to better adjust the angular position of the solar panels. Their actual speed is therefore not constant. This adjustment requires sophisticated automatic means. For the solar concentrator 14 object of this invention, one can use a rotational movement whose average speed during the year is higher than the average speed of the sun. However, the actual speed associated with the method that is the subject of this invention can be either variable or constant during the entire annual run of the sun, which makes another difference with conventional systems whose rotational speed is based on the actual speed of movement of the sun. which is not constant. This rotation is also very slow the rotation of the solar concentrator can be done manually for example by increments of 2.6 ° every week. In a semi-automatic mode of operation, and to give a non-limiting example, the rotation of the solar concentrator uses the force of gravity acting at the center of gravity 11 of the solar concentrator, to perform this rotation and to actuate a speed controller mechanical. In a non-limiting example (see FIG. 5), the solar concentrator 14 is fixed on an axis of rotation 12 that is off-center with respect to its center of gravity 11. The weight of the panel rotates the assembly about the axis 12 with a speed which is set at 0.38 ° per day and regulated by a mechanical clock 18 containing a set of gears and a rocker 16. In another example, not shown, the speed regulation is by a reservoir containing a liquid and a float on the surface of this liquid; the flow rate of this liquid is regulated by a calibrated orifice which causes a gradual and constant decrease in the level of the liquid and therefore the float which is connected to the solar concentrator. It can thus be seen that the method according to the invention for orienting the concentrator towards the sun can use means to ensure the rotation of the concentrator about the horizontal axis which are simpler than automatic means, for example semi-automatic or even manual . Indeed, knowing that a solar panel installation in any case requires regular monitoring and maintenance, the adjustment of the position of the panels or concentrators can be done by manual means.

In a particular mode of manufacture a solar panel 17 is constituted by a set of solar concentrators 14. The uni-axial tracking of the sun of all the solar concentrators according to the invention is then done by the rotation of the solar panel around a single horizontal axis oriented East West 12.

This invention is particularly suitable for the production of photovoltaic electricity and / or the production of solar hot water.

We describe here an embodiment which is shown schematically in FIG. 6. A solar concentrator panel according to the invention consisting of ten photovoltaic modules and ten parabolic aluminum mirrors of thickness 0.5 mm and of which the curvature has for equation y = x2 / 4f where f represents the focal length which is 4 cm, and X takes values between 2 and 18 cm. The width of each mirror is then 30 cm. Its length is fixed at 120 cm. Each mirror has been placed at each of its ends on a shape guide 20 which maintains the good parabolic curvature of the mirror. The shape guides 20 contain a support 21 for the photovoltaic modules. This module support is flat and forms a 45 ° angle with the straight line joining the linear edges of the mirrors. The photovoltaic modules were rectangular with dimensions of 100 x 8 cm. Their thickness is 15 mm. They include a finned radiator on their nonactive rear face (not shown in the figure). The photovoltaic modules are fixed on their support 21, the active face is oriented towards the mirror, the lower part is positioned at a distance of 5 cm from the low end of the mirrors. The ten mirrors and the ten modules are aligned so as to form a solar concentrator panel consisting of two rows of 5 mirror couples plus module. The panel is movable about a horizontal axis of rotation 12 consisting of a steel tube 40 mm in diameter and 2 meters in length. This tube is parallel to the longitudinal axis of the mirrors and passes through the shape guides 20 of the panel. Each end of the tube rests on a vertical upright 22 of 1.20 m in height and fixed to the ground by a foot 23. The panel and the mirrors are oriented to the south, the axis of rotation is oriented East / West.

In the Northern Hemisphere, on June 21st at 12am solar time, the sun in the South is at its maximum height. The solar panel is inclined so that the straight focal length is positioned in the bottom of the photovoltaic modules. During the day the focal length moves and changes while remaining on the surface of the photovoltaic module. Every week, and until December 21, the panel is manually rotated around its axis of rotation at an angle of 2.6 ° to the southern horizon. From 21 December the pivoting of the panel is carried out in the opposite direction, towards North, always of 2,6 ° per week and until resuming its initial position of June 21. The rotation of the panel will have been 67.6 degrees over a period of 6 months, an average speed of 0.37 ° per day; while the sun during the same period will have traveled only 46 ° with an average speed of 0.25 ° per day. The difference in rotation speed of the panel with respect to the speed of displacement of the sun made it possible to maintain the focal length on only 5 cm of photovoltaic module width whereas with a rotation speed of the panel identical to that of the sun it would have been necessary a module width of 10 cm to obtain the same result. The gain in

Claims (10)

REVENDICATIONS1. Solar panel (17) comprising at least one solar radiation concentrator (14), at least one photovoltaic and / or thermal solar collector (15) and a uni-axial sun follower, characterized in that said uni-axial sun follower has a single axis of rotation (12) which is horizontal and whose average rotational angular velocity over a period of six months, between two semiannual inversions of the direction of rotation, is between 0.26 and 1 degree per day, and preferably between 0.26 and 0.40 degree per day. 2. solar panel (17) according to claim 1 characterized in that the rotational speed of the axis of the sun follower is fixed. 3. Solar panel (17) according to claim 1 or 2, comprising automatic means (18) for rotating about said axis of rotation (12). 4. Solar panel (17) according to one of claims 1 to 3, characterized in that said axis of rotation (12) horizontal is oriented parallel to the East-West direction. 5. solar panel (17) according to any one of claims 1 to 4, characterized in that said solar radiation concentrator (14) comprises a cylindro-parabolic mirror (13) and / or a Fresnel lens. 6. solar panel (17) according to any one of claims 1 to 5, characterized in that its center of gravity (11) is located outside the axis of rotation (12) of the sun follower. 7. A method for orienting a solar panel (17) according to any one of claims 1 to 6 relative to the sun, comprising a periodic adaptation of the orientation relative to solar radiation characterized by a fixed angular velocity of between 0.26 and 1 degree per day that flows between two consecutive adaptations. 8. Method according to claim 7, characterized in that said adaptation is made at least at a weekly frequency. 11 9. The method of claim 7 or 8, characterized in that said adaptation is made by a manual adjustment of the orientation of the mirror (13). 10. Method according to one of claims 7 to 9, characterized in that the direction of rotation of the concentrator (4) is reversed to a day which is within an interval of plus or minus seven days around the solstice, and so preferred more or less three days around the solstice, and even more preferably the day of the solstice.10