Patent Application
20190341881
This application claims priority from French Patent Application No. 18 53877 filed on May 4, 2018. The content of this application is incorporated herein by reference in its entirety.
This invention relates to the field of photovoltaic solar energy, and in particular to systems comprising bifacial photovoltaic solar cells.
The invention applies in particular to systems intended to be installed on the ground or on roofs of buildings.
From prior art, it is known to produce systems comprising photovoltaic solar cells with a bifacial nature, with these cells being grouped together within photovoltaic panels. The interest of such cells resides in the fact that they define two opposite absorption surfaces, for example on the front face a direct absorption surface intended to absorb solar radiation energy, and, on the rear face, an indirect absorption surface also intended to absorb solar radiation energy.
Several realisations have already been considered for obtaining this type of system. Document CN 204993212 is for example known, wherein is described systems provided with panels that comprise bifacial photovoltaic cells, extended downwards by reflectors. Each reflector is inclined in order to allow for the irradiation of the rear surface of the cells of another system located more to the front. This type of design nevertheless has many disadvantages, among which in particular the necessity of having a system engage with at least one other system located in the front, so as to illuminate its rear indirect absorption surface. The use of this type of system thus remains confined to solar power stations that have a plurality of rows of systems. In addition, the distance between each row becomes a parameter that depends on this need for irradiation of the rear surface by the systems of the rear row, in such a way that the space on the ground of the power station may be non-optimised. The same applies for the space along the vertical direction, due to the necessity of providing frames that are sufficiently raised to make it possible to install the reflectors at the bottom of the solar panels.
These same disadvantages are found on other systems, comprising two mirrors symmetrically arranged under the photovoltaic panels, in order to illuminate the indirect absorption surface thereof. Indeed, a vertical offset of these mirrors is required so as to authorise the amplitude in rotation required to follow the path of the sun, all throughout the day. In case of a vertical offset that is insufficient of the mirrors, the latter are able to limit the course of rotation of the rotating unit that comprises the photovoltaic panels and the mirrors, by interacting with the roof or with the ground on which the system rests. Furthermore, when the rotating unit is inclined on the side of one first of the two symmetrical mirrors in order to best direct its direct absorption surface with respect to a sun low in the sky, the second mirror is then in a position that generates a shadow that is detrimental for the directly consecutive system in the row of the solar power station concerned. In order to prevent this shading which is all the more so consequent when the sun is low, the systems of the same row can be spaced apart. However, this spacing of the systems generates a non-optimised rate of occupation of the ground or of the roof, with for consequence an energy potential that can be improved with respect to the square metres available.
The invention therefore has for purpose to remedy at least partially the disadvantages mentioned hereinabove, concerning the realisations of prior art.
To do this, the invention first of all has for object a photovoltaic solar energy system comprising:
a base structure;
a rotating unit;
a rotation connection between the rotating unit and the base structure, the rotation connection defining a pivot axis of the rotating unit,
the rotating unit comprising:
a set of bifacial photovoltaic solar cells, jointly defining two opposite surfaces intended to absorb energy from solar radiation;
a support frame of said cells, the frame comprising at least one offsetting arm of the cells with respect to the base structure, a low end of the offsetting arm being connected to the rotation connection;
two mirrors each defining a reflector surface configured to reflect the light in the direction of the set of cells, preferably in the direction of an indirect absorption surface of this set, the two mirrors being arranged respectively on either side of the offsetting arm.
According to the invention, at least one of the two mirrors is mobile by having a first end pivotably mounted on a means sliding along the offsetting arm, the sliding means able to be displaced between a high position bringing the mobile mirror into a configuration of maximum extent, and a low position bringing the mobile mirror into a configuration of minimum extent wherein a second end of the mobile mirror, opposite the first end, is located closer to the offsetting arm than in the configuration of maximum extent.
Thus, the invention relates to a system with at least one of the two mirrors, and preferably both of them, having a retractable nature. Indeed, at the same as its first end is moving downwards along the offsetting arm, the mobile mirror tends to close with its second opposite end which approaches this same arm. Consequently, when the rotating unit is inclined on the side of one of the two mirrors, for example in order to best direct its direct absorption surface with respect to a sun low in the sky, the second mirror can then adopt the configuration of minimum extent or a configuration close to the latter, so as to limit the induced shading on the directly consecutive system in the row of the solar power station concerned.
The systems of the same row can then be brought closer to one another, as such optimising the occupation of the ground or of the roof, and consequently increasing the energy potential with respect to the square metres available. As an example, it has been determined that by implementing the principle of retractable mirrors on the systems of a row of a solar power station, the number of systems within this row could be increased by at least 75%.
Furthermore, the mirror located on the side where the rotating unit is inclined can also be folded to limit the interactions with the ground or the roof. Therefore, the length of the offsetting arm of the rotating unit can be decreased, with for consequence a gain in terms of mass and vertical space, while still authorising the tracking of the sun all throughout the day.
The invention also provides the following optional characteristics, taken separately or in combination.
The support frame also comprises a frame fixed on a high end of the offsetting arm, and a connection device is provided between each mobile mirror and the frame of the support frame, this connection device comprising a member sliding along the mobile mirror, as well as a pivot member allowing for a rotation of the sliding member in relation to the frame.
Preferably, the frame is substantially parallel to the set of bifacial photovoltaic solar cells, the frame being interposed between the two mirrors and the set of cells.
The support frame also comprises a plurality of frameworks connecting the frame to the set of bifacial photovoltaic solar cells.
The mobile mirror defines an acute mirror inclination angle with a plane orthogonal to the set of bifacial photovoltaic solar cells, the acute mirror inclination angle being between 5 and 30° in the configuration of minimum extent, and between 65 and 80° in the configuration of maximum extent.
The two mirrors are mobile, and arranged to be displaced symmetrically or asymmetrically.
According to a possibility, the two mobile mirrors are arranged in such a way as to be displaced symmetrically, the first end of each one of them being pivotably mounted on the same means sliding along the offsetting arm.
According to another possibility, the two mobile mirrors are arranged in such a way as to be displaced asymmetrically, the first end of each one of them being pivotably mounted respectively on two separate means sliding along the offsetting arm.
The set of bifacial photovoltaic solar cells can be configured to be displaced laterally on the side of one of the two mirrors, and on the side of the other mirror. In this case, it is for example provided that the support frame comprises a device with a deformable parallelogram designed to laterally displace the set of bifacial photovoltaic solar cells. Alternatively, it can be a simple means of translation of the set of cells, without leaving the scope of the invention.
The system comprises also at least one first actuator of the rotation connection between the rotating unit and the base structure, as well as at least one second mobile mirror actuator, with the first actuator or actuators being separate from the second actuator or actuators.
Alternatively, the system comprises a common actuator that simultaneously controls the rotation connection between the rotating unit and the base structure, as well as each mobile mirror.
The invention also has for object a solar power station that comprises at least one row of photovoltaic solar energy systems such as the one described hereinabove, with the pivot axes of the rotating units belonging to the systems of the row considered, being parallel to each other.
The power station preferably comprises several rows of photovoltaic solar energy systems.
Finally, the invention has for object a method for controlling such a solar power station, implemented in such a way that during the course of a day, the rotating unit of the systems of each row is pivoted from an extreme morning position wherein the unit is inclined on the side of a first of the two mirrors, to an extreme evening position wherein the rotating unit is inclined on the side of one second of the two mirrors, passing through a vertical median position of the rotating unit, with the method also implemented in such a way that for at least one of the systems of at least one of the rows:
the first mobile mirror is displaced from its configuration of minimum extent to its configuration of maximum extent when the rotating unit is displaced from the extreme morning position to its vertical median position, and/or the first mobile mirror is displaced from its configuration of maximum extent to its configuration of minimum extent when the rotating unit is displaced from its vertical median position to the extreme evening position;
and/or
the second mobile mirror is displaced from its configuration of minimum extent to its configuration of maximum extent when the rotating unit is displaced from the extreme morning position to its vertical median position, and/or the second mobile mirror is displaced from its configuration of maximum extent to its configuration of minimum extent when the rotating unit is displaced from its vertical median position to the extreme evening position.
Other advantages and characteristics of the invention shall appear in the non-limiting detailed description hereinbelow.
This description will be given with regards to the accompanying drawings among which;
In reference first of all to
In reference to
In the embodiment of
The set of cells 4 is an integral part of a rotating unit 10, also known as a tracker. Other components are provided on this rotating unit 10, and shall be described hereinafter. The rotating unit 10 thus remains connected to the ground 14 using the base structure 16, carried out using several uprights 18 supporting a beam 20. The beam 20 is preferably of circular section, in such a way as to be able to install a rotation connection 22 between this beam 20 and the rotating unit. The rotation connection 22 defines a pivot axis 24 of the unit 10, with this axis 24 being preferably the one of the beam 20. In this respect, it is noted that the rotation connection 22 provides the unit 10 with the capacity to pivot relatively to the base structure 16, so as to be aligned with the sun all throughout the day. Thus, the pivot axis 24 is directed and inclined according to the latitude of the location of the systems 2. For example, for a latitude of 45.6° N, the pivot axis 24 can be oriented North-South, and inclined towards the south by an angle of about 30° in relation to the horizontal. This angle is frozen, or in another embodiment it can be controlled in order to constantly track, or in defined intervals of time, the change in the position of the sun in the sky during the course of the year. Within the same row la of the power station, the systems 2 have pivot axes 24 that are preferably parallel between them.
The rotating unit 10 also comprises a support frame 26 intended to support the panels of cells 4. This frame 26 first of all comprises one or several offsetting arms 28, arranged preferably orthogonally to the set of cells 4. These arms 28 are spaced apart from one another along the system 2, by falling for example in the same vertical plane as the uprights 18, when the unit 10 adopts its vertical median position such as shown in
The high end 28b of each arm supports a frame 30 of the frame 26. This frame 30, parallel to the set of cells 4 and extending over a similar surface, is perforated to the maximum in order to allow for the passage of the rays reflected on the ground in the direction of the indirect absorption surface 8, such as shall be detailed hereinafter. It is conventionally formed by uprights and crosspieces, and it carries at its periphery a plurality of frameworks 32 connecting this frame to the set of cells 4. These frameworks 32 allow for an additional offsetting of the cells 4 with respect to the base structure 16.
Finally, the rotating unit 10 comprises two mirrors 34, which, in this preferred embodiment, both have a mobile nature within the unit. However, a single one of these two mirrors could be mobile and the other fixed, without leaving the scope of the invention.
The two mobile mirrors 34 are substantially flat, and arranged in such a way as to be displaced symmetrically in relation to a median plane P1 of the unit, wherein the offsetting arms 28 fall. The two mobile mirrors 34, arranged respectively on either side of the arms 28, as such that the frame 30 is vertically interposed between these mirrors and the cells 4. Together, they form a V of which the opening is controlled, as shall be detailed hereinafter. The two surfaces inside the V are reflector surfaces 38 configured to reflect the light in the direction of the indirect absorption surface 8 of the cells 4, such as diagrammed by the light rays R2 in
The mobile mirrors 34 can be carried out by reflectors, for example used in the field of photography, rather than by more expensive mirrors used in the field of CPV (concentrated photovoltaics). The reflection coefficient can be with a range of 88-90%. By way of example, an aluminium plate can be used, about 1 mm thick, or a glass plate whereon is made a deposit of aluminium. According to a possibility, a reflective canvas can be used, for example a sheet of polymer of the PVF, PVDF, PET, etc. type, by using a frame with straps in order to maintain the flatness of reflector surface 38.
Each mobile mirror 34 has a first end 40 in the form of an edge parallel to the pivot axis 24, and which is pivotably mounted according to an axis 43 on at least one means 42 sliding along an offsetting arm 28. Preferably, a sliding means 42 can be provided on several of the arms 28, even over all of them. In this case, the edge 40 which forms the first end of the mirror 34 is pivotably mounted on each one of these sliding means 42, optionally using tabs coming from this edge 40 and forming an integral part of an axis pivot connection 43. In addition, it is preferably here arranged that on each offsetting arm 28 concerned, the sliding means 42 are common with the two mirrors 34, each one pivotably mounted on this means 42.
The first end 40 of each mirror 34 corresponds to its most inward edge within the rotating unit 10, and is therefore opposite a second free end 41 that corresponds to a parallel outer edge. Between these two ends 40, 41 of each mirror 34, the latter is connected to the periphery of the frame 30 by a connection device 44 of which the design allows the mirror to vary the inclination thereof, when its first end is displaced along the offsetting arms 28. More precisely, the connection device 44 comprises a member 48 sliding along the reflector surface 38 of the mobile mirror 34, for example in a rail 50 diagrammed in
When the unit 10 adopts its vertical median position such as shown in the
This configuration of maximum extent defines a maximum active width “Lm” of each mirror, with this width corresponding to the portion of the mirror protruding laterally from the frame 30. On the other hand, the other portion of the mirror located between the connection device 44 and the first end 40 remains inactive, and can optionally be non-reflective. However, the inactive portion is preferably perforated in such a way as to allow light rays R3 referenced in
In this same figure, several dimensions of the system are referenced, among which the maximum active width “Lm” of each mirror, preferably between 2 and 4.5 m. Furthermore, the separation distance “D” between the frame 30 and the indirect absorption surface 8 of the cells 4 is between 1 and 3 m.
The system 2 also comprises means for rotating the unit 10, and for varying the amplitude of the mirrors 34. To do this, in the embodiment described, a first actuator or a first group of actuators 60 is provided, making it possible to control the rotation connection 22 between the unit 10 and the base structure 16. The amplitude of rotation allowed by these first actuators 60, on either side of the vertical median position of
The system 2 also comprises a second actuator or a second group of actuators 62, that make it possible to control the opening/the amplitude of the mobile mirrors 34. The actuators 62 make it possible to displace each sliding means 42 from bottom to top and from top to bottom, along the associated arm 28. This can for example be a linear motor, or a simple cylinder.
In this preferred embodiment, the first actuators 60 are separate from the second actuators 62. However, as the opening of the mirrors 34 is directly correlated with the inclination of the rotating unit about the pivot axis 24, these actuators 60, 62 are synchronised.
According to an alternative embodiment shown in
Since this position is adopted in the morning when the sun is low, the two mirrors 34 then adopt a position of maximum extent, wherein the acute angle of inclination A between the reflector surface 38 and the plane P1 is preferably between 5 and 30°, although a higher value can be retained. In this configuration, the second end 41 of the two mirrors 34 is closer to the arm 28 and to the plane P1 than in the configuration of maximum opening.
In addition, in this configuration of minimum extent, each mirror 34 is lowered due to the displacement of its first end 40 downwards of the offsetting arm 28, via the sliding means 42 brought to the low position by the second actuators. Therefore, the shading induced by the second mirror 34, the farthest to the left in
In this configuration, each one of the two reflector surfaces 38 reflects the light rays R2 on the other of the two surfaces 38, before these rays impact half of the indirect absorption surface 8 with the same incidence. In certain cases, the low opening of the mirrors could not allow for the illumination of the entire surface 8 using reflected rays R2. In this case, the illumination of the indirect absorption surface 8 would in any case be completed by the light rays R3, described hereinabove in reference to
Thus, during the day, the systems 2 of each row la are controlled by the first actuators in such a way that their rotating units 10 are each pivoted from the extreme morning position of
Durant this displacement between the two aforementioned extreme positions, the rotating unit 10 transits through the vertical median position of
According to another embodiment shown in
A similar situation is retained in the extreme morning position shown in
During the daily rotation of the unit 10, the displacement control of the two mirrors 34 is adapted in such a way as to obtain the openings shown for the extreme positions in
Finally, it is noted that in this preferred embodiment, or in the preceding one, the set of cells 4 is also provided to be laterally displaced on the side of the second mirror. More precisely, in the extreme evening position, the set of cells 4 is no longer symmetrical with respect to the plane P1, but transversally offset towards the side of the second mirror in order to limit the shading induced on the directly consecutive system 2.
Inversely, in the extreme morning position, the set of cells 4 is no longer symmetrical with respect to the plane P1, but transversally offset towards the side of the first mirror in order to limit the shading induced on the directly consecutive system 2. In other terms, during the daily rotation of the unit 10, an additional control allows for putting into motion the set of cells 4 in such a way that it is displaced from an extreme position on the side shown in
In order to allow for this displacement of the set of cells 4, a simple translation connection is possible, but the implementing of a device 70 with a deformable parallelogram preferred. The frame 30 and the set of cells 4 then form two opposite sides of the parallelogram, while the frameworks 32 fulfil the function of the two other opposite sides of this parallelogram. For the actuating, one or several other actuators are implemented, or a specific translation movement device is retained, controlled by one or several other actuators of the system 2.
Of course, various modifications can be made by those skilled in the art to the invention which has just been described, solely by way of non-limiting examples. In particular, the characteristics of the various embodiments can be combined together. Furthermore, it is noted that the arrangement of the plane of the cells with respect to the frame is not limited to that of the examples described hereinabove, but this relative arrangement can be of any arrangement. The plane of the cells could thus be inclined by an angle different from 90° with respect to the plane of the offsetting arms 28. This angle could even be zero, leading to a parallelism or to an identity between the plane of the cells 4 and that of the arms 28. In this latter case, only one of the two reflector surfaces 38 of the two mirrors 34 is provided to reflect the light in the direction of the indirect absorption surface 8 of the cells 4, the other surface 38 being configured to reflect the light in the direction of the direct absorption surface 6.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1853877 | May 2018 | FR | national |
