Stationary sunlight redirecting system for increasing the efficiency of fixed-tilt PV farm
View Patent ↗A low-cost system for increasing the electricity generation of flat panel photovoltaic (PV) farms in which sunlight redirecting elements are positioned in offset spaces provided between adjacent panel assemblies and serve to redirect otherwise unused sunlight onto solar cells disposed on one of the panel assemblies. The redirecting elements are located in a prismatic volume bounded at its upper end by an inclined upper plane that extends across the offset space separating adjacent PV panel assemblies. The redirecting elements are either mounted to at least one of the PV panel assemblies, or placed on the ground between the assemblies. Each redirecting element includes multiple reflecting and/or refracting surfaces that utilize a disclosed microoptical arrangement (e.g., focus and steer or reorient and scatter) to distribute the redirected sunlight in a substantially homogenous (uniform) distribution on the solar cells.
1. A stationary sunlight redirecting system for increasing the efficiency of a fixed-tilt PV farm, the fixed-tilt PV farm including a plurality of PV panel assemblies, each PV panel assembly including a plurality of solar cells arranged in a substantially planar array between a corresponding upper horizontal edge and a corresponding lower horizontal edge such that the solar cells form an active region that is parallel to the substantially planar array, the planar array of the plurality of PV panel assemblies being maintained in an inclined angle relative to ground, wherein each adjacent pair of said PV panel assemblies is disposed at a predetermined spacing such that a prismatic volume is defined between each adjacent pair of said PV panel assemblies, each prismatic volume being disposed below an upper plane extending between the upper horizontal edge of a first PV panel assembly of said adjacent pair and the lower horizontal edge of a second PV panel assembly of said adjacent pair, wherein the sunlight redirecting system comprises:
a sunlight redirecting element including a base and a plurality of substantially identical redirecting structures uniformly arranged and fixedly disposed on the base, each redirecting structure including a plurality of corresponding parallel elongated optical surface regions fixedly oriented substantially parallel with the upper horizontal edge of said PV panel assembly and disposed such that sunlight is redirected along substantially identical diverging paths such that the redirected sunlight is directed away from said sunlight redirecting element in a substantially homogenous pattern; and
means for securing the sunlight redirecting element in said prismatic volume between said first PV panel assembly and said second PV panel assembly such that the redirected sunlight is directed onto the active region formed by the plurality of solar cells disposed on the second PV panel assembly.
2. The stationary sunlight redirecting system according to claim 1 , wherein the prismatic volume is further defined by a front plane, a rear plane, and ground disposed between the adjacent PV panel assemblies,
wherein the front plane extends between ground and the lower horizontal edge of a second PV panel assembly the front plane being inclined at an angle defined by the active region of the solar cells that are mounted on the second PV panel assembly,
wherein the rear plane extends between ground and the upper edge of the first panel assembly, the rear plane being inclined at an angle defined by an expected sunlight direction at noon on the summer solstice, and
wherein said means for securing the sunlight redirecting element in said prismatic volume includes means for securing the sunlight redirecting element between said front and rear planes and over said ground.
3. The stationary sunlight redirecting system according to claim 1 , wherein said means for securing the sunlight redirecting element includes means for securing the sunlight redirecting element in said prismatic volume such that the redirecting element receives and redirects sunlight onto the active region formed by the plurality of solar cells disposed on the second PV panel assembly during a period of at least one month.
4. The stationary sunlight redirecting system according to claim 1 ,
wherein the second PV panel assembly has a length defined by opposing first and second side edges, and
wherein the sunlight redirecting element extends substantially the entire width of the second PV panel assembly.
5. The stationary sunlight redirecting system according to claim 4 ,
wherein said means for securing the sunlight redirecting element includes a bracket for securing the sunlight redirecting element onto the first PV panel assembly such that the redirecting element extends from the upper horizontal edge of the first PV panel assembly into the prismatic volume defined between the first and second PV panel assemblies.
6. The stationary sunlight redirecting system according to claim 4 ,
wherein said means for securing the sunlight redirecting element includes a bracket for securing said sunlight redirecting element onto the second PV panel assembly such that the element extends from the lower horizontal edge of the second PV panel assembly into the prismatic volume defined between the first and second PV panel assemblies.
7. The stationary sunlight redirecting system according to claim 4 ,
wherein said means for securing the sunlight redirecting element includes a structure for fixedly supporting said sunlight redirecting element over the ground disposed between the first PV panel assembly and the second PV panel assembly.
8. The stationary sunlight redirecting system according to claim 1 , wherein the plurality of corresponding parallel elongated optical surface regions of each of the plurality of substantially identical redirecting structures comprises passive means for redirecting said sunlight such that, in yearly aggregate, the sunlight redirecting element redirects 1.3 time more sunlight onto the solar cells than a perfect Lambertian scatterer having an area equal to that of the sunlight redirecting element.
9. The stationary sunlight redirecting system according to claim 1 , wherein the plurality of corresponding parallel elongated optical surface regions of each of the plurality of substantially identical redirecting structures comprises passive means for redirecting said sunlight in a direction that is substantially independent of an incident direction of the sunlight received by the sunlight redirecting element during at least one month of each year.
10. The stationary sunlight redirecting system according to claim 1 , wherein said plurality of corresponding parallel elongated optical surface regions of each said redirecting structure are cooperatively formed and arranged such that, at least some of said parallel sunlight beams directed into said prismatic volume along an incident direction and onto the plurality of redirecting structures are transmitted between the plurality of corresponding parallel elongated optical surface regions of each said redirecting structure, and redirected from the plurality of corresponding parallel elongated optical surface regions toward said active region formed by the plurality of solar cells disposed on the second PV panel assembly.
11. The sunlight redirecting system of claim 10 , wherein said base of the redirecting element comprises a planar substrate, and said plurality of substantially identical redirecting structures are oriented identically and disposed on the planar substrate such that said redirected sunlight is directed along said substantially identical diverging paths toward said active region.
12. The sunlight redirecting system of claim 10 , wherein each of the plurality of corresponding parallel elongated optical surface regions of each redirecting structure comprises at least one of a light reflecting surface, a light refracting surface, a light scattering surface, a light diffractive surface, a holographic optical surface, and a gradient index optical surface.
13. The sunlight redirecting system of claim 10 , wherein each of said plurality of parallel elongated optical surface regions of each said redirecting structure comprises a parabolic cylinder having a first curved optical surface region and a corresponding second curved optical surface region arranged such that sunlight directed onto the first curved optical surface region is redirected onto the corresponding second curved optical surface region.
14. The sunlight redirecting system of claim 13 , wherein said first and second curved optical surface regions of each of said redirecting structure comprise a first curved reflective surface region and a second curved reflective surface region arranged such that sunlight directed onto the first curved reflective surface region is reflected by said first curved reflective surface region directly onto the second curved reflective surface region.
15. The sunlight redirecting system of claim 14 ,
wherein the base of each said sunlight redirecting element comprises a transparent material layer having a planar upper surface and an opposing lower surface, and
wherein the corresponding first and second curved reflective surface regions of each said plurality of redirecting structures are disposed on the lower surface of the transparent material layer and are arranged such that said sunlight directed along the incident direction onto an associated first region of the planar upper surface is refracted onto said first curved reflective surface region, and sunlight that is reflected by the corresponding second curved reflective surface region is directed through the planar surface to the active region.
16. The sunlight redirecting system of claim 13 ,
wherein each said sunlight redirecting element further comprises a transparent material layer having an upper surface, and
wherein said first curved optical surface region and said corresponding second curved optical surface region of each said sunlight redirecting element comprise respective first and second elongated parabolic cylindrical sections of the upper surface of the transparent material layer.
17. The sunlight redirecting system of claim 10 ,
wherein said plurality of corresponding optical surface regions of each of said redirecting elements comprises a plurality of planar optical surface regions arranged in a sawtooth pattern,
wherein each redirecting structure includes a first planar reflective surface region of said plurality of planar optical surface regions and a second planar scattering surface region of said plurality of planar optical surface regions, and
wherein said each redirecting structure is arranged such that sunlight directed onto the first planar reflective surface region is reflected onto the corresponding second planar scattering surface region.
18. A fixed-tilt PV farm comprising:
a plurality of PV panel assemblies, each PV panel assembly including a panel support structure and a plurality of solar cells arranged in a substantially planar array between an upper horizontal edge and a lower horizontal edge of the panel support structure such that the solar cells form an active region that substantially covers a surface of the panel support structure, the planar arrays of the plurality of PV panel assemblies being maintained in an inclined angle relative to ground, wherein each adjacent pair of said PV panel assemblies is disposed at a predetermined spacing such that a prismatic volume is defined between each adjacent pair of said PV panel assemblies, each prismatic volume being disposed below an upper plane extending between the upper horizontal edge of a first PV panel assembly of said adjacent pair and the lower horizontal edge of a second PV panel assembly of said adjacent pair; and
a stationary sunlight redirecting system for increasing the efficiency of the fixed-tilt PV farm, the redirecting system including a sunlight redirecting element disposed in said prismatic volume between said first PV panel assembly and said second PV panel assembly such that said sunlight redirecting element remains fixed relative to the first and second PV panel assemblies, said sunlight redirecting element including a plurality of parallel elongated parabolic cylindrical optical surface regions that are oriented in parallel with the upper horizontal edge and disposed such that sunlight is redirected along substantially identical diverging paths away from said sunlight redirecting element, wherein said plurality of optical surface regions are collectively arranged such that sunlight entering said prismatic volume is redirected and distributed by said plurality of optical surface regions in a substantially homogenous pattern on the active region formed by the plurality of solar cells disposed on the second PV panel assembly.