Passively cooled solar concentrating photovoltaic device
View Patent ↗A Cassegrain-type concentrating solar collector cell includes primary and secondary mirrors disposed on opposing convex and concave surfaces of a light-transparent (e.g., glass) optical element. Light enters an aperture surface surrounding the secondary mirror, and is reflected by the primary mirror toward the secondary mirror, which re-reflects the light onto a photovoltaic cell. The photovoltaic cell is mounted on a central portion of heat spreader that extends over the primary mirror. The heat spreader transmits waste heat from the photovoltaic cell in a manner that evenly distributes the heat over the optical element, thereby maximizing the radiation of heat from the aperture surface into space. The heat spreader includes a thick copper layer formed on a flexible substrate (e.g., polyimide film) that is patterned with radial arms that facilitate mounting onto the convex surface of the optical element.
1. A concentrating photovoltaic (CPV) device comprising:
a photovoltaic (PV) cell;
a solid, light-transparent optical element having a first side including a convex surface and a second side including a substantially flat aperture surface and a curved surface in a central portion of the second side, wherein the curved surface is smaller than the convex surface;
a primary mirror disposed on the convex surface and a secondary mirror disposed on the curved surface, the primary and secondary mirrors defining a focal region at which light received by the optical element is concentrated, wherein the PV cell is located in the focal region; and
a heat spreader in thermal contact with the optical element and having a central portion disposed over the center of the convex surface of the optical element and one or more peripheral portions extending from the central portion over the first side,
wherein the heat spreader comprises a thermally conductive material that is in contact with and conformally disposed over a back surface of the primary mirror such that heat generated at the focal region is passively transmitted from the heat spreader through the primary mirror and the optical element for radiation from the substantially flat aperture surface.
2. The CPV device according to claim 1 ,
wherein the heat spreader has a lateral thermal resistance extending from the central portion to the peripheral portions,
wherein the optical element has a transverse thermal resistance extending from the first surface to the second surface, and
wherein the transverse thermal resistance is greater than the lateral thermal resistance.
3. The CPV device according to claim 1 ,
wherein the optical element comprises glass having a thickness in the range of 5 to 12 mm and a diameter of approximately 28 mm, and
wherein the heat spreader comprises copper having a nominal thickness of approximately 70 microns.
4. The concentrating solar collector according to claim 1 , wherein the heat spreader comprises a laminate structure including one or more non-conductive layers and one or more metallization layers.
5. The CPV device according to claim 4 ,
wherein the one or more non-conductive layers comprise a polyimide film, and
wherein the one or more metallization layers comprise one of copper or an Fe—Ni alloy.
6. The CPV device according to claim 4 , wherein the PV cell is electrically connected to one or more of the metallization layers.
7. The CPV device according to claim 1 , wherein the one or more peripheral portions comprise a plurality of radial alms extending from the central portion, wherein each adjacent pair of radial arms is separated by an associated slit.
8. The CPV device according to claim 1 ,
wherein a central region of the first side comprises a cavity, and
wherein the PV cell is disposed inside the cavity between the central portion of the heat spreader and an adjacent surface of the optical element.
9. The CPV device according to claim 8 , further comprising a transparent adhesive disposed in the cavity between the PV cell and said adjacent surface of the optical element.
10. The CPV device according to claim 1 , further comprising a primary mirror disposed between the convex surface and the peripheral portions of the heat spreader, and a secondary mirror disposed on the curved surface, wherein the primary and secondary mirrors are arranged such that light entering the optical element through the aperture surface is concentrated onto the central region of the first side, whereby the concentrated light generates heat in the central region of the first side.
11. The CPV device according to claim 10 , wherein the primary mirror and secondary mirror comprise reflective mirror films formed directly onto the convex surface and the curved surface, respectively.
12. The CPV device according to claim 11 , wherein the primary mirror and the secondary mirror comprise silver, and wherein the heat spreader comprises copper.
13. The CPV device according to claim 10 , wherein each of the primary mirror and secondary mirror comprises a reflective mirror layer, an anti-migration layer formed on the reflective mirror layer, and one or more barrier paint layers formed on the anti-migration layer.
14. The CPV device according to claim 10 , wherein the reflective mirror layer comprises silver, and wherein the anti-migration layer comprises copper.
15. The CPV device according to claim 1 , further comprising a protective shell layer disposed on a backside surface of the heat spreader.
16. A method for producing a concentrating photovoltaic (CPV) device comprising:
forming a solid, light-transparent optical element having a convex surface defining a first side, an opposing aperture surface and a curved surface defined in a central portion of the aperture surface;
forming primary and secondary mirrors on the convex surface and curved surface, respectively, thereby defining a focal region at which light received by the optical element through the aperture surface is concentrated;
forming a heat spreader by patterning a flexible flat sheet to include a central portion and multiple peripheral portions extending radially from the central portion;
mounting a photovoltaic (PV) cell directly on the central portion of the heat spreader, wherein mounting the heat spreader on the optical element comprises disposing the PV cell proximate to the first side; and
mounting the heat spreader onto the optical element such that the multiple peripheral portions are in contact with and conformally disposed over the primary mirror disposed on the convex surface such that heat generated at the focal region is passively transmitted from the heat spreader through the primary mirror and the optical element for radiation from the substantially flat aperture surface.
17. The method of claim 16 , wherein patterning the flexible flat sheet comprising patterning a flat sheet of copper.