Micro concentrator photovoltaics (micro-CPV) is an unconventional approach for developing high-efficiency low-cost PV systems. The micrifying of cells and optics brings about an increase of efficiency with respect to classical CPV, at the expense of some fundamental challenges at mass production. The large costs linked to miniaturization under conventional serial-assembly processes raise the need for the development of parallel manufacturing technologies. In return, the tiny sizes involved allows exploring unconventional optical architectures or revisiting conventional concepts that were typically discarded because of large material consumption or high bulk absorption at classical CPV sizes. FIGURE 1. Panasonic micro-CPV prototype with dimensions and a layout scheme. [11] -Reproduced with permission
The Swiss start-up Insolight aims to be the first company to commercialize a high-efficiency III-V based low profile micro-CPV product that uses planar micro-tracking to eliminate the need for a tilting solar tracker, allowing rooftop mounting using typical flat-plate hardware, as well diffuse light capture using low cost Si solar cells which cover the area of the back plane not taken up by III-V solar cells. The IES-UPM has made an initial performance evaluation of a 0.1m2 prototype. We show that the integrated planar tracking can reach 55° AOI, show CSTC efficiency near to 30% for III-V output, and demonstrate the diffuse capture and planar tracking capability in a multi-week test campaign at our test site in Madrid. Index Terms-integrated planar tracking, diffuse light collection, micro-concentrator photovoltaics.
A tracking-integrated hybrid micro-concentrator module is presented that can harvest direct, diffuse, and albedo irradiance components. It uses biconvex 180× lens arrays to concentrate direct light on high-efficiency III-V solar cells (29% module efficiency has been demonstrated outdoors on direct sunlight at Concentrator Standard Test Conditions) and a planar micro-tracking mechanism to allow installation in static frames. Two architectures have been developed to harvest diffuse irradiance: (1) a hybrid architecture where the backplane is covered with monofacial or bifacial Si cells; (2) a translucent architecture where diffuse light is transmitted through the module for dual-land-use applications, such as agrivoltaics. Simulations show that the hybrid architecture provides an excess of yearly energy production compared to 20% efficiency flat-plate photovoltaic (PV) module in all locations studied, including those with a low direct normal irradiance (DNI) content, and up to 38% advantage in high-DNI locations. The use of bifacial heterojunction and interdigitated back-contact Si cells has been explored for the glass-Si-glass backplane laminate to harvest albedo light. Bifacial gains modeled can boost energy yield by about 30% in the best scenario. We discuss the perspectives of the translucent modules for dual-land-use applications as well, such as integration in greenhouses for agriculture-integrated PV (agrivoltaics). This architecture can provide up to 47% excess electricity compared to a spaced reference Si array that transmits the same amount of solar
Roll-to-roll nanoimprint lithography (R2R-NIL) is an enabling technology for the low-cost mass production of high-quality micro- and nano-sized optical elements. Particularly, the fabrication of Fresnel lenses using R2R-NIL is a promising approach to produce optical arrays for micro-concentrator photovoltaic modules. This work investigates the application of a continuous R2R imprinting process based on ultraviolet curing of transparent photopolymer resins (UV-NIL) to fabricate high-efficiency and low-cost Fresnel lenses. The morphological attributes and the related optical performance of the lenses fabricated using roll-to-roll UV-NIL on flexible PET sheets yielded optical efficiency values up to ∼ 69% at a concentration ratio of 178X, whereas a value of ∼ 77% was obtained for the UV-NIL batch processed on a flat rigid substrate. Further improvement of the optical efficiency has been achieved by adding moth-eye inspired antireflective (AR) features on the side opposite to the Fresnel motifs via a double-sided R2R UV-NIL process. The process developed paves the way for cost-effective mass production of high-efficiency Fresnel lenses for micro-concentrator photovoltaics.
The open circuit voltage of a single subcell in a multijunction cell stack can be measured with the help of pulsed, millisecond illumination. This concept makes use of the fact that the charging of the non-illuminated cell capacitances takes place on a much longer timescale than of the illuminated one. Optical coupling introduces a photocurrent in the subcell underneath. Its efficiency can be quantified in parallel under short circuit conditions. A suns-Voc approach, applied to this subcell pair, yields all relevant diode parameters. Applied to all subcells of a Ga0.50In0.50P/Ga0.99In0.01As/Ge triple junction cell, a very good match to the dark I-V curve is obtained
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