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CPV Concentration Photovoltaics

Concentration Photovoltaic technology (CPV) uses an optical system to concentrate light onto a solar cell, so that the area of semiconductor that forms the cell can be reduced, allowing for more complex, expensive and higher efficiency solar cells. These high efficiencies can compensate the higher operation temperatures and the need of trackers to collect the direct irradiance, making the CPV system cost competitive: the price estimates for CPV electricity are in the range of those for Concentrated Solar Power and flat-plate PV technology in areas with high direct irradiance [Philipps].

CPV was proposed several decades ago mainly based on high-efficiency silicon solar cells, but the electricity prices of those systems were not competitive enough. A new stage of development has been reached in the last decade thanks to the progress in multijunction (MJ) solar cells, which reach efficiencies much higher than those of single junction silicon solar cells: up to 44.4% for a 3-junction solar cell [Sasaki] and 46% for a 4-junction one [Dimroth]. CPV modules have reached efficiencies over 35% [Philipps], and there are CPV plants already built some years ago demonstrating operation without significant degradation and with high availability [Gerstmaier].

CPV systems can be classified depending on the concentration level in low (2-100 suns, where “sun” means the ratio of the areas of the receiving surface and the solar cell), medium (100-300 suns) and high (300-1000 suns) concentration systems. Luminescent concentrators are a kind of low concentration systems in which the concentration comes from fluorescent species. The higher the level of concentration, the higher the requirements in terms of cooling (which for the highest concentration levels may need to be active) and sun tracking (which is not needed for the very low concentration levels, and has to be 2-axis tracking for medium and high concentration systems).

A wide variety of systems with different concentration levels and optical designs, based on both lenses and mirrors, have been proposed and developed throughout the last twenty five years [Luque] [Sala]. The existence of such a wide variety of concepts currently under development shows that no single architecture has yet emerged as the most cost competitive. However, concentrators based in Fresnel lenses are the most popular ones nowadays.

The scenario for research on CPV should share two lines of work: from one side the development of potentially very efficient solar cells; and from the other side improving the optics, receivers, cooling, housing and tracking subsystems toward few optimal solutions of proven reliability and manufacturability.

Edited by Carlos del Cañizo

References

[1] Dimroth, M. Grave, P. Beutel, U. Fiedeler, C. Karcher, T. N. D. Tibbits, E. Oliva, G. Siefer, M. Schachtner, A. Wekkeli, A. W. Bett, R. Krause, M. Piccin, N. Blanc, C. Drazek, E. Guiot, B. Ghyselen, T. Salvetat, A. Tauzin, T. Signamarcheix, A. Dobrich, T. Hannappel, and K. Schwarzburg, “Wafer bonded four-junction GaInP/GaAs//GaInAsP/GaInAs concentrator solar cells with 44.7% efficiency,” Prog. Photovolt. Res. Appl., vol. 22, no. 3, pp. 277–282, Mar. 2014
[1] Gerstmaier, T. Zech, M. Röttger, C. Braun, and A. Gombert, “Large-scale and long-term CPV power plant field results,” AIP Conference Proceedings, vol. 1679, p. 030002, 28-Sep-2015.
Luque. Solar cells and optics for photovoltaic concentration. A. Hilger, 1989
Philipps, A. W. Bett, K. Horowitz, and S. Kurtz, “Current status of Concentrator Photovoltaic (CPV) Technology,” NREL, Fraunhofer-ISE, 2015.
Sala, I. Antón, Photovoltaic Concentrators, Chp 10 in Handbook of Photovoltaic Science and Engineering, Edited by A. Luque and S. Hegedus, John Wiley & Sons, 2011, pp. 402-451
Sasaki, T. Agui, K. Nakaido, N. Takahashi, R. Onitsuka, and T. Takamoto, “Development of InGaP/GaAs/InGaAs inverted triple junction concentrator solar cells,” AIP Conference Proceedings, vol. 1556, pp. 22–25, 2013