Concentrator photovoltaics

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Concentrator photovoltaics (CPV) is a term used when sunlight is concentrated onto photovoltaic surfaces for the purpose of electrical power production. Solar concentrators of all varieties may be used for this, often mounted on a solar tracker in order to keep the focal point upon the cell as the sun moves across the sky.

Compared to conventional flat panel solar cells, CPV is advantageous because the solar collector is less expensive than an equivalent area of solar cells. CPV system hardware is typically priced around 3 USD/Watt, whereas silicon flat panels are commonly 5 USD/Watt (not including any associated power systems or installation charges). Semiconductor properties allow solar cells to operate more efficiently in concentrated light, as long as the cell junction temperature is kept cool by a suitable heat sinks. CPV operates most effectively in sunny weather, since clouds and overcast conditions create diffuse light which essentially can not be concentrated.

1 Low concentration CPV
2 Medium concentration CPV
3 High concentration CPV
4 See also
5 References
6 External links

[edit] Low concentration CPV

Low concentration CPV are systems with a solar concentration 2-10 suns. For economic reasons, conventional silicon solar cells are typically used, and at these concentrations, the heat flux is low enough that the cells do not need to be actively cooled. The laws of optics dictate that a solar collector with a low concentration ratio can have a high acceptance angle, and thus does not require active solar tracking.

[edit] Medium concentration CPV

From concentrations of 10 to 100, the CPV systems require solar tracking and cooling, making them more complex.

[edit] High concentration CPV

These systems have concentrating optics consisting of dish reflectors or fresnel lenses that concentrate sunlight to intensities of 200 suns or more. The solar cells require high-capacity heat sinks to avoid thermal destruction, and to manage temperature related performance losses. Multijunction solar cells are currently favored over silicon, as they have a higher efficiency. The efficiency of both cell types rises with increased concentration; the multijunction efficiency also rises faster. Multijunction solar cells, originally designed for non-concentrating space-based satellites, have been re-designed due to the high current density encountered in CPV (typically 8 A/cm² at 500 suns). Though the cost of multijunction solar cells is roughly 100x that of a comparable silicon cell, the cell cost remains a small fraction of the cost of the overall concentrating PV system, so the system economics may still favor the multijunction cells.

Much of the original research into multijunction photovoltaics was sponsored by governments and the astronautics industry. More recently, the technical research and product development of CPV systems has grown due to investment in terrestrial electric generating systems. Recent technological advances in triple-junction solar cells by Spectrolab have yielded 40.7% conversion efficiency.^[1]

In May 2008, IBM demonstrated a prototype CPV using computer chip cooling techniques to achieve an energy density of 2300 suns.^[2]