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Concentrator systems use lenses or reflectors to focus sunlight onto the solar cells or modules. Lenses, with concentration ratios of 10x to 500x, typically Fresnel linear-focus or point-focus lenses, are most often made of an inexpensive plastic material engineered with refracting features that direct the sunlight onto a small or narrow area of cells. The cells are usually silicon. GaAs cells and other materials would have higher conversion efficiencies, and could operate at higher temperatures, but they are often substantially more expensive. Module efficiency can range upwards from 17%, and concentrator cells have been designed with conversion efficiencies in excess of 30%. (reference #92)
Reflectors can be used to augment power output, increasing the intensity of light on modules, or to extend the time that sufficient light falls on the modules. Concentrator system lenses are unable to focus scattered light, limiting their use to areas, like desert areas, with a substantial number of cloudless days on an annual basis. (reference #18) |
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