Sustainable Technologies
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Photovoltaic, Concentrated (CPV)
Photovoltaic, Concentrated (CPV)
CPV employs photovoltaic cells but rather than rely on the standard 1000 watts per square meter intensity of naturally occurring solar radiation energy, the CPV system concentrates the sunlight and directs a magnified beam of sunlight onto a smaller area solar cell that is specifically designed to handle the greater energy and heat. Because the solar cell can be much smaller, the amount of silicon or other semiconductor material required is far less for the same watt capacity output when compared to non-concentrated PV systems. This can greatly reduce the construction cost per watt capacity of the overall system. Because of the increased heat on the solar cell, CPV installations often require integration of heat sinks or other cooling apparatus. CPV can reach the greatest installed efficiencies of existing PV installations for utility scale application.

The magnification of the sunlight can be accomplished by a number of methods, the most common of which is a Fresnel lens. These systems are often set to track the sun’s movement across the sky (heliostatic, dual-axis tracking) because such Fresnel lenses only function when perpendicular to the path of light.

Other variations employ parabolic troughs that direct sunlight onto a linear solar cell. The parabolic reflecting surface requires tracking of the sun in only one axis. This is similar to the solar thermal parabolic trough in its design.

A variation on this is the Total Spectrum Collector in which separates light with a prism into different spectrums which are best suited to different solar cell types.

Still another variation is the mylar balloon design developed by Cool Earth in which a CPV solar cell at the upper side of a clear hemisphere receives concentrated sunlight from the lower hemisphere which is highly reflective on the inside surface. This system is also sun-tracking.