Photovoltaic (PV) systems use active semiconductor cells, typically silicon based, to directly convert the sun's energy into electricity. This conversion of sunlight to electricity occurs without moving parts, is silent and pollution free in its operation. The solar electricity fed through electronic equipment is converted to utility grade electricity for use directly in the home. The solar electricity can be used to offset the need for purchased utility electricity or, if the PV electricity exceeds the home's requirements, the excess electricity can be sent back to the utility, typically for credit.
High concentration photovoltaic (CPV) systems have concentrating optics consisting of dish reflectors or fresnel lenses that concentrate sunlight to intensities of 200 suns or more. Multijunction solar cells can then be used to convert sunlight into electricity. Multijunction cells typically have much higher efficiency than silicon ones and work with high current density 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 favor the CPV technology.