photovoltaic cell or solar cell, SEMICONDUCTOR diode that converts light to electric current. When light strikes the exposed active surface, it knocks electrons loose from their sites in the crystal. Some of the electrons have sufficient energy to cross the DIODE junction and pass through an external circuit. Because the current and voltage obtained from these devices are small, they are usually connected in large series-parallel arrays. Practical photovoltaic cells are currently about 10 to 15% efficient. Although cells constructed from indium phosphide and gallium arsenide are, in principle, more efficient, silicon-based cells are generally less costly. Solar cells have long been used to provide electric power for spacecraft. As costs have decreased, they have seen greater use as energy sources for irrigation pumps in remote areas, oil drilling platforms, and mountaintop microwave relay stations, and for small devices such as hand-held CALCULATORS.
"Photovoltaic power. Appreciation of photovoltaic power is part of the shift toward an appreciation of the elegance of the solid state that plants possess. Plants practice photosynthetic solutions to the problems of power acquisition. Compared to the water or animal-turned wheels, which are the Ur-metaphors for power production in the human world, the solid-state quantum-molecular miracle that involves dropping a photon of sunlight into a molecular device that will kick out an electron capable of energetically participating in the life of a cell seems like extravagant science fiction. Yet this is, in fact, the principle upon which photosynthesis operates. While the first solid-state devices arrived on the human cultural frontier in the late 1940's, solid-state engineering had been the preferred design approach of plants for some two thousand million years. High efficiency photovoltaics could today meet the daily needs of most people for electricity. It is the running of basic industries on solar energy that has proved difficult. Perhaps this is nature's way of telling us that we aspire to too much manufacturing."
- Terence McKenna - _Archaic Revival_