Photovoltaics Generally speaking, photovoltaic solar cells use a semiconductor material that is exposed to sunlight. The energy of the incident light displaces electrons from their normal atomic orbits and an electrode grid structure on the surface of the semiconductor collects these electrons and makes them available for use in an external circuit. This is very similar to the way that the chemical reaction and the electrodes in a dry battery cell make electrons available for external use. The terms crystalline, thin film and concentrator describe the manner in which the semi-conducting material is processed and optimized as a photovoltaic cell. Crystalline cells are fabricated from ingots of the semiconductor material, usually silicon, that are cut into relatively thin slices, processed to optimize the electron collection efficiency and laminated into a protective enclosure.
All types have their merits and problems and are described in detail in the referenced locations.
The fluid is then pumped into a steam generator where the heat is transferred to water turn it into steam. The steam can then be used to spin a conventional steam turbine connected to a generator to make electricity. In the case of the trough, the mirror is a long parabola with a steel tube containing the heat transfer fluid running along the focal axis of the mirror. The axis of the mirror is usually aligned in a North-South direction and the mirror is rotated from East to West as the day progresses so that the energy from the sun is continually focused onto the steel tube. The power tower system is a little different in that all of the transfer fluid heating is achieved in a heat receiver on the top of a tower located in the center of a field of computer controlled mirrors, or heliostats.