Photovoltaics
conversion of sunlight into electricity, (also called solar cells). Flat thin cells of a semiconductor made from silicon create an electrical charge when exposed to light. Utilized by tapping opposit surfaces of the cell with small wires.
Equivalent to DC current. Often converted to AC with a "synchronous inverter". AC can be sold back to the utility company.
Cells = Early cells were made of crystalline silicon.
Common now is amorphous silicon cell.
Efficiencies range from 10-13%, 60% has been attained in laboratory tests.
Wind turbines
Similar in function to a windmill. Generate electricity through a generator or alternator.
Average windspeed of 10mph or more is required. 13mph average results in a steady profit.
Vertical axis wind turbine (VAWT) =
Savonious - composed of two offset cups that spill into each other, like two halves of a steel drum sliced, slid halfway apart and mounted on a vertical pole.
Darrieus - resembles a single eggbeater stuck in the ground.
Both types work regardless of wind direction. Savonious is not as efficient but self starting. Darrieus is very efficient but will nt start itself but picks up speed once going.
Horizontal axis wind turbine (HAWT)
More common than VAWT's
Giant fan blade perpendicular to the ground mounted to horizontal body attached to a tower.
leading blade = blades upwind of the tower, requires a tail, like a weather vane or sensors and motors to keep in direction of wind
trailing blade = blades downwind of the tower, results in eccentric vibration due to the "wind shadow" of the tower.
time: 0.5, 7:40-8:10pm 6/16/09
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