History

• Solar energy use dates back as far as the Greeks and Romans. They designed their homes to face south to help capture the heat generated by the sun. This is called passive solar energy, which is used without significant technological intervention. The real advance came when the first solar cell was developed at Bell Labs in 1953, according to southface.org. Since then solar technology has advanced slowly, hindered by cheap petroleum, but a surge in demand since the 1990s has made it more economical.
  
  

Passive Thermal

• Passive thermal techniques are still in use today. Many homes are placed to maximize southern exposure and some have special walls designed to capture heat. Passive thermal systems are also used to heat water; a solar collector holds water heated by the sun. The water is generally moved by gravity rather than an electric pump.
  
  

Active Thermal

• Active thermal systems are more complex and typically employ pumps and special thermal collectors. The simplest and most frequently used is called a flat plate collector. These are shallow boxes with copper pipes embedded in insulation that is normally painted black and covered with a sheet of dark glass. A fluid, water or antifreeze, is passed through the piping and heated by the captured thermal energy and then routed into a hot water heater. Similar systems can also distribute heat in a home or building.
  
  

Solar Electricity

• Solar electricity for residential and commercial use is generated using photovoltaic cells. In essence, when photons, or light, strike the cells, it causes electrons to move. These moving electrons are caught by wires that run throughout the cell and transferred out of the cell. The wires carry the electrons to an inverter that converts the direct current from the cells into alternating current that can be used in the home or fed into an electrical grid.
  
  

Solar Power Plants

• Solar power plants use different methods to produce electricity. One method is a linear concentrator system, which uses curved mirrors to concentrate sunlight onto fluid-filled tubes. The heated fluid is used to boil water that turns a steam turbine. A second method involves using a large dish to concentrate sunlight onto a receiver. The receiver heats liquid to move engine parts that run generators. A third system is called a power tower that has numerous mirrors to focus light onto a receiver that uses the concentrated energy to generate steam for a turbine system.