Solar energy can be captured passively and actively. In passive solar systems, the key is to allow solar radiation to pass through a selective material, such as glass, without allowing it to re-radiate back out. This is termed thermal storage and it can be used for several applications, including space heating for the home, to produce domestic hot water, and for the heating of swimming pools and spas. A passive solar heating system harvests energy from the sun without the use of electrical or mechanical devices.
Construction techniques and architectural designs can implement these types of systems quite easily, incorporating facets such as the orientation of the home, location of windows and overhangs, types of construction materials used, and landscaping options into building plans that would be best suited for maximum solar benefits.
An active solar system uses electrical or mechanical equipment to increase solar energy extraction. Photovoltaic panels and solar thermal collectors which harness solar energy are examples of active solar technology. Most collectors incorporate the use of an energy storage system that will provide heat when the sun is not shining. The collector, absorbing solar energy, converts it into heat, which through the coolant heats buildings, heats water, can transform it into electrical energy, etc. Solar collectors can be used in all processes in industry, agriculture, household needs, where heat is used.
Photovoltaic modules are the most known types of solar energy collecting panels. Most solar cells are made from silicon, a semiconductor. It is “doped” with positive ions on one side and with negative ions on the other. When light (photons) strikes the solar cell, it knocks loosely held electrons from the negative side. These excited electrons are then attracted to the positive side of the solar cell, and if there is an electrical conductor between both sides, an electrically charged circuit is created.