Photovoltaic energy

Photovoltaic energy is the conversion of sunlight into electricity. A photovoltaic cell, commonly called a solar cell or PV, is the technology used to convert solar en­ergy directly into electrical power. A pho­tovoltaic cell is a non-mechanical device usually made from silicon alloys.
Sunlight is composed of photons, or particles of solar energy. These photons contain various amounts of energy corre­sponding to the different wavelengths of the solar spectrum. When photons strike a photovoltaic cell, they may be reflected,pass right through, or be ab­sorbed. Only the absorbed photons provide energy to generate electricity. When enough sunlight (energy) is absorbed by the material (a semiconductor), electrons are dislodged from the material's atoms. Special treatment of the material surface during manufacturing makes the front surface of the cell more receptive to free electrons, so the electrons naturally mi­grate to the surface.
When the electrons leave their position, holes are formed. When many electrons each carrying a negative charge , travel toward the front surface of the cell, the resulting imbalance of charge between the cell's front and back surfaces creates a volt­age potential like the nega­tive and positive terminals of a battery. When the two surfaces are connected throughan external load, electricityflows.Some advantages of photovoltaic systems are:

1. Conversion from sunlight to electricity is direct, so that bulky mechanical gen­erator systems are unnecessary.

2. PV arrays can be installed quickly and in any size required or allowed.
3. The environmental impact is minimal,requiring no water for system cooling and generating no by-products.Photovoltaic cells, like batteries, gen­erate direct current (Dc) which is gener­ally used for small loads (electronic equip­ment). When DC from photovoltaic cells is used for commercial applications or sold to electric utilities using the electric grid, it must be converted to alternating current (AC) using invert­ers, solid state devices that convert DC power to AC.
Historically, PV has been used at remote sites to provide electricity. In the future PV arrays may be locat­ed at sites that are also connected to the electric grid enhfncing the reli­ability of the distribution system.

Solar thermal heat

Solar thermal (heat) energy is often used for heating swimming pools, heating water used in homes, and space heating of buildings. Solar space heating systems can be classi­fied as passive or active.
Passive space heating is what happens to your car on a hot sum­mer day. In buildings, the air is cir­culated past a solar heat surface(s) and through the building by convec­tion (i.e. less dense warm air tends to rise while more dense cooler air moves downward). No mechanical equipment is needed for passive so­lar heating.
Active heating systems require a collec­tor to absorb and collect solar radiation. Fans or pumps are used to circulate the heated air or heat absorbing fluid. Active systems often include some type of ener­gy storage system.