Solar energy is energy from the Sun. This energy drives the climate and weather and supports virtually all life on Earth. Heat and light from the sun, along with solar-based resources such as wind and wave power, hydroelectricity and biomass, account for over 99.9 percent of the available flow of renewable energy.
Solar energy technologies harness the sun's energy for practical ends. These technologies date from the time of the early Greeks, Native Americans and Chinese, who warmed their buildings by orienting them toward the sun. Modern solar technologies provide heating, lighting, electricity and even flight.
Solar power is used synonymously with solar energy or more specifically to refer to the conversion of sunlight into electricity. This can be done either through the photovoltaic effect or by heating a transfer fluid to produce steam to run a generator.Earth receives 174 petawatts of incoming solar radiation (insolation) at the upper atmosphere at any given time. When it meets the atmosphere, 6 percent of the insolation is reflected and 16 percent is absorbed. Average atmospheric conditions (clouds, dust, pollutants) further reduce insolation traveling through the atmosphere by 20 percent due to reflection and 3 percent via absorption. These atmospheric conditions not only reduce the quantity of energy reaching the Earth's surface, but also diffuse approximately 20 percent of the incoming light and filter portions of its spectrum.[3] After passing through the Earth's atmosphere, approximately half the insolation is in the visible electromagnetic spectrum with the other half mostly in the infrared spectrum (a small part is ultraviolet radiation).[4]
Solar photovoltaics provide 0.04% of the world's energy usage.
Wind Energy
Wind power is the conversion of wind energy into useful form, such as electricity, using wind turbines. At the end of 2006, worldwide capacity of wind-powered generators was 73.9 gigawatts; although it currently produces just over 1% of world-wide electricity use,[1] it accounts for approximately 20% of electricity production in Denmark, 9% in Spain, and 7% in Germany.[2] Globally, wind power generation more than quadrupled between 2000 and 2006.[3]
Most modern wind power is generated in the form of electricity by converting the rotation of turbine blades into electrical current by means of an electrical generator. In windmills (a much older technology), wind energy is used to turn mechanical machinery to do physical work, such as crushing grain or pumping water.
Wind power is used in large scale wind farms for national electrical grids as well as in small individual turbines for providing electricity to rural residences or grid-isolated locations.
Wind energy is plentiful, renewable, widely distributed, clean, and reduces toxic atmospheric and greenhouse gas emissions if used to replace fossil-fuel-derived electricity. The intermittency of wind seldom creates insurmountable problems when using wind power to supply up to roughly 10% of total electrical demand (low to moderate penetration), but presents challenges that are not yet fully solved when wind is to be used for a larger fraction of demand.[4]
The origin of wind is complex. The Earth is unevenly heated by the sun resulting in the poles receiving less energy from the sun than the equator does. Also the dry land heats up (and cools down) more quickly than the seas do. The differential heating drives a global atmospheric convection system reaching from the Earth's surface to the stratosphere which acts as a virtual ceiling. Most of the energy stored in these wind movements can be found at high altitudes where continuous wind speeds of over 160 km/h (100 mph) occur. Eventually, the wind energy is converted through friction into diffuse heat throughout the Earth's surface and the atmosphere.
There is an estimated 72 TW of wind energy on the Earth that can potentially be converted to electricity and that is commercially viable [5].
Geothermal Energy
Geothermal power (from the Greek words geo, meaning earth, and therme, meaning heat) is energy generated by heat stored beneath the Earth's surface. Prince Piero Ginori Conti tested the first geothermal power plant on 4 July 1904, at the Larderello dry steam field in Italy.[1] The largest group of geothermal power plants in the world is located in The Geysers, a geothermal field in California.[2] As of 2007, geothermal power supplies less than 1% of the world's energy.[3]
Solar energy is energy from the Sun. This energy drives the climate and weather and supports virtually all life on Earth. Heat and light from the sun, along with solar-based resources such as wind and wave power, hydroelectricity and biomass, account for over 99.9 percent of the available flow of renewable energy.
