Photovoltaic | ThermalUnique Energy harnesses solar power using the two methods most proven effective today: Photovoltaics and CSP (Concentrated Solar Power) or Thermal Energy.
In this method of solar power generation, solar radiation is converted to direct current electricity using photovoltaic semi conductors. This involves the use of solar panels that are made up of cells containing photovoltaic material. Some leading photovoltaic materials include Monocrystalline Silicon, polycrystalline silicon, amorphous silicon, cadmium telluride, and copper indium selenide/sulfide.
Upon exposure to light, in this case sunlight, the photovoltaic material creates voltage. Unlike the photo electric effect, where electrons are ejected from a material, in the Photovoltaic effect, electrons are transferred between different bands within the same material, generating a build up of voltage between two electrodes.
The photovoltaic effect was first observed as far back as 1939 by Alexandre-Edmonde Becquerel. It was first used to generate energy by the Vanguard I satellite in 1958, which continued to transmit after its regular battery had run out. In subsequent decades, it grew to be an essential component of satellite technology and was widely used in telecommunications. It was the 1973 oil crises which gave impetus to the growth of PV use. Today, prices have dropped and technology improved sufficiently to make PV viable for more applications. Solar photovoltaics now generates electricity in more than 100 countries but this is still a tiny fraction of the 15 TW total global power-generating capacity from all sources.
Concentrated Solar Thermal Systems or Concentrated Solar Power
Thermal Solar Energy or Concentrated Solar Power (CSP) uses mirrors or lenses to concentrate the sun's radiation to produce heat, which is then used to power a turbine that produces electricity. This is based on much the same principle that sets fire to a scrap of paper held under a magnifying glass angled to capture the sun's rays. The higher the efficiency of the concentrating device, the smaller the plant size, the lesser the land used and the lower the environmental impact and expense. The energy generated from the concentrating device is used to run steam or gas turbines. The advantage of the thermal method is that heat is stored. This stored heat can be used for generation of electricity at night. Heat in a CSP includes 5 processes - heat gain, heat transfer, heat storage, heat transport and heat insulation. There are various designs of reflectors, including parabolic troughs, power towers, dish stirlings, Fresnel reflectors etc. A recent study has shown that by 2050, CSP could account for 25% of the world's energy needs.
The use of reflectors to harness the sun's energy can be traced back centuries. But the first major breakthrough can be considered to be Auguste Mouchout' steam solar engine, produced in 1866 using steam produced from a parabolic trough. The first patent for a Solar Collector was obtained by the Italian Alessandro Battaglia in Genoa, Italy, in 1886. Over the following years, inventors such as John Ericsson and Frank Shuman developed concentrating solar-powered devices for irrigation, refrigeration, and locomotion. The first Solar Concentrated plant was opened in Genoa near Italy in 1968, by Professor Giovanni Francia. This plant was the precursor of today's solar concentrated plants with a solar receiver in the center of a field of solar collectors. This was followed in 1981 by 10 MW Solar One power tower in Southern California and a parabolic trough plant Solar Energy Generating Systems (SEGS), in 1984. The 354 MW SEGS is still the largest solar power plant in the world.