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'Solar energy is a renewable energy which, as indicated by its name, works thanks to the Sun.
The Sun is the siege of reactions from nuclear fusions. The primary reaction lets out 1 million times more energy than a usual chemical combustion reaction. The temperature on the surface of the sun is 5880 K. The Sun rays are emitted in a spheric shape, which implies the planet that receives them will get the inverse value of the square of its distance to the Sun (Earth-Sun (average) : 92957130.358705 miles). The solar flux at the top of the Earth's atmosphere is 1320W/yd2. A large part of that energy is lost while it penetrates the atmosphere.
In 45 minutes, the Earth gets the same amount of energy as that of man's globalannual consumption (1/10000 factor). Every year, each square mile of the Sonora desert in Mexico (or of the Sahara) receives the equivalent of 2 millions of barrels of oil. The Sun provides the Earth with an energy flux that is tremendously huge and unlimited by human time scale. Photosynthetic organisms have benefited from this energy for billions of years, converting it into chemical energy (sugar, proteins, lipids), they are at the heart of all ecosystems under the sea as well as on continents.
 History of solar energy
- Socrates (470-399 BC.), a Greek philosopher who, among other things, taught bioclimactic building techniques.
- When Syracuse was besieged by the Roman fleet, in 212 BC. during the second Punic war, it is believed Archimedes (en 287-212 av JC) invented a means to set the ennemy's ships on fire by concentrating the Sun's rays using mirrors.
- Antoine Becquerel (1788-1878) invented photovoltaic battery in 1839.
- Antoine Laurent de Lavoisier (1743-1794), a chemist, invented a solar oven using convex lenses convergentes to melt metal without fuel pollution.
- Horace Bénédicte de Saussure (1740-1799), a Swiss physician, invented the "hot box" in 1767 to prove the existence of greenhouse effect. He is considered as the precursor of the flat solar captor.
- Charles Vernon Boys (1855-1944), an English physician, invented a cylindric-parabolical captor that was first activated in 1912.
- Félix Trombe (1906-1985), a French chemist had solar ovens built at Mount Louis and Odeillo in the Pyrenees to use them for the CNRS (French National Center for Scientific Research) . He developed passive heating systems such as the "Trombe wall".
 Solar technologies
There are three main ways of using solar energy : thermodynamics, thermics and photovoltaics.
- Solar power using Concentrated Thermal Power is the concentration of solar energy to produce steam and power a turbine (to produce electricity) and/or heat for desalinisation or for the industry. There are several types of trapping systems : CLFR, parabolic mittors, systems with a central tower, etc.
- Solar thermic power : used to heat water in houses (boiler or SWH), for central heating (Combined Solar System) or to cook food (Solar oven for cooking) etc. For instance, a solar boiler warms the water thanks to a pipe that runs through the solar panel. Two systems are available : flat captors (the fluid flows under the glass along a solenoid) they are cheap, but will work only in Summer. Vacuum tube collectors ( fluid that carries heat flows within a double vacuum tube). Vacuum being the best insulator, these can work in Winter as well, but they'tr much more expensive.
- Concentrated PhotoVoltaïcs concentrate solar energy thanks to optics (mirrors) towards photovoltaic cells (electricity production). A photovoltaic panel (frequently called solar panel) transforms solar energy into electricity.
- Concentration solar power / the Stirling engine : concentrates solar energy towards a Stirling engine coupled to an alternator, to produce electricity )
- Solar chimney plants : greenhouses are set on the ground and warm the air that will power turbines installed in a big chimney.
It is possible to reach very high temperatures with concentrated solar energy (9000°F or above) and can be used to purify silicium through evaporation (to obtain photovoltaic quality silicium) or for the thermolysis of water (to obtain obtention dihydrogen).
It's quite easy to trap solar energy without damaging a house (except for classified buildings) since the roof's pitch often coresponds to what's needed (about 45° for Central l'Europe). People's houses are not the only buildings that can benefit from this renewable energy resource : the cells can be set on balconies or windowsills.
 Other use of solar energy
The other most important use of solar energy is the process of photosynthesis to produce vegetable plants, (among which trees), as they create and enrich the soil (organic matter, humus, decomposition....), this arable layer is what enables the farmer to grow food. Thus solar energy is essential to feed man!
 See also
- History :
- See at Ausra
- Maps of solar radiation :