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Solar Technology

In 1839 the French physicist A. Becquerel discovered the photovoltaic effect which transforms the energy from sunlight into electric current. The photovoltaic effect is obtained through the absorption of photons by  semiconducting materials : the resulting displacement of the electrons generates electric current.

The semiconducting material used today to produce PV cells is a very pure silicon. This material, despite the abundance of its raw materials (sand), demands costly and complex industrial procedures.

There are 3 main types of industrial PV cells:

  • Monocrystal cells which are first generation solar cells with a 12%-16% yield, however production is difficult and costly as a large quantity of energy is needed to obtain a pure crystal.
  • Polycrystal cells yield between 11-13% but production costs are lower.
  • Amorphous cells have lower production costs but a yield of 6-9%. This technology uses thin layers of silicon. Amorphous silicon units are made by depositing very thin layers of vaporized silicon in a vacuum onto glass, soft plastic or metal and thus creating flexible panels.

Other technologies (using several semiconducting materials, optical concentrators or organic chemistry composites) are at a developmental stage. It is highly likely thanks to large investments in the last years in research and development, that new materials will be discovered allowing a further reduction in the cost price of solar kWh, which will in turn lead to wider distribution.



The other types of cells

The type of cells which will be on the solar market are Tandem cells, multi junction  cells and semi-conducting CIGS cells which we should begin to see on the market in 2010.

1. The tandem cells

These cells are made from a thin layer of amorphous cells placed onto cyrstalline silicon. The combination of these two types of cells allows a greater light absorption and thus a better yield even with little sunlight. However the manufacturing costs are high due to the layering of the different cells.

2.The multi junction cells

These cells work under the same principle as the tandem cells. They are made up of a large number of semi-conductors(GaAs, Ge, GalnP2 ...)  each of which has a limited spectrum. A yield of 50% can be obtained when selecting materials which have similar wavelengths and thus creating the widest possible spectrum.

The drawback of these cells is however the manufacturing cost, no industrial production has been set up for the moment.

3. Semi conducting CIGS

This new technique is based on the use of a mixture of semi-conducting materials( copper, gallium, indium and selenium) instead of using the current silicon. The manufacturing procedure, as used in printing, consists in placing four consecutive layers of semi-conductors onto a soft metal strip. This procedure allows the cost of the cells and thus the PV panels to be greatly reduced, the price of a solar watt could be as little as 1 dollar