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Photovoltaic solar panels |
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The photovoltaic (sometimes called photoelectric) effect, or the conversion of light into electricity, was discovered by Becquerel in 1839,but it did not find an industrial application until 1954, when it was used in the space sector.
How does it work? Photons (“light particles”) are capable of nudging peripheral electrons of certain atoms of semi-conducting elements out of position. Thus an electric current is produced (an electric current is simply a displacement of electrons). Most photovoltaic captors use the properties of silicon, an element providing good
yields in this type of application. It is also abundant in nature. Yields vary from 5 to 16% depending on the type of silicon crystallisation (10 to 16% for polycrystalline silicon, 5 to 10% for amorphous silicon), the more efficient cells being the most expensive to manufacture. Research is continuing in an attempt to improve yields.
A photovoltaic captor is a panel into which the photovoltaic cells are integrated. The desired power and exit voltage (12, 24, 48 V …) is obtained by arranging the cells in the panel in particular ways. The output is a direct current. A DC/AC converter is used to transform the direct current into alternating current enabling it to be fed into the electricity network or directly into the majority of modern electric appliances). The power output of most of the panels in use is between 50 and 200
W (watts). The power of a photovoltaic array varies with the amount of sunshine it receives. The watt represents the power supplied in standard reference conditions: sunlight of 1000 W/m² at a temperature of 25°C).
The cells are fragile: for this reason they are encapsulated in solar panels in order to protect them from shocks and humidity. |
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| Photovoltaic captors. |
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Photovoltaic electricity has several applications:
- Supplying electricity to isolated dwellings and other sites that are located a long way from the electricity network (rural zones in developing countries, communication relays, motorway telephones, marine beacons, satellites …), uses which represent 25 to 30% of the market;
- Systems connected to the electricity network (photovoltaic roofs and walls in houses, photovoltaic electricity power plants), representing 70 to 75% of the market;
- Other individual applications such as watches and hand calculators that use low power cells, accounting for 2 to 5% of the market.
Investment in the production of photovoltaic electricity is expensive. It needs to be stimulated by a significant system of grants and aid. In France for example, a law was voted in February 2000 providing aid in the form of an obligation on the EDF (French electricity supply company) to purchase photovoltaic electricity at a higher-than-normal tariff. This assistance applies to all small production units (less than 12 MW) of renewable energy, but it is photovoltaic electricity that is purchased at the highest tariff (0.15 euros/kWh compared, for example, to 0.08 euros/kWh for wind energy). In Germany, the repurchase price of photovoltaic electricity is 0.6 euros/kWh.
There is also assistance in the form of fiscal advantages: thus, since January 2005, French people who decide to install a photovoltaic system are eligible for a tax credit of 40% of the equipment cost. |
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