Sun
Photovoltaics, a renewable energy source for direct use or resale
09/14/2010
Of the various renewable energy sources, the electricity produced by solar photovoltaic energy can be used in two ways: either directly in the production facility or sold back to the grid. However, at current rates of costs and yield, this form of energy still requires grant aid.
© Total / Dufour Marco
Converting light into electricity
The photovoltaic (or photoelectric) effect involves converting light into electricity. It was discovered by French physicist Edmond Becquerel in 1839 and was first used in industrial applications in 1954.
The principle: an electric current occurs when photons (light particles) displace the peripheral electrons of the atoms of certain semi-conducting elements.
Light hitting the photovoltaic cell is converted into electricity by a semi-conductor (a material that allows the electric current to pass), generally silicon. A photovoltaic array is made up of several cells producing a direct current with voltage of 12, 24 or 48 volts. This direct current is then converted into alternating current by an inverter, enabling it to be transmitted over a high-voltage transmission network.
Most panels deliver power of 50-200 watt-peak (Wp). A watt-peak represents the power provided in standard reference conditions, i.e. solar radiation of 1000 W/m² and temperature of 25°C.
This form of energy provides yield of about 18% (compared to a maximum of 60% for wind energy and 33% for nuclear energy, for example).
In general, the yield of photovoltaic cells can be increased:
• Either by purifying the semi-conductor used as much as possible
• Or by stacking a number of semi-conductors one on top of another, each of which uses a slightly different light wavelength, thus improving efficiency.
However, the higher the yield, the more expensive the cell. Furthermore, a toxicity issue arises with cadmium telluride cells, which are less expensive and have higher performance than silicon.
The advantages of photovoltaics:
• It is a non-polluting energy source available in many regions. South, southeasterly or southwesterly aspects all provide satisfactory results.
• Its modular components - small size panels - blend in easily with house roofs or facades.
• It provides electricity in regions that are difficult to access with the national grid, and makes buildings self-sufficient in terms of energy.
• It is low-maintenance and its components last 20-30 years.
Varied uses... coupled with incentives
The electricity produced using photovoltaics has two main uses:
• Supplying electricity to isolated sites, including housing, public lighting, wells, maritime beacons and water pumps, accounting for 25-30% of this market worldwide.
In this case, the electricity is stored in batteries to ensure distribution outside daylight hours or as and when the need arises.
• Feeding into the national grid. This accounts for 70-75% of the photovoltaic market.
Other minor uses - such as supplying watches or calculators using low-power cells - account for 2-5% of the market.
As a clean, renewable energy source, photovoltaics is encouraged by the public authorities. The purchase price for this electricity produced and sold back to the grid is often higher than the public price. Moreover, individuals who decide to install it can avail of tax incentives (tax credits) in France.
Photovoltaic energy offers the highest purchase price for the 2010-2012 period:
- Building integrated photovoltaics: 0.58 euro/kWh for residential, educational or healthcare buildings and 0.50 euro/kWh for other buildings.
- Roof-based photovoltaics: 0.42 euro/kWh.
- Ground-based photovoltaics: 0.314 euro/kWh.
By way of comparison, the market price is 0.05-0.06 euro/kWh1
[1] Source: Légifrance, prices applicable as at January 12, 2010
