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» Economics » Electricity » Topics begins with F » Fotovoltaik

Page modified: Wednesday, July 13, 2011 11:58:27

By Fotovoltaik (also Photovoltaik) one understands the transformation about radiation energy, primarily solar power, into electricity. It is since 1958 first in the power supply of satellites by means of solar cells in the use. Meanwhile it is used for generation of current in the whole world and applies to roof areas, with park illusory automats, at or on open spaces.

The name consists of the components photos - the Greek word for light - and Volta - after Alessandro Volta, a pioneer of the electricity -.

Technical description

The quantity of solar power, hitting as light on earth, is 10,000 times higher than the primary energy consumption (conditions 1998, 402 EJ) of mankind. The energy entry by the sun amounts to per year about 1.1 1018 KW/H. This radiation energy can be converted fotovoltaisch directly into electricity, without by-products develop such as exhaust gases (for example carbon dioxide). That wavelength coverage of the hitting and changeable electromagnetic radiation is not enough from the short-wave, visible ultraviolet (UV) over the visible range (light) until far into the longer-wave infrared range (radiant heat) inside. During the transformation the photoelectric effect is used.

The energy transformation takes place by solar cells, which are connected too for solar modules so mentioned, in Fotovoltaikanlagen. The produced electricity can be used either locally, stored into accumulators or fed into electricity mains.

In the case of feed of the energy into public electricity mains DC voltage produced by the solar cells is converted from an inverter into alternating voltage.

Every now and then an exclusive power supply is realized by means of Fotovoltaik in island systems. In order to have continuously energy here available, the energy must be stored. Acquaintance, accumulator-buffered island systems are parking meter systems, which are frequent in larger cities.

The fotovoltaische energy transformation is clearly more expensive because of the manufacturing costs of the solar modules compared with conventional power stations, whereby however large parts of the subsequent costs of the conventional energy transformation do not enter today's energy prices also. The strongly varying radiation offer makes the employment more difficult of the Fotovoltaik. The radiation energy varies foreseeable daily and seasonally conditionally, as well as daily dependent on the weather conditions. For example a firmly installed solar plant can bring one in Germany in July in relation to December up to five times higher yield. The fotovoltaische energy transformation is meaningfully applicable as a component in one energy-mixes different energy processes of change. Without the possibility of an economic energy storage generally speaking here conventional power stations will have not complete to replace yardstick. However the current feeding law and in particular the renewable energy law led to a boom with the establishment of Fotovoltaikanlagen in Germany. Thus at the end of of June 2005 the threshold was exceeded of electrical achievement installed by 1000 MW by Fotovoltaikanlagen, corresponds to a large conventional power station and means an increasing a hundredfold in the last 10 years.


The rated output in the Fotovoltaik is indicated in Wp (Watt peak) and/or kWp. "peak" (English maximum value, point) refers to the achievement with test conditions, which do not correspond to the everyday life enterprise directly. It does not act thereby also around the achievement of the cell or the module during highest sun exposure. The test conditions serve for the standardisation and for the comparison of different solar cells or - modules. The electrical values of the construction units under these conditions are indicated in the data sheets. With 25 "°C module temperature, 1000 W/m are measured irradiancy and an air measure of 1,5. These are the STC conditions (standard test conditions), which as international standard was specified. If these conditions cannot be kept with testing, then the rated output must be determined computationally from the given test conditions. The irradiancy of 1000 W/m does not come into Central Europe over one year seen very frequently forwards (the further south, the more frequently). In the normal enterprise solar modules and/or the solar cells have a substantially higher operating temperature than the 25 "°C and concomitantly a clearly lower efficiency planned in the test when this irradiation.

The middle annual production of a again in each case established net-coupled Photovoltaik plant in Germany, which can be expected, rises for years with improvement of the technology continuously and lies at present during meaningful interpretation of the plant at values around 900-1000 kilowatt-hours per kWp (source: Fraunhofer Institut for solar energy systems ISE, 2006).


With solar cells in the Fotovoltaik obtained efficiency reach from little per cent (for example about 6 per cent for cadmium tellurium ID solar modules) up to over 35 per cent (concentrator multi-layer laboratory copy). The efficiencies of usual market solar modules lie between 10 and 16 per cent. For general survey however still the losses of the inverter flow also.

Although the sun exposure altogether the available appears immensely high, the Fotovoltaik is very surface intensive due to at present rather low efficiency. Thus a wind-powered device with 5 MW achievement produces about exactly the same much energy like 500 m X.500 m (25 hectars) a large solar electricity plant.


The attainable Potenzial is very high: Despite the apparently unfavorable conditions in Germany were sufficient theoretically about 2 per cent for the total area of the country, in order to harvest with today available technology in the yearly total the same electricity, Germany altogether per year necessarily. The objection, the surface in Central Europe would be sufficient for a substantial portion from Fotovoltaik to the power supply, is not thus not durable. The necessary surface could be achieved without new sealing by means of the use of cultivated surfaces (above all roofs). The Fotovoltaik can on a long-term basis supply therefore also to Germany a substantial contribution to the climatic protection and to the preservation of resources.

The number mentioned of 2 % results in the case of an installed achievement of one kWp per 10 m surface, an annual energy yield of approx. 750 KW/H per kWp, requirements of electric current of Germany of approx. 550 billion a KW/H (the order of magnitude for the year 2004 and 2005) and the total area of Germany of approx. 350,000 km

In the year 2005 approx. 0.2 per cent of the German generation of current from solar energy were won, however with constantly strong growth, which corresponds for instance to an increasing tenfold of the production every five years. For the year 2010 different prognoses go from 0,45-1,0 per cent (source: Federation of the network carriers/Federal association renewable energies). Also with theoretically high Potenzialen solar electricity plays up-to-date and in the next years for the German generation of current only a very small role, however the current portion from Fotovoltaik for a functioning regenerativ is energy-mixes necessarily by the offer behavior of the solar power moving in opposite directions to the wind.

With the above data to area requirements a possibly necessary intermediate storage of the energy is not yet considered. If one assumes 25 % of the energy are used immediately and 75 % are stored would double, this with transformation losses of 50 % area requirements for Fotovoltaik approximately and would require additional capital outlays.

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