What is thermosolar power or concentrating solar power (CSP)?

What is thermosolar power, concentrating solar power or "desert energy"?

Thermosolar energy means generating electricity from the heat of the sun, and not, as photovoltaic panels do, from sunlight. Since a large quantity of solar heat is required, evidently this must be done in the desert. The process requires a detour: first, steam must be produced so that electricity can be produced using a conventional steam turbine. Mirrors which concentrate the light of the sun are used to produce the steam, in one of two ways: in the first, the concentration happens "in line" - for example in a mirror trench, where mirrors up to 100 metres long concentrate sunlight on liquid-filled tubes. The other technique concentrates sunlight on a single point, in solar towers or dishes.

The important point is that these mirror installations work only with direct sunlight, because diffuse light cannot be concentrated. The first reflective plants were built in Paris in about 1880, and were followed by other experiments during the early 20th century, notably in Egypt. The first systems did not produce electricity, only power to drive pumps, for example.

The production of electric current using thermo-reflecting mirrors was achieved for the first time in 1979. The construction of nine power stations, in particular at Kramer Junction, California, between 1983 and 1990, was an important step in the development of the technique. The thermo-reflector plants, with an output of 354 MW, are still in operation.

The major advantage of thermo-reflector systems is that they initially produce heat, which can easily be stored, which is important if you want to produce electricity after sunset. Solar panels produce electricity immediately, but storing it in accumulators is less efficient. Thermosolar power stations are also considerably cheaper than photovoltaic panels.

On the other hand, solar panels work with diffuse light, which means they can be used in northern countries, such as the Netherlands. Moreover, small-scale photovoltaic systems are always possible. In principle, thermo-solar power stations could generate electricity for the whole world. According to the calculations of DLR (the German air and Space Lab) they would only occupy 1% of the total area of deserts.

The DLR has drawn up a scenario in which, in 2050, thermosolar power stations could supply up to 25% of the world's electricity. The technique is growing strongly. Worldwide, over sixty projects are currently running, with a total output of at least 12,000 MW. A recent example is the installation of thermo-reflectors of 50 MW in the area around the Spanish city of Granada. The innovation in this case is that the plant includes a reservoir which can retain enough heat to continue producing electricity for seven and a half hours after sunset. The cost of the electricity is estimated at about 0.175 euros per kWh. The Netherlands could import electricity from the Sahara by constructing a high-tension line.

(from Milieu Magazine, Netherlands, www.milieumagazine.nl)

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