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Solar thermal power plants Electricity from bundled sunbeams

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Solar thermal power plants use mirrors to bundle the sun's rays. As with a burning glass, they generate heat and convert this energy into electricity. The best way to do this is in the glaring glow of the desert sun.

Status: 04.12.2019

A solar thermal power plant, also known as a solar thermal power plant, converts the sun's radiation into heat. In contrast to solar collectors, it does not use the heat directly, but uses it to generate electricity. There are different designs of solar thermal power plants. However, the basic principle is the same for all of them: sunlight is bundled and heats a liquid or vapor. This can be used to drive turbines that use generators to generate electricity.

Principle of a parabolic trough power plant

In a parabolic trough power plant, curved mirrors bundle the incident sunlight in a focal line. There is a thin absorber pipe in which there is water vapor or a thermal oil. The solar radiation heats the contents of the pipe to several hundred degrees Celsius, which is then conducted to turbines via pipes. Most of the time, the trough-shaped mirrors are constantly tracking the sun so that the system can generate as much energy as possible throughout the day.

Solar tower power plant

The sunlight can also be focused in a single point. The best-known design for this method is the solar tower power plant: Hundreds of computer-controlled burning mirrors direct the sunlight onto the top of a tower. At the focal point there is a comparatively small absorber in which it can get around 1,000 degrees Celsius. The thermal energy is used to produce steam that drives turbines with generators.

Electricity in any weather and around the clock

Parabolic mirrors in the solar thermal power plant near Las Vegas.

Solar thermal power plants have a relatively low level of efficiency. They have one major advantage over photovoltaic systems: The heat obtained from sunlight can be stored, for example in liquid salt tanks or blocks made of high-temperature concrete. At night or in bad weather, the energy is then released again and drives the turbines. In times of low solar radiation, for example in winter, the heat required to generate electricity can also be generated differently, something with a gas-fired power plant coupled to the system. Solar thermal power plants could therefore continuously supply electricity and thus cover the base load in the electricity network.

Solar thermal power plant in Jülich

In 1985, the first commercial solar thermal power plant in the USA went into operation in Kramer Junction, California. Further plants are in the states of Nevada, California, Arizona and Florida. Solar thermal energy is also used in Europe: In Andalusia, the Planta Solar power plant has been feeding electricity into the Spanish grid since 2007. Since then, a number of systems have been added in sunny southern Spain. In Germany, on the other hand, there is only one experimental power plant in Jülich.

Desertec - the dream of solar power from the desert

Desertec was a highly ambitious project with the aim of generating energy where renewable sources are abundant. The electricity should either be consumed on site or transferred over long distances using high-voltage lines. The focus was on the idea of ​​building solar thermal power plants in North Africa and directing the electricity they produce across the Mediterranean to Europe. The German Aerospace Center (DLR) calculated 17 percent of Europe's electricity demand in 2009. The DLR also forecast the costs: the construction of 50 solar thermal power plants and the high-voltage lines should cost 400 billion euros by 2050. In view of this amount, many German industrial and financial companies took part in the desert electricity project, but withdrew from the project after a while. Reasons for this were, among other things, doubts about the financial viability and the uneasy political situation in North Africa.

Success for solar thermal in Morocco

NOORo III, part of the huge solar power plant in Morocco

Desertec was not without consequences. Morocco continued its plans for solar thermal power plants, even when the Desertec project was underway in the desert sands. A prestigious example is the NOORo plant near the city of Ouarzazate on the edge of the Sahara. The plant extends over an area of ​​30 square kilometers, on which there are four power plant units. NOORo 1 and 2 are parabolic trough power plants with a maximum output of 160 and 200 megawatts, respectively. NOORo 3 is a solar tower power plant, the tower of which rises 247 meters. The maximum output is 150 megawatts. NOORo 4, on the other hand, generates a maximum of 72 megawatts with photovoltaics. The maximum total output of NOORo is therefore 582 megawatts. For comparison: Germany's most powerful nuclear power plant, Isar 2 near Landshut, has a capacity of almost 1,500 megawatts. The NOORo project was financed by many donors from abroad. The German KfW Bank was among them.