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Solar-farm power units

Parabolic channel collectors consist of arched mirrors, which bundle the sunlight onto an absorber tube directly lying in the caustic line. The length of such collectors is between 20 and 150 metres according to the type of construction. The concentrated solar radiation is transformed into heat within the absorber tubes and given to a circulating heat transfer medium. Due to cost reasons the parabolic channels are uniaxially aligned to the sun. Therefore, they are arranged in a north-south direction and are aligned to the sun from east to west in the course of a day. The collector field of a solar-farm power unit consists of many parabolic channel collectors which are switched in parallel.

Besides the parabolic channel collectors (PCC-modules) also Fresnel-mirror collectors (FMC-modules) are applied. They dispose of a secondary reflector above the absorber tube and get along with a smaller mirror surface at equal efficiency. As a heat transfer medium either thermo-oil or overheated steam is applied. With thermo-oil plants you can achieve temperatures up to 390° C which are used in a heat exchanger for steam production and then are lead to a conventional steam turbine. The direct steam production (DISS = Direct Solar Steam) doesn’t need such heat exchangers, as the overheated steam is directly produced within the absorber tubes. Therewith, you can achieve temperatures of more than 500° C. Solar-farm power units have been run commercially since 1984. The 9 SEGS-power units (SEGS = Solar Electricity Generation System) in South California produce 354 MW capacity in total. At the time being, another power unit with a capacity of 65 MW is being built in Nevada and is scheduled to be connected to the net in the year 2007. The efficiency factor of this type of power unit is indicated with 14 %.