Physics of Energy Sources by GEORGE C. KING

Author:GEORGE C. KING
Language: eng
Format: epub
ISBN: 9781118698426
Published: 2017-03-23T00:00:00+00:00

Figure 4.30 (a) Schematic diagram of a parabolic trough concentrator. Solar radiation is concentrated by parabolic mirrors onto a pipe that runs along the focus of the mirrors. The pipe carries synthetic oil which is heated by the solar radiation. Each mirror can be rotated about the axis containing the pipe to track the position of the Sun. (b) The focusing action of the parabolic mirrors.

Central receiver with heliostats

This system consists of a large number of plane mirrors, called heliostats. These mirrors reflect sunlight onto a central receiver that is placed on top of a tower, as illustrated in Figure 4.31. The mirrors are mechanically rotated about two perpendicular axes to track the position of the Sun. Very high temperatures, ∼550°C, can be reached and so molten salt is used as the working fluid. The molten salt is stored in a tank. This stores the thermal energy of the molten salt and it is important to note that it is much easier to store thermal energy than it is to store electricity. Salts are an effective storage medium because they have a high specific heat capacity and are low-cost. The molten salt can be used directly to heat water to drive steam turbines. Alternatively, the stored molten salt can be used to drive the turbines at night or during days when the Sun is not shining. The Gemasolar Solar Power Facility, which is situated in Fuentes de Andalucía, Spain, was the first commercial-scale plant in the world to use a central tower receiver and thermal energy storage technology using molten salt. A photograph of the facility is shown in Figure 4.32. It has 2650 heliostats, which have a total reflective area of 304 750 m2, and produces an electrical power of ∼20 MW. The inclusion of the molten salt heat storage system enables independent electrical generation for up to 15 hours without any solar radiation.

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