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Solar Power Sources: PV, Concentrated PV, and Concentrated Solar Power 31

2.4.1.1 Parabolic Trough
The focal point in solar parabolic linear reflectors can be found along their length (see Figure 2.15).
A receiver pipe with a fluid (oil or molten salt) is running along the inner part of the curved surface.
The concentrated solar energy heats the fluid flowing through the pipe, and the heat energy is then
used to generate electricity in a conventional steam generator. Trough designs can incorporate ther-
mal storage allowing for electricity generation during the evening [27, 32], and the thermal storage
will also be briefly discussed later in this chapter.

2.4.1.2 Linear Fresnel Reflector
This kind of technology approaches the parabolic trough collectors but uses an array of flat or
slightly curved mirrors to collect the sun rays onto a fixed receiver mounted on a linear tower (see
Figure 2.16) [28, 33]. The linear Fresnel reflector (LFR) field can be pictured as a broken-up para-
bolic trough reflector, but it needs less land to generate a specific output. Its major asset is that it
uses flat or elastically curved reflectors, which are cheaper compared to parabolic glass reflectors.
However, LFRs are less efficient than troughs in converting solar energy to electricity and it is more
difficult to incorporate storage capacity into their design [33].

2.4.1.3 Solar Towers
Solar towers (see Figure 2.17), also known as central receiver systems, utilize hundreds or thousands
of small reflectors (called heliostats) to collect the sunlight on a central receiver mounted on the top
of a fixed tower. The working fluid (mostly sea water) is heated and later drives a turbine to produce
electrical power [29]. In this design, very high temperatures are reached; therefore, an increase in
efficiency is marked resulting in less cost of thermal storage. Temperatures reached in a solar power
tower can be greater than 1000 °C [32].

FIGURE 2.15 Parabolic trough line concentrator for CSP. (From Argonne National Laboratory, Solar
Energy Development Programmatic EIS (Information Center), Solar Energy and Electric Transmission Photos,
Available: http://www.solareis.anl.gov/guide/photos/index.cfm, Retrieved on January 18, 2017.)