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374 CHAPTER 12 Concentrating Solar Power

for CSP systems based on Brayton or Rankine cycles. The basic and general process
for conversion of solar thermal energy to electric energy in the concentrated power
plants is shown schematically in Fig. 12.1.
Energy is recovered by solar collectors, which are mechanical devices that cap-
ture radiant solar energy and convert it to useful thermal energy. This energy can be
stored (if appropriate or required) and converted to satisfy electricity, thermal, or
mechanical energy demands. Different types of solar collectors can be applied,
depending on the application.
There are nonconcentrating and concentrating types of solar collectors. The
former uses the same area to intercept and absorb solar radiation. However, the
concentrating solar collectors used in CSP plants usually have concave reflecting
surfaces to intercept and concentrate solar radiation into a small receiving area,
thereby increasing radiation flow. Parabolic troughs, solar towers in heliostat field,
linear Fresnel reflectors (LFRs), and parabolic dishes (PDs) are the main technolo-
gies used in the concentrating solar thermal power plants, due to the production of
high-temperature heat. Fig. 12.2 represents the concept involved in the solar concen-
trator: (1) parabolic trough, (2) PD, (3) power tower, and (4) linear Fresnel.
As sunlight is not always available, an energy storage system is required to
extend the working hours of a solar energy plant to satisfy energy demands during
the nighttime, for example. Integration of energy storage systems with CSP technol-
ogies enables the prolongation of the operation hours of solar power plants and could
mitigate the dependence and direct relationship between CSP technologies and

Electric
energy

mechanical
fluid fluid steam energy
collector heat
system storage boiler engine generator
thermal thermal thermal
energy energy energy

Heat Waste
rejected Heat
FIGURE 12.1
A generic concentrating solar power plant.
Courtesy L. Witmer, Overview of Solar Thermal Power Systems j EME 811: Solar Thermal Energy for Utilities and
Industry [WWW Document], Pennsylvania State Univ., 2017. URL: https://www.e-education.psu.edu/eme811/
node/682.