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Concentrating Solar Thermal Power

Eduardo Zarza-Moya

CIEMAT-PSA, ALMERÍA, SPAIN
Eduardo.zarza@psa.es

7.1 Introduction

There are many technologies that convert solar radiation into electricity. Although the
most popular systems are the photovoltaic (PV) systems, there exist other technologies to
convert solar radiation into electricity. Concentrating solar thermal power (CSTP) systems
convert direct solar radiation into thermal energy at a medium or high-temperature (from
125°C to even above 1000°C) and the thermal energy is then converted into electricity us-
ing a thermodynamic cycle. The more common cycles used nowadays are: Brayton, Ran-
kine, or Stirling cycles.
Historically only concentrating solar power (CSP) was universally referred to and was
used in place of solar thermal electricity (STE). Only in recent years has the term STE
become widespread and some organizations have moved the CSP definition to a higher
level to include both STE and concentrating photovoltaics (CPV). However, some orga-
nizations still use CSP to refer to and in place of STE, and in these cases CSP does not
include CPV. Therefore, the meaning of CSP varies among organizations; it is without
a clear definition and is an ambiguous term, and is not used in this chapter. The term
concentrating solar thermal (CST) is used globally to refer to the technologies used to
concentrate and convert solar radiation into thermal energy (i.e., CST technology or
technologies). In this chapter concentrated solar thermal power refers to electricity gen-
erated using CST technologies.
Fig. 7.1 shows the simplified scheme of a typical CSTP system. Starting from the pri-
mary energy source (i.e., the direct solar radiation), the first component is the optical con-
centrator, which increases the flux density of the direct solar radiation, so that the solar
flux density on the surface of the receiver may be of up to several thousand times higher
than the flux density of the direct solar radiation reaching the Earth’s surface. The latter is
usually of the order of, or lower than, 1000 W m . This concentration is usually achieved
−2
by reflecting the collected direct solar radiation onto a receiver with a surface smaller than
that of the concentrator. The concentrated solar radiation reaching the receiver’s outer sur-
face is converted into thermal energy by increasing the enthalpy of a working fluid as it cir-
culates inside the receiver. Several working fluids are used nowadays (e.g., water, thermal
oils, molten salts, or air).

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