Environmental Engineering Reference
In-Depth Information
Depending on the type of concentrator, the CSP can be based on linear receivers (i.e.
parabolic trough or Fresnel collectors), or point focus receivers, such as solar towers
or parabolic dish systems. Linear concentrators, mainly parabolic trough collectors,
are currently the most proven solar thermal electric technology and are becoming
the reference technology for commercial applications. A summary of the CSP plants
operating globally is given in the Appendix.
Today, several companies are active in the field of solar thermal technologies. These
include Schott (Schott Solar), Acciona (Acciona Energy), Abengoa (Abengoa Solar),
Areva (Areva CSP), Siemens (Siemens Concentrated Solar Power) and Archimede Solar
Energy (Archimedes Solar Energy). This chapter introduces the principles of solar
thermal energy and discusses the advancements, as well as the potentiality, in power
production. The last section makes a comparison between the actual costs of CSP
versus competitive technologies.
14.2 SOLAR CONCENTRATION CONCEPT
INTHERMAL SYSTEMS
The sun has been worshipped as a life-giver to our planet since ancient times. Every
hour the amount of energy that the Earth intercepts is about 500 million TWh (values
at the top of the atmosphere) which corresponds to the total energy consumption of
the entire world over a thousand years. However, this energy is diluted in space: the
total integrated spectral irradiance has been made to conform to the value of the solar
constant accepted by the space community, i.e. 1366.1 W/m
2
.
The atmosphere along with atmospheric gases such as ozone (O
3
), oxygen (O
2
),
water (H
2
O) and carbon dioxide (CO
2
) strongly absorb light for some wavelengths.
Other causes of energy reduction occur once the irradiance has passed through the
atmosphere include scattering by aerosols and dust particles. By the time light reaches
the earth, total energy density is about 1000 W/m
2
for Air Mass 1.5.
As anticipated in the introductory paragraph, of the two technologies which con-
vert solar radiation into electricity, this chapter will focus on Concentrated Solar Power
plants. The power production process in CSP is based on two steps: the conversion
of solar energy into heat and then into power via a conventional thermodynamic
cycle.
The overall conversion efficiency can be seen as the product of each step:
η
= η
· η
(14.2.1)
ideal
th
carn
where
η
th
is the efficiency conversion of solar radiation in thermal power and
η
carn
stands for power cycle efficiency.
In order to fully understand the solar concentration concept and the advantages
of concentrating solar radiation, the two terms will now be discussed.
Starting with power cycle efficiency (
η
carn
), the second law of thermodynamics
states that the ideal conversion from thermal to mechanical power depends only on
the temperature of the heat source. The real conversion cycle will never achieve the
efficiency of the ideal cycle. However, the higher the efficiency of the thermody-
namic limit, the higher can be the real cycle efficiency. Using Carnot's cycle, which
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