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Solar Power Sources: PV, Concentrated PV, and Concentrated Solar Power 33

FIGURE 2.18 Schematic view of a parabolic dish solar system. (From Sandia National Laboratories, Image
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.)

highest solar-to-electric conversion performance of any CSP system [32]. However, the need for a
heat transfer fluid throughout the collector field raises design issues, such as piping layout, pumping
requirements, safety, and thermal losses.

2.4.2 CSP and Storage

The intermittency and unreliability of solar energy may impact the performance of a solar thermal
plant, which consists of the solar field, the heat transfer fluid transport system, and the power block.
Consequently, there will be a mismatch in energy supply and demand, especially at night or due to
clouds’ shading effect during a day. In operated solar thermal plants, this imbalance is evened by
using either auxiliary fossil fuel burners or heat storage systems. Therefore, the requirement for
thermal-energy storage systems strongly depends on the daily and yearly variation of solar radiation
and the electrical consumption profile.
Heat storage systems store the excess of thermal energy when solar radiation is above the base
load output of the CSP and deliver it on the power block’s steam generator when it is needed. In
that way, the power output of the plant during cloudy days is increased, in addition to its operating
time beyond sunset. Hence, not only is energy supply secured, but also solar thermal power plants
become more competitive for grid connection [35].
The selection of the appropriate storage capacity is site and system dependent. Feasibility studies
need to be performed considering statistical analysis of the electrical demand, as well as the site-
specific weather conditions. Moreover, economic trade-off analysis is necessary to be carried out in
order to select the optimum storage capacity and the optimum system.
Heat storage systems can be found into two basic classifications: active and passive systems.
In active systems, the heat storage medium is a moving, circulating liquid, which stores and deliv-
ers the sensible heat, whereas passive heat storage systems can store either sensible or latent heat