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384 CHAPTER 12 Concentrating Solar Power

FIGURE 12.8
Solar thermal tower power plant with pressurized receiver using combined gas and steam
turbine cycle.
Courtesy V. Quaschning, Solar thermal power plants: technology fundamentals, Renew. Energy World (2003)
109e113.

reach efficiencies over 50%, whereas the efficiency of a simple steam turbine cycle
is only 35%. Therefore, solar system efficiencies of over 20% are possible
(Fig. 12.8).
The heliostat typically constitutes w50% of the energy system costs, and there-
fore it is important to optimize its design, size, weight, manufacturing volume, and
performance. These are important design variables, approached differently by devel-
opers, to minimize cost.
Energy storage is viewed as the next game changer in the power sector. Medium-
term thermal storage systems, with 5-h capacity per day, can be used to cover periods
of peak demands at nighttime. Long-term storage systems present thermal storage
capacity between 8 and 16 h, enabling the base load operation of power plants all
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night and in the early hours of the day, when required. In a CSP plant, thermal en-
ergy is stored before being converted to electricity. As a result, the round-trip effi-
ciency of CSP thermal storage can be close to 100%, much higher than any
electricity storage technology. However, CSP thermal energy storage (TES) can
only store thermal energy produced from the solar field, as opposed to other storage
technologies that can store electricity produced from any source.
The most common TES systems currently in use or under construction are based
on sensible heat storage using molten salts or synthetic oils. Some of the main

8
See footnote 1.