Page 144 - A Comprehensive Guide to Solar Energy Systems

Chapter 7 • Concentrating Solar Thermal Power 143

FIGURE 7.10 One of the parabolic dishes installed at the Plataforma Solar de Almería (www.psa.es).

(http://www.robertstirlingengine.com/principles.php). The absorber of the Stirling
engine is placed at the focal point of the solar concentrator and the thermal energy
transferred to the working fluid (usually hydrogen or helium) at the absorber is con-
verted into mechanical energy by the Stirling engine, which drives a small electricity
generator (<50 kW e ). These systems are very modular (the dish diameter is usually
smaller than 10 m) and can be used to supply electricity to small consumers.
The Stirling dish CST systems have the highest solar to electric efficiency with peak effi-
ciency values greater than 30% having been reported. However, no commercial CSTP plant
using this technology is currently in operation because of the reliability problems showed
by the Stirling engines when working at the high-pressures (15–20 MPa) and temperatures
(>600°C) required to achieve high efficiencies and become competitive with the other CST
technologies. It seems that the commercial deployment of this technology will not take
place until the problems with the Stirling engine are solved. many companies (Stirling En-
ergy Systems, InFInIA, SOlO, Tessera Solar, etc.) have unsuccessfully devoted great efforts
to solve these problems. meanwhile, a few experimental units of Stirling dishes are being
tested worldwide, such as the units installed at the Plataforma Solar de Almería (www.psa.
es). This research establishment is the largest public research and development (R + d)
centre devoted to CST technologies in the world.

7.6 Technology Trends

The main challenge for CSTP plants at present is the achievement of a significant cost re-
duction in the short term so as to become more cost-effective and competitive with other
renewable energy options for electricity production (i.e., wind farms and photovoltaic
plants). The significant cost reduction recently experienced by PV plants is a major barrier