Page 142 - A Comprehensive Guide to Solar Energy Systems

Chapter 7 • Concentrating Solar Thermal Power 141

FIGURE 7.8 Scheme of the Plant GEMASOLAR with a molten-salt central receiver and thermal storage system.
Courtesy of SENER Ingeniería.

to the PCS used in plants with PTC. The main difference is the steam temperature deliv-
ered to the steam turbine. Although the steam produced in the PS-10 and PS-20 plants
5
is saturated steam at 240°C and 40 ×10 Pa due to lack of suppliers at that time for a
central receiver with higher temperature, the later use of molten salt receivers increased
the superheated steam temperature up to 550°C, thus significantly increasing the PCS
efficiency, and therefore, the overall plant efficiency. The state-of-the-art of CSTP plants
with central receiver is based on the use of molten salt as both working fluid in the re-
ceiver and storage media in the thermal storage system, as depicted in Fig. 7.8.
A very important environmental parameter that must be evaluated before building a
CSTP plant with a central receiver is the local atmospheric attenuation, because at least 15%
of the solar radiation reflected by the heliostats located at the outer part of the solar field can
be absorbed by the air before reaching the receiver. This property is especially important in
desert and windy areas because dust particles in the air absorb a significant amount of the
radiation reflected by the heliostats that are placed far away from the receiver.

7.4 Compact Linear Fresnel Concentrators

Fig. 7.9 shows a typical linear Fresnel concentrator (lFC) with its long rectangular reflec-
tors that can rotate independently from each other to reflect the incoming direct solar ra-
diation toward the receiver tube located above the reflectors. The solar radiation reflected
by each rectangular mirror overlap onto the receiver tube and the flux density is thus
increased. The working fluid circulating through the receiver tube is heated as it circulates