Solar thermal concentrating solar power (CSP) plants, because of their capacityfor large-scale generation of electricity and the possible integration of thermal storage devices and hybridization with backup fossil fuels, are meant to supply a significant part of the demand in countries of the solar belt. Nowadays, the market penetration of solar thermal electricity is steeply increasing, with commercial projects in Spain, USA, and other countries, being the most promising technology to follow the pathway of wind and photovoltaics to reach the goals for renewable energy implementation in 2020 and 2050. In the first commercial projects involving parabolic-trough technology, some improvements are being introduced like the use of large molten-salt heat storage systems able to provide high degrees of dispatchability to the operation of the plant, like the plants Andasol in Guadix, Spain, with 7.5 h of nominal storage, or the use of direct steam generation loops to replace thermal oil at the solar field. In the near future, the research and innovation being conducted within the field of linear Fresnel collectors may lead to high temperature systems able to operate up to 500 • C and produce cost-effective superheated steam. Central receiver systems are opening the field to new thermal fluids like molten salts (Gemasolar tower plant in Seville, Spain) with more than 14 h of nominal storage and air, and new solar receivers like volumetric absorbers, allowing operation at temperatures above 1000 • C. All these factors can lead to electricity generation cost reduction of CSP plants by 30-40% for the period 2010-2020, according to public roadmaps and cost analysis made by the International Energy Agency in PTCs are linear-focus concentrating solar devices suitable for working in the 150-400 • C temperature range. 20 The current research with new thermal fluids intends to increase the operating temperature up Advanced Review 4 5
CONCLUSION AND OUTLOOKFrom the seventies to the nineties, the development of STE technologies remained restricted to a few FIGURE 9 Aerial view of Gemasolar plant, property of Torresol Energy C Torresol Energy, located in South Spain. At present, it is the largest commercial solar central receiver system with a circular-shape heliostat field. Reproduced by permission of Torresol Energy.