Advanced Review Solar thermal CSP technology Manuel Romero ∗ and Jos ´ e Gonz ´ alez-Aguilar Solar thermal concentrating solar power (CSP) plants, because of their capacity for 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 2010. C  2013 John Wiley & Sons, Ltd. How to cite this article: INTRODUCTION S olar thermal electricity or STE (also known as CSP or concentrating solar power) is expected to impact enormously on the world’s bulk power supply by the middle of the century. 1 Nowadays, the high-temperature thermal conversion of concen- trated solar energy is rapidly increasing, with many commercial projects taken up in Spain, USA, and other countries such as India, China, Israel, Australia, Algeria, and Italy. Spain with 2400 MW connected to the grid in 2013 is taking the lead on current commer- cial developments, together with USA where a target of 4500 MW for the same year has been fixed and The authors have declared no conflicts of interest in relation to this article. * Correspondence to: manuel.romero@imdea.org IMDEA Energ´ ıa, Avda. Ram ´ on de la Sagra 3, M ´ ostoles, Spain DOI: 10.1002/wene.79 other relevant programs like the `Solar Mission’ in India recently approved and going for 22 GW-solar, with a large fraction of thermal. 2 Only in Southern Europe, the technical potential of STE is more than 1000 GW and in Northern Africa it is immense. 3 Worldwide, the exploitation of less than 1% of the total solar thermal power plant potential would be enough to meet the recommendations of the United Nations’ Intergovernmental Panel on Climate Change for long-term climate stabilization. 4 One megawatt installed concentrating solar thermal power avoids annually 688 tons of CO 2 compared with a combined cycle conventional plant, which uses natural gas and 1360 tons of CO 2 com- pared with a conventional coal/steam plant. A 1-m 2 mirror in the primary solar field produces 400 kWh of electricity per year, avoids 12 tons of CO 2 com- pared with a conventional coal/steam plant and con- tributes to a saving of 2.5 tons of fossil fuels during its 25-year operation lifetime. The energy payback time for the materials of CSP systems is less than 1 year, 5  2013 John Wiley & Sons, Ltd. Volume 3, January/February 2014 42 WIREs Energy Environ 2014, 3:42–59. doi: 10.1002/wene.79