17 - Solar power towers using supercritical CO2 and supercritical steam cycles, and decoupled combined cycles

Abstract

Solar power-tower systems (also known as central receiver systems) can efficiently achieve high temperatures because of the high concentration ratios they can achieve using different configurations of the collector field and receiver. The combination of solar power towers with high-temperature cycles permits to increase in the global efficiency in the conversion of solar radiation to electricity with respect to concentrated solar power (CSP) plants based on the sub-critical Rankine cycle and could result in levelized cost of energy (LCOE) reduction, as far as the increase in efficiency outweighs the increased costs associated with the use of more expensive equipment and materials. Although operating temperatures higher than 1000°C can be achieved with solar power towers, there are still significant technological barriers that must be overcome before CSP plants operating at these elevated temperatures reach the market. The use of supercritical power cycles operating at temperatures in the range 600–800°C, only moderately higher than those of the current CSP plants, has been identified as a promising path to increase the efficiency and reduce the LCOE of the next generation of CSP plants that would require technological developments achievable in the short to medium term. Another option to increase the efficiency of concentrated solar thermal (CST) plants that requires only incremental technology developments is the concept known as decoupled solar combined cycles, based on a high-temperature topping cycle whose rejected heat is used to charge a thermal energy storage system which, in turn, feeds a bottoming cycle. The concepts presented in this chapter are excellent candidates to become the next generation(s) of commercial CST plants, although in some cases significant technology developments are required.