Solar Towers with Supercritical Steam Parameters - is the Efficiency Gain worth the Effort?

The concentrating solar power (CSP) industry is working intensively on cost reductions to increase the economic competitiveness of CSP plants. Efforts include new power plant concepts, optimised component manufacturing, as well ashigher steam parameter and these indeed lead to cost reductions over the last years. However, further improvements are required and this paper analyses the impact of supercritical steam parameters in CSP plants. A few decades ago the coal industry moved from subcritical Rankine cycle power plants, currently all CSP plants operate at subcritical conditions, to supercritical steam parameters to improve cycle efficiency. Many supercritical coal plants are now in commercial operation with significant engineering experience available in regards to plant design, construction and operation. The CSP industry can use this expertise to reproduce the benefits in their plants but some challenges also exist. Currently, supercritical CSP steam has only been shown at demonstration scale and the upscale to the smallest turbine size for supercritical parameters, being 250 MWe steam turbine capacity, is very significant. This paper compares three different 250 MWe (net) solar tower scenarios, one with subcritical and two with supercritical steam parameters. One supercritical power plant scenario is based on a novel high temperature stable molten salt that allows steam parameter of 620 °C at 280 bar and the second uses current molten salt and natural gas to reach supercritical conditions. The analysis shows that the net plant cycle efficiency can be raised from 41.3% in a subcritical to 44.2% in a supercritical concept, which translates into a levelised cost of electricity reduction of 4.3%. [ABSTRACT FROM AUTHOR]