Alternative cycles based on carbon dioxide for central receiver solar power plants

Research in concentrated thermal solar power plants of all types and, in particular, those based on central receiver, namely solar tower plants, has experienced great impetus in the last decade, reaching full commercial operation with the PS10 plant in Spain. In spite of previous demonstration plants testing different receivers and power cycle layouts, this first commercial power plant adopted a cavity receiver generating saturated steam and therefore penalising cycle efficiency in order to gain plant reliability. According to the experience gained, if a competitive Levelised Cost of Electricity is to be reached, capital and maintenance costs must be reduced and efficiencies must be increased. To achieve these goals, modifying the power cycle is deemed essential, whether using superheated steam or alternative fluids. In this work, the use of supercritical and transcritical carbon dioxide cycles for this application is proposed. Three different cycles are considered, the first two of which are stand-alone closed cycle gas turbines using carbon dioxide. The third proposal is a combined cycle that comprises a topping carbon dioxide gas turbine and a bottoming Organic Rankine Cycle. Preliminary results show that these cycles are promising technologies for solar tower plants, having the potential to compete in terms of efficiency and costs with other conventional technologies.