Thermodynamic cycles for solar thermal power plants: A review

Solar thermal power plants for electricity production include, at least, two main systems: the solar field and the power block. Regarding this last one, the particular thermodynamic cycle layout and the working fluid employed, have a decisive influence in the plant performance. In turn, this selection depends on the solar technology employed. Currently, the steam Rankine cycle is the most widespread and commercially available option, usually coupled to a parabolic trough solar field. However, other configurations have been implemented in solar thermal plants worldwide. Most of them are based on other solar technologies also coupled to a steam Rankine cycle, although integrated solar combined cycles have a significant level of implementation. In the first place, power block configurations based on conventional thermodynamic cycles—Rankine, Brayton, and combined Brayton–Rankine—are described. The achievements and challenges of each proposal are highlighted, for example, the benefits involved in hybrid solar source/fossil fuel plants. In the second place, proposals of advanced power block configurations are analyzed, standing out: supercritical CO2 Brayton cycles, advanced organic Rankine cycles, and innovative integrated solar combined cycles. Each of these proposals shows some advantages compared to the conventional layouts in certain power or source temperature ranges and hence they could be considered attractive options in the medium term. At last, a brief review of proposals of solar thermal integration with other renewable heat sources is also included.