High-efficiency thermodynamic power cycles for concentrated solar power systems

This paper provides a review of high-efficiency thermodynamic cycles and their applicability to concentrating solar power systems, primarily focusing on high-efficiency single and combined cycles. Novel approaches to power generation proposed in the literature are also highlighted. The review is followed by analyses of promising candidates, including regenerated He-Brayton, regenerated CO2-Brayton, CO2 recompression Brayton, steam Rankine, and CO2-ORC combined cycle. Steam Rankine is shown to offer higher thermal efficiencies at temperatures up to about 600 °C but requires a change in materials for components above this temperature. Above this temperature, CO2 recompression Brayton cycles are shown to have very high thermal efficiency, potentially even exceeding 60% at 30 MPa maximum pressure and above 1000 °C maximum temperature with wet cooling. An estimate of a combined receiver and power cycle operating temperature is provided for the cycles considered and compared to the traditional approach of optimization based on the Carnot efficiency. It is shown that the traditional approach to optimizing the receiver and turbine inlet temperatures based on Carnot is generally not sufficient, leading to an optimum temperature shift of more than 100 °C from the Carnot case under various conditions.