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Concentrated Solar Power using supercritical CO 2 (S-CO 2 ) recompression Brayton cycles offer advantages of similar and even higher overall thermal efficiencies compared to power cycles using superheated or supercritical steam. The high efficiency and compactness of S-CO 2 , as compared with steam Rankine cycle at the same high temperature, make this cycle attractive for central receiver applications, since both attributes lead to decrease in levelized cost of energy and therefore make this technology economically feasible. The current research in S-CO 2 is focused on thermodynamic analysis and system components. In this paper energy and exergy analyses of a supercritical CO 2 Recompression Brayton cycle are presented. Energy, exergy and mass balance are carried out for each component and first law and exergy efficiencies are calculated with and without reheat scenarios. Optimization is then carried out by using Sequential Least SQuares Programming (SLSQP) and optimum operating conditions based on maximum first law efficiency are determined. The results showed that the exergy efficiency reaches a maximum value at 600 °C while the first law efficiency increases monotonically with highest temperature of the cycle.

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A high-temperature, high-pressure solar receiver was designed as part of the advanced thermal energy storage project carried out in collaboration with Abengoa Solar NT at CSIRO Energy Centre in Newcastle, Australia, with support through the Australian Renewable Energy Agency (ARENA). The cavity-type receiver with tubular absorbers was successfully installed and commissioned, using concentrated solar energy to raise the temperature of CO2 gas to 750 °C at 700 kPa in a pressurized, closed loop system. Stand-alone solar receiver tests were carried out to investigate the thermal characteristics of the 250 kWt solar receiver. The on-sun full-load test successfully achieved an outlet gas temperature of 750 °C while operating below the maximum allowable tube temperature limit (1050 °C) and with a maximum pressure drop of 22 kPa. The corresponding estimated receiver thermal efficiency values at full flow rate were 75% estimated based on measured receiver temperatures and heat losses calculations for both single aim-point and multiple aim-point heliostat control strategies. The use of a quartz glass window affixed to the receiver cavity aperture was tried as a means for improving the receiver efficiency by reducing convective heat losses from the receiver aperture. However, while it did appear to significantly reduce convective losses, a more effective metal support frame design is necessary to avoid damage to the window caused by stresses introduced as a result of distortion of the supports due to heating by the spillage of rays from the heliostat field.