Analysis and comparison of solar-heat driven Stirling, Brayton and Rankine cycles for space power generation

This paper presents an analysis of solar-heat driven Brayton, Rankine and Stirling cycles operating in space with different working fluids. Generation of power in space for terrestrial use can represent a great future opportunity: the low-temperature of space (∼3 K), allows the attainment of very high efficiency even with low-temperature heat inputs, and the solar energy input is higher in space than on earth. This paper shows a comparative analysis of advanced Brayton, Rankine and Stirling cycles to improve the understanding of the optimal trade-off between high efficiency and the smallest needed heat rejection area. The effect of the main cycles' operational parameters and plant layouts on efficiency and power to radiator area ratio have been analyzed. The thermal efficiency of regenerative-reheated-intercooled Brayton cycle was found to be the best among the investigated configurations. The power to radiator area ratio was found to increase with the introduction of reheating for both the Rankine and Brayton cycles. Stirling cycles efficiencies are lower than those obtained by the Brayton and Rankine cycles but with values of power to radiator area ratio equal to about half of those obtained by Brayton cycles but much higher than those obtained by the Rankine cycles.