Energy and Exergy Analyses of Recompression Brayton Cycles Integrated with a Solar Power Tower through a Two-Tank Thermal Storage System

Abstract

Energy and exergy analyses of a recompression supercritical carbon dioxide Brayton cycle integrated with a solar tower through a two-tank thermal storage system were conducted. A complete mathematical model, where a heliostat field was deployed and annually optimized is presented. This optimized heliostat field was then integrated with the supercritical carbon dioxide (sCO2) recompression Brayton cycle through a two-tank thermal storage system. Finally, exergy analysis was conducted for the entire integrated system. Molten salt was used as the medium in the storage tanks, and the analysis was performed for June 11, March 16, and December 1. The analysis was conducted for each complete day so that the storage system operated for 24 h without the need for any auxiliary heat source irrespective of the net power output of the integrated system. It was concluded that the highest and the lowest exergy destruction occurred in the central receiver system and the thermal storage system, respectively. For the month of June, the exergy destruction rate for the heliostat field and the solar tower is 1,295,65 and 156,254 kWh/day, respectively, which together constitute the total exergy destruction of the central receiver. In addition, the combined exergy destruction of all the components of supercritical carbon dioxide Brayton cycle is 138,432 kWh/day, and for thermal storage the exergy destruction rate is 4,735 kWh/day. Furthermore, the net energy efficiency of the whole system at solar noon for the month of June, March, and December is 6.93, 5.71, and 4.45%, respectively. Lastly, the electrical second law efficiency is 7.44, 6.14, and 5.4% for the months of June, March, and December, respectively. This analysis was conducted for Dhahran, Saudi Arabia, as an illustrative example of the developed model.