Performance of S-CO₂ Brayton Cycle and Organic Rankine Cycle (ORC) Combined System Considering the Diurnal Distribution of Solar Radiation

This paper researches the performance of a novel supercritical carbon dioxide (S-CO₂) Brayton cycle and organic Rankine cycle (ORC) combined system with a theoretical solar radiation diurnal distribution. The new system supplies all solar energy to a S-CO₂ Brayton cycle heater, where heat releasing from the S-CO₂ cooler is stored in the thermal storage system which is supplied to the ORC. Therefore, solar energy is kept at a high temperature, while at the same time the thermal storage system temperature is low. This paper builds a simple solar radiation diurnal distribution model. The maximum continuous working time, mass of thermal storage material, and parameter variations of the two cycles are simulated with the solar radiation diurnal distribution model. 10 organic fluids and 5 representative thermal storage materials are compared in this paper, with the mass and volume of these materials being shown. The longer the continuous working time is, the lower the system thermal efficiency is. The maximum continuous working time can reach 19.1 hours if the system provides a constant power output. At the same time, the system efficiency can be kept above 38% for most fluids.