Helium Gas Brayton Cycle and Rankine Cycle Combined System with PCM Thermal Storage for Efficient CSP System

For a Concentrating Solar Power (CSP) plant to achieve high thermal efficiency and maintain operation during nighttime, high temperature heating and the integration of thermal energy storage in the system is important, which becomes even more critical for the cost competitiveness of the CSP against solar PV technologies. To achieve the goal, the current work proposes a concentrating solar thermal power plant to have combined thermal cycles—a Brayton cycle (helium gas) at high temperatures (800-850 °C) alongside a Rankine cycle (water). The water in the Rankine cycle takes the energy from the helium gas cooling process in Brayton cycle to generate steam. To get a high concentrating solar receiving efficiency and high temperature in the solar receiver, a novel jet impingement heat transfer approach has been proposed for helium gas to be heated. For compact and large quantity (16 hours) thermal energy storage at temperatures ≥800 °C, NaCl has been selected as a suitable Phase Change Material (PCM) due to its appropriate melting point (801°C), high heat of fusion (481.8kJ/kg), and large reserves and relatively low cost among many high temperature PCMs. The feasibility of the proposed CSP system is studied through basic thermodynamic analysis to the combined cycles, examination of solar receiver heat transfer of jet impingement, and calculation of PCM thermal energy storage capacity. A thermal efficiency of 43.8-45.2% was found achievable for the thermal power system. The solar receiving efficiency can approach 89.2%. If the total solar energy in a field going to the solar receiver can achieve 90%, then the energy from solar field can have 35.2-36.3% being converted to electrical energy in such a CSP power plant that can produce electrical power 24 hours a day.