MW Level Solar Powered Combined Cycle Plant with Thermal Storage: Thermodynamic Performance Prediction

Abstract

The renewable resource, mainly the solar energy, can be used to produce electric energy on a large scale in solar thermal power stations, which concentrate sunlight at temperatures which range between 200^O to 1200^O C and even more. This paper presents a conceptual configuration of a solar powered combined cycle power plant with a topping air Brayton cycle and a bottoming steam Rankine cycle. The conventional GT combustion chamber is replaced by a high-temperature solar thermal air heating system. During the daytime, a part of the exhaust air from the gas turbine (GT) is bypassed to produce superheated steam in HRSG, which in turn runs a steam turbine and the remaining exhaust air from GT is utilized to charging molten salt, which acts as a storage medium. The heat energy of the molten salt is utilized to generate steam for 4 hours in another HRSG, when sunlight is not available.

From the thermodynamic analysis, it is found that for the base case GT pressure ratio of 4, power obtained from the GT block is 1.75 MW, while total power obtained from the combined cycle is 2.28 MW. The overall thermal efficiency of the combined cycle at this pressure ratio is 25.39%. The pressure ratio of the gas turbine has been varied from 2 to 20 and the optimum pressure ratio has been found out where total power output of the combined cycle plant is maximum.