4E Transient Analysis of a Solar-Hybrid Gas-Turbine Cycle Equipped with Heliostat and MED

Abstract

The current study investigates a cogeneration cycle of power and freshwater integrated with a solar system. The solar system is of the heliostat type, which is considered to preheat the inlet air in the combustion chamber of a 25-MW gas turbine. The waste heat of the turbine output stream is used to produce freshwater. Parameters such as the ambient temperature and solar irradiance significantly affect the system’s performance; hence, all analyses, including those pertaining to energy, exergy, economics, and environment, were conducted transiently, with a one-hour time step throughout the year so that the impacts of these effective parameters could be examined. Besides the analysis assuming a constant mass flow rate for the air entering the compressor, the calculations were repeated with the assumption of a constant volumetric flow rate to evaluate the cycle in the same conditions as those of natural gas power plants. Given the constant volumetric flow rate, for every 10-degree increase in temperature, the compressor power consumption decreased by approximately 2%. Moreover, a sensitivity analysis of the cycle performance in terms of ambient temperature was performed, and the corresponding results are presented. Finally, some correlations are presented to estimate variations in compressor power consumption and net turbine power due to temperature variations. The results demonstrate that in Bushehr, Iran, every one-degree increase in ambient temperature leads to an approximately 0.67 percentage decrease in net-generated power. In the end, the performance of the cycle was investigated under climatic conditions and solar irradiation intensities in several cities in Iran and some cities in different countries in which heliostat power plants have already been established. The results obtained in these cities were compared; it was concluded that the lowest annual cost of electricity generation is related to Isfahan in Iran, which reduces the cost of electricity generation by more than 20% (2.32 Cents/kWh) compared to the base cycle.