Maximizing the power block efficiency of solar tower plants: Dual-pressure level steam generator

Abstract

Solar tower plants (STP) are one of the most promising renewable technologies to substitute conventional power plants. To further increase its penetration in electricity markets, it is necessary to maximize its efficiency. This work addresses the challenge of increasing the inlet pressure up to 165 bar at the high pressure turbine (HPT) to improve the power block efficiency. Nowadays, these plants operate Rankine cycle with reheating using steam at 126 bar at the inlet of the HPT. This pressure is limited in current STP by the working temperatures of the molten salt, which range from 285 °C and 565 °C, the pinch point temperature difference in the evaporator and the current steam generator (SG) layout. A new steam generator design with dual-pressure level evaporation is proposed. The heat exchangers that form the SG are designed thermomechanically and the power cycle performance is analyzed using the first and second laws of thermodynamics. The results show that the novel dual-pressure level SG layout increases the power block efficiency from 44.14% to 44.64%. Assuming a market pricing scenario of two-tier tariff and a power purchase agreement price of 16.3c€/kWhe, the new SG layout yields an extra economic benefit of 623 k€ per year due to an increase of energy produced of 5.71 GWhe/year.