Pressure drops, heat transfer coefficient, cost and power block structure for a direct storage parabolic trough power plant running molten salts

Abstract

Direct circulation of molten salts in the solar field of parabolic trough solar power plants may be a possible breakthrough to decrease their levelized cost of electricity. While prototypes are being erected around the world, this study addresses the main concerns and changes that are related to the replacement of thermal oils by molten salts, i.e. pressure drops, heat transfer coefficient, anti-freezing solutions, cost and power block design. It combines: 1) an analytical comparison of both technologies with respect to pressure drops and heat transfers; 2) simulations of a 50 MWe/7.5 h-of-storage power plant, using NREL’s SAM software, providing details on the dynamics of the outputs and parasitics. It has been observed the following: 1) pressure drops in the solar field are smaller running molten salts instead of thermal oil, thanks to higher operating temperature ranges; 2) HitecXL molten salt leads to lower electricity consumption than Therminol VP-1 oil and Solar Salt (parasitics); 3) a 6.3% reduction of the levelized cost of electricity when running HitecXL, ~14.80 c€/kWh, instead of Therminol VP-1, ~15.80 c€/kWh; 4) simpler power block designs can be considered for the higher operating temperatures of molten salts, resulting in higher efficiencies and/or cheaper power blocks.