High-temperature molten-salt thermal energy storage and advanced-Ultra-supercritical power cycles

Abstract

The work explores the opportunities offered by higher temperature heat transfer/heat storage fluids, and higher temperature power cycles, in higher concentration solar thermal power plants. The goal is to design a renewable energy plant able to supply fully dispatchable electricity to the grid at a cost, inclusive of dispatchability, better than using wind and solar photovoltaic with external energy storage by batteries. By increasing the receiver/hot tank temperature from 565-575 to 730°C, the efficiency of the thermal cycle increases by 30% vs. current plants working with conventional steam Rankine cycles (thermal efficiency η∼52% vs. present η∼40%). The proposed design permits 24/7 electricity production at the rated power of the turbine practically all year-round. In the hypothesis of no cost penalty for the use of a novel heat transfer and heat storage fluid, and of the higher pressure and temperature of the power cycle, that is a reasonable long term goal of an industrialized and mass-produced solution, the Levelized Cost of electricity may be improved from the 7.29-7.97 ¢/kWh of a current technology 100 MW design of annual average capacity factor 93-95.5%, to the 6.18-6.68 ¢/kWh of a 126 MW design of annual average capacity factor 94.9-97.7% of the novel technology. The work demonstrates the benefits of internal thermal energy storage by molten salt in supplying energy to renewable energy only grid, and the opportunity to further evolve the basic design now employed towards higher temperatures.