Development of Solid Particle Thermal Energy Storage for Concentrating Solar Power Plants that Use Fluidized Bed Technology

The National Renewable Energy Laboratory is developing a thermal energy storage (TES) system that uses solid particles as the storage medium for a concentrating solar power plant. This paper focuses on the particle-TES performance in terms of three efficiency metrics: first-law efficiency, second-law efficiency, and storage effectiveness. The paper presents the derivation of the efficiency expression and their application in assessing the particle-TES performance and design. The particle-TES system uses low-cost stable materials that withstand high temperature at a fraction of the cost of the salt and metal containment vessels for high-temperature TES. Cost analysis indicates that particle TES costs less than $10/kWhth, which is less than half the cost of the current molten-salt-based TES and just a fraction of liquid heat transfer fluid storage at a similar high temperature of >700 °C, due to its low cost of storage medium and containment. The fluidized-bed TES can hold hot particles of > 800 °C with >95% exergetic efficiency, storage effectiveness, and thermal efficiency.