A Comparative Cost and Performance Analysis of Structured and Packed-Bed Thermocline Thermal Energy Storage Systems

Integrated thermal energy storage (TES) is necessary for concentrating solar power (CSP) plants to be implemented as a cost-competitive and reliable power production option. This work presents and discusses existing utility scale CSP plants with integrated TES. The current standard TES system configuration, indirect two-tank, is presented, and the single-tank thermocline is proposed as a cost-reducing alternative. The traditional thermocline concept involves storing energy in a “packed-bed” of solid aggregate; however, concerns exist that settlement of aggregate over repeated thermal cycles may lead to thermal ratcheting and rupture of the tank’s walls. To address this issue, a structured thermocline is proposed, in which the aggregate bed is replaced with plates of concrete. Finite-difference-based numeric models are introduced and used to study the performance of packed-bed and structured thermoclines. A complete cost analysis of a 2,165 MWh_t TES system, considering both thermocline configurations, is provided. System Advisory Model (SAM) is used to perform life-cycle cost and performance analysis of a central receiver CSP plant incorporating three unique TES configurations: none, packed-bed thermocline, and structured thermocline. Conclusions are drawn as to which TES configuration is the most viable.