Ultra-High Temperature Thermal Energy Storage. Part 1: Concepts

Renewable energy sourced from the sun, wind, waves or tides is clean and secure. Unfortunately, the energy that can be extracted from renewables and the demand for it varies both temporally and spatially. Therefore, energy storage is required to match generation with use. To date grid-scale energy storage has been limited by low energy densities, long-term performance degradation, low round-trip efficiencies or limited deployment locations. Although thermal storage has found uses these have been restricted to lower temperatures by thermal losses resulting in low energy densities and uneconomical electricity generation efficiency. In this paper an ultra-high temperature (1800K) storage system is proposed where heat losses are minimised and recovered to make a higher storage temperature attractive, thus unlocking greater energy densities and efficiencies. Radiation dominates heat losses at ultra-high temperatures but can be minimised through the design of the storage medium container. However, even after energy is lost from storage, heat pumps in the store and charge cycles in addition to preheating during the extraction cycle can be used to recover a significant amount of heat. Collectively loss reduction and recovery techniques can lead to a storage system with a performance and utility that exceeds other energy storage methods. Here the feasibility of the novel storage technique is demonstrated through thermodynamic and thermal analysis in each of the three key states of operation: charge, store and generation.