Seasonal thermal energy storage: A techno-economic literature review

Seasonal thermal energy storage (STES) holds great promise for storing summer heat for winter use. It allows renewable resources to meet the seasonal heat demand without resorting to fossil-based back up. This paper presents a techno-economic literature review of STES. Six STES technologies are reviewed and an overview of the representative projects is provided. The key project parameters and operation performances, including the main heat source fraction, storage efficiency, and energy density, are investigated in the technical review. The economic viability is assessed in terms of the levelized cost of heat (LCOH), storage volume cost, and storage capacity cost. The results show that the tank and pit thermal energy storage exhibits relatively balanced and better performances in both technical and economic characteristics. Borehole and aquifer thermal energy storage exhibits better economic performance, while latent and thermochemical heat storage exhibits better technical performance. Compared to the reference heating alternatives, i.e., natural gas and solar heating for decentralized systems, only pit and low-temperature aquifer thermal energy storage is economically competitive. The LCOH of latent heat storage is the highest. To be economically competitive in the heating market, the LCOH of STES needs to be reduced by half to four times less. Meanwhile, a decision tree for STES selection is introduced to facilitate practical engineering. In compiling the data for this review, we find that STES economic studies are limited in number and often lack transparency in their reporting. Going forward, this should be improved to provide a more solid base for policymaking