Techno-economic assessment of seasonal heat storage in district heating with thermochemical materials

Highlights: • Identification of suitable thermochemical materials for seasonal heat storage. • Determination of expectable heat generation costs for different use cases. • Coverage of base load is identified as preferable use case. • Hydration-based materials perform best combined with industrial resources. • Heat generation costs are significantly higher than considered benchmarks. -- Abstract: Thermochemical energy storage provides opportunities for pressure-less and low-loss seasonal storage at high energy densities. For that purpose, appropriate storage concepts are drafted and examined in technical, ecological and economic terms, considering suitable materials, energy sources, and charge and discharge reactor concepts. The results illustrate that the choice of the district heating grid to be supplied, the locations of the energy sources for charging, and the transfer distance have major influence on the potential use cases for thermochemical storage (TCS) materials. Grids with a high number of full load hours and low power demand (base load coverage) are much better suited to this type of heat storage compared to peak load applications, allowing the high fixed material costs and investment to be recouped. The use of hydration-based TCS materials (hydrates and hydroxides) is particularly suitable if costs for material transport and supply of the required water vapor can be avoided. Thus, with industrial waste heat as a low cost energy source, heat production costs around 100 €/MWh could be achieved. For larger spatial distances between the energy source and the grid, metallic TCS materials are favourable due to higher storage densities. Major costs in the heat recovery of redox materials are those for the electrical energy needed for reduction, resulting in total costs well above 120 €/MWh. In all cases investigated, the calculated heat production costs for thermochemical storage are significantly above those of conventional district heating applications. This paper supports a pre-selection of relevant TCS materials and applications in district heating for future detailed analysis.