Storage for renewables and flexibility through standardized use of building mass

The increasing penetration of variable renewable energy and the electrification of heating and cooling create a growing need for distributed energy flexibility and storage. IEA Energy Storage TCP Task 43, *Storage for Renewables and Flexibility through Standardized Use of Building Mass*, investigated how thermally activated building systems (TABS) can exploit structural building mass as a controllable thermal energy storage resource and support their widespread international deployment. The Task addressed four interconnected areas covering construction and materials, system integration and control, non-technical and market conditions, and standardization and performance indicators.

The results show that TABS are technically mature and can provide low-temperature heating and cooling while simultaneously functioning as distributed thermal storage. Market-ready and refurbishment-oriented solutions demonstrate the feasibility of extending thermal activation beyond conventional slabs to walls, façades, and modular building elements. Large-scale deployment, however, requires industrialized and standardized construction, validated material and component data, storage-aware operation, suitable flexibility metrics, and interoperable digital interfaces. Control approaches can range from robust rule-based strategies to forecast-driven and optimization-based operation depending on the intended flexibility service, while thermal comfort remains a fundamental boundary condition.

The principal barriers to further uptake are increasingly non-technical rather than technological. Fragmented regulation, insufficient time-resolved incentives, limited aggregation opportunities, unclear value streams, and constraints on data access prevent much of the available flexibility from being activated. Task 43 therefore recommends combining productization and prefabrication with simplified state-of-charge and performance assessment methods, secure digital integration, appropriate market access, and regulatory recognition of building-mass flexibility. Overall, the Task establishes TABS as a mature pathway for transforming buildings from passive energy consumers into flexible thermal storage assets capable of supporting renewable-rich and increasingly electrified energy systems.