Buildings have a significant untapped potential for demand response through their energy flexibility. This flexibility primarily relies on various energy storage methods, such as electric batteries or water tanks, along with dispatchable on-site energy supply and services. Additionally, the thermal inertia of indoor spaces offers substantial energy storage capacity, easily harnessed through temperature setpoint adjustments. 

While this approach shows promise for building demand response, estimates of large-scale capacity remain scarce. This article provides an estimate of Denmark's building stock's heat storage capacity, comparable to that of combined batteries in large electric vehicle fleets or industrial-scale storage tanks in district heating plants. Utilising building stock as a thermal storage resource could greatly benefit grids at minimal cost.

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