Thermal Energy Storage (TES) describes various technologies that temporarily store energy by heating or cooling various storage mediums for later reuse. Sometimes called ‘heat batteries,’ TES technologies work to decouple the availability of heat generated from renewable electricity, solar thermal energy, or even recovered waste heat from when it is actively needed, helping decarbonize industrial processes and the heating or cooling of buildings.

TES is a promising electrification strategy: Because TES can utilize low-cost renewable electricity – for example wind generated in the middle of the night – to produce and store heat for later use, TES provides utility-scale grid storage and helps manage renewables’ intermittency.

Similarly, TES can store heat captured by concentrating solar systems during the day for use during non-daylight hours.

There are various forms of TES technologies that are largely distinguished in terms of the energy sources they draw from, storage mediums they use, and the chemical or physical processes that underlie them. Most commonly, TES technologies store energy in liquids or solids via temperature changes without changing their state of matter. This process often involves converting renewable electricity to heat through common processes such as electrical resistance and storing heat for immediate or later use. Storage mediums include water tanks, molten salt, and materials such as volcanic rock, minerals, ceramic, or concrete. Other forms of TES technologies similarly draw on renewable electricity but store heat via changes in states of matter (e.g. freezing water), often for low-temperature applications in buildings, while other forms of TES technologies work via chemical reactions or by manipulating physical properties of fluids.

TES technologies have strong potential for cross-sectoral decarbonization, especially for heating and cooling buildings and providing heat for industrial processes. TES technologies can provide high temperature industrial heat (above 1,000°C) at extremely high efficiency using common materials that can store heat over long durations. Their cost-effectiveness is expected to further improve over the course of the decade, dropping by about 30 percent for industrial applications by 2030, according to the International Renewable Energy Agency. RTC sponsors Antora Energy, Brenmiller Energy, and Rondo Energy are active in the industrial and institutional spaces, with projects including a cement plant, a major plastics company, and a college campus.