Thermal energy storage
Thermal energy storage saves heat or cold for later use. It can shift heating, cooling, and power demand across hours, days, or seasons using water tanks, rocks, molten salts, phase change materials, underground storage, or thermochemical reactions.
What thermal energy storage is
Thermal energy storage, often shortened to TES, stores useful heat or cold so it can be used later. Instead of storing electricity directly, a TES system stores temperature, phase change, or reaction potential. That stored thermal energy can then heat buildings, cool air, run industrial processes, or help generate electricity.
Sensible heat storage
Sensible heat storage raises or lowers the temperature of a material without changing its phase. Hot water tanks, chilled water tanks, rocks, sand, concrete, and molten salts can all store sensible heat. The amount stored depends on mass, heat capacity, and the temperature difference the system can safely use.
Latent heat storage
Latent heat storage uses phase change, such as melting and freezing. Ice storage systems can make ice when electricity is cheaper or cleaner, then melt it later to cool buildings. Other phase change materials are selected to melt and solidify near useful temperatures for buildings, vehicles, or industrial equipment.
Thermochemical storage
Thermochemical storage uses reversible chemical reactions or adsorption processes. Energy is stored when heat drives a reaction or separates materials, then released when the materials recombine. These systems can have high energy density and low standing losses, but they are often more complex than water, rock, or salt storage.
Buildings and cooling
In buildings, thermal storage can shift heating or cooling away from peak demand hours. Chilled water or ice can support air conditioning after being charged overnight. Hot water tanks, building mass, and phase change materials can shift heat demand and help heat pumps run when electricity is cheaper or cleaner.
District heat and seasons
Large thermal stores can support district heating by saving waste heat, solar thermal heat, or heat-pump output for later. Some systems store heat seasonally in pits, boreholes, aquifers, or large water tanks, charging during warm or low-cost periods and discharging during cold months.
Solar thermal power
Concentrating solar power plants can use mirrors to heat a transfer fluid and store heat in molten salt tanks. When electricity is needed, the stored heat produces steam or drives a power cycle. This lets some solar thermal plants generate after sunset or during passing clouds.
Power and industry
Thermal storage can also help high-temperature industry and electric grids. Concepts such as heated particles, bricks, rocks, or pumped thermal electricity storage aim to store low-cost electricity as heat, then use it directly for industrial processes or convert part of it back to electricity.
Why it matters
Thermal energy storage is valuable because much energy demand is thermal. Heating and cooling buildings, water, and industrial materials does not always require a battery. Storing heat or cold can reduce peaks, use renewable electricity more flexibly, cut fuel use, and make energy systems more resilient.