Thermal energy storage
Storing energy as heat or cold, in sensible, latent (phase-change) or thermochemical form, for later use as heat or for power generation.
Thermal energy storage (TES) is often the cheapest way to store energy when the end use is heat. Three mechanisms exist:
- Sensible heat: raising the temperature of water, rock, sand, concrete or molten salt
- Latent heat: melting a phase-change material such as paraffin, salt hydrates or ice
- Thermochemical: reversible reactions or sorption, with high density and low losses but low maturity
Water: c_p = 4.186 kJ/(kg·K); 1 m³ heated by 50 K stores 209 MJ ≈ 58 kWh
Solar salt (60% NaNO3 / 40% KNO3): c_p ≈ 1.5 kJ/(kg·K), used 290–565 °C
Ice: latent heat of fusion 334 kJ/kg ≈ 93 Wh/kg
Applications range from domestic hot-water cylinders and electric storage heaters to large pit storage in Danish district heating (Vojens: about 200,000 m³), molten salt tanks giving CSP plants 6–15 hours of storage, and electrically charged sand or brick "heat batteries" supplying industrial process heat.
Seasonal water stores lose some heat over months; well-insulated large stores achieve 60–90% annual efficiency. Combined with heat pumps, TES shifts electricity demand to cheap, high-renewable hours.
Related terms
All terms →- District heating
A network of insulated pipes distributing hot water or steam from central heat sources to many buildings for space heating and hot water.
- Concentrated solar power (CSP)
Power plants that use mirrors to concentrate direct sunlight onto a receiver, heating a fluid that drives a steam turbine, usually with built-in thermal storage.
- Heat pump
A device that uses a refrigeration cycle to move heat from a cooler source (air, ground, water) to a warmer sink, delivering 2–5 units of heat per unit of electricity.
- Long-duration energy storage (LDES)
Storage able to discharge at rated power for roughly 8 hours or more, covering multi-day lulls and seasonal imbalances that 2–4 hour batteries cannot.
- Solar thermal collector
A device that absorbs sunlight and transfers the heat to a fluid, mainly for domestic hot water, space heating, district heating and industrial process heat.