Thermal storage comprises of a number of technologies that store thermal energy in energy storage reservoirs for later use.

They can be employed to balance energy demand between day time and night time.

The thermal reservoir may be maintained at a temperature above (hotter) or below (colder) that of the ambient environment. The applications today include the production of ice, chilled water, or eutectic solution at night, or hot water which is then used to cool / heat environments during the day.

Thermal energy is often accumulated from active solar collector or more often combined heat and power plants, and transferred to insulated repositories for use later in various applications, such as space heating, domestic hot water or process water heating.