High Quality Content by WIKIPEDIA articles! Thermal energy storage comprises 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.