The Azimuth Project
Thermal energy storage (Rev #5, changes)

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To have page that lists and compares Thermal Energy Storage (TES) systems and processes. Wikipedia defines it as:

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 reseroir 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 or process water heating.


TES is a generic term for several different storage technologies and depending on the source it can be designed as underground TES (UTES) either in the for of Aquifier TES (ATES) or Borehole TES (BTES). Deep lake water cooling (DLWC) - utilizing the constant temperature of 4 degrees C in areas with cold winters or if its thermal energy from the sun we have Solar TES (STES or SES).

It also uses several different materials as phase change material (PCM). As examples of deployed or investigated materials are: water, inorganic PCM like salts and salt hydrates, organic PCM as paraffins, sugar alcohol and fatty acids. Also combinations of inorganic and organic materials have been investigated, see Paksoy et. al pp 261-265 for details. There are over 50 commercially available PCM’s today.

Deep lake water cooling

It has been deployed at Cornell University, USA in a a project called Lake Source Cooling that started in 2000 and has enabled cooling savings up to 80%.

Underground thermal energy storage

UTES can be deployed and typically its decided which technology to use depending on the geophysical conditions of the place. ATES uses aquifiers - water carrying layers below groundwater level:


For the BTES you need several parallel boreholes 50-200 m deep: