Solar Water Heater boiler by Gerard Mourits

An advantage of using groundwater is the constant temperature throughout the year, which is unlike other heat sources, such as outside air or a ground heat-exchanger system. 

Using the ground as a seasonal thermal energy store is referred to as underground thermal energy storage. Aquifer Thermal Energy (ATE) is a source of renewable energy that is very much increasing around the world. It involves pumping a relatively large amount of groundwater, and raising and lowering the temperature, usually by small amounts. 

Currently, aquifer thermal energy storage projects are largely designed to store cold energy in winter for cooling purposes in summer time. In most cases the stored chilled water is utilized directly to cool. Chiiler or heat pumps are utilized only for supplementary purposes during peak conditions. It is also possible when heat pumps are included that they can be used for heating purposes in the winter. In this case it is referred to as 'cold storage and low temperature heat storage.