Seasonal Thermal Store

Seasonal Thermal Store

Seasonal thermal energy storage (or STES) is the common umbrella term for several technologies for storing heat or cold for periods for up to several months. The uncommon term inter-seasonal thermal storage is a better descriptor, because the thermal energy can be collected whenever it is available and be used whenever needed, even in the opposing season. For example, heat from solar collectors or waste heat or air conditioning equipment can be gathered in hot months for space heating use anytime needed, including during winter months. Waste heat from industrial process can similarly be stored and be used much later. Or the natural cold of winter air can be stored for summertime air conditioning. STES stores can serve district heating systems, as well as single buildings or complexes.

An example of one of the several kinds of STES storages illustrates well the capability of interseasonal heat storage. At Alberta, Canada’s Drake Landing Solar Community (in operation since 2007), the homes get 97% of their year-round heat from a district heat system that is supplied by solar heat from solar-thermal panels on the garage roofs. This feat – a world record – is enabled by interseasonal heat storage in a large mass of native rock that is under a central park. The thermal exchange occurs via a cluster of 144 boreholes, drilled 37 metres into the earth. Each borehole is 155 mm in diameter and contains a simple heat exchanger made of small diameter plastic pipe, through which water is circulated. No heat pumps are involved, although they are often used in conjunction with STES storages.