The combination of scientific/technological advances and evolving changes in the power industry provide opportunity to develop large-scale thermal energy storage technology. Engineers used small-scale thermal energy storage during the latter 19th century to provide propulsion for steam-powered submarines that stored saturated water at some 100-psia and 328F (164C) in on-board accumulators. Some early railway shunting locomotives carried tanks of saturated water to supply steam to provide short-distance propulsion in the shunting yards.

During the latter 20th century, various underground geological formations were adapted for seasonal low-grade thermal energy storage, to provide heating and cooling inside buildings. A recent advance in this technology in Alberta, Canada uses solar thermal collectors to achieve seasonal geothermal energy storage at a temperature of up to 80C (176F), to provide winter heating for a community. While parabolic troughs may collect solar thermal energy at some locations, purpose built solar thermal salt ponds may achieve the same task at lower cost at other locations.

The combination of a multitude of exhausted oil/gas wells and extensive strata of porous rock saturated with ground water enhances prospects for such storage at multiple locations across the USA and Western Canada. During winter, temperatures may drop to -40C (-40F) at several northern locations. The temperature difference between the cold winter air and stored subterranean heat at 80C can sustain the operation an Organic Rankine-Cycle (ORC) engine. The size and extent of the thermal storage reservoir would determine the output (Mw-hrs) of such an engine driving electrical generating equipment.

Salt caverns that occur near ground surface are unable to hold natural gas or compressed air at high pressure. There may be scope to hydrate the rock salt and use it for seasonal thermal energy storage at temperatures of up to 150C (300F). Large subterranean thermal storage reservoirs may provide heat for buildings, energize banks of ORC engines and/or thermal chimney engines that flow air through turbines. Stored thermal energy may also sustain the wintertime operation of multi-level greenhouses that use up to 80% less water than conventional outdoor agriculture.

Caverns that contain massive volumes of saline groundwater close to ground surface near large urban centers may serve as a seasonal heat sink, due to the freezing point of saline water being below that of pure water. During the cold winter months, the atmosphere may serve as the heat sink to cool the saline water. During summer, the cooled saline water may sustain viable district cooling of large buildings and reduce electrical energy demand required for air conditioning.