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In Sweden, ground source energy systems, with a number of different configurations, have been used for approximately 40 years. The most common ones are ground coupled heat pumps for energy extraction from vertical boreholes (rock heat) and horizontal coils in the upper soil (topsoil heat). Currently there are some 300 000 of these systems in operation. Also groundwater is commonly used for extraction of heat (groundwater heat) or cold (groundwater cold). In general, the energy from the underground is regarded as a renewable source of energy, and contributes currently with some 10 % of the total space heating in the country. Since these systems preferably replace fossil fuels, they represent a significant reduction of CO2 emission in the country.
In the later two decades, a new generation of systems has been developed and implemented on the market. These systems, underground thermal energy storage (UTES), combine heating and cooling and are preferably used for commercial buildings and institutions. Some large-scale applications can also be found connected to district heating and cooling systems. There are two such concepts that have successfully been implemented on the Swedish energy market, aquifer thermal energy storage (ATES) and borehole thermal energy storage (BTES). In this paper statistic estimates on applications of different systems, factors impacting the market penetration are given, as well as calculations on the reduction of CO2. Furthermore, the conditions for the future use of these systems are addressed.
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