Geothermal Energy Use, 2015 Country Update for Denmark

The geothermal resources in Denmark are available at relatively low temperatures suitable for heat production while electricity production is not possible with the present technologies. Both shallow and deep geothermal resources are used in Denmark. Denmark has three geothermal plants with deep wells producing heat for district heating. Other projects are at different levels of maturation. The first geothermal plant started production in Thisted 1984 and now has a capacity of 7 MWt from 43°C saline water from a Gassum reservoir at 1.25 km depth. A plant in Copenhagen at 14 MWt from 74°C saline water at 2.6 km depth started production in 2005 from a Bunter Sandstone reservoir and the latest plant at up to 12 MWt from 48°C saline Gassum water at 1.2 km depth started production in Sonderborg in 2013. The plants have one production and one injection well producing heat from the sandstone reservoirs through heat exchangers and/or LiBr based absorption heat pumps, where the driving heat primarily comes from biomass boilers for heat and / or combined heat and power production. Shallow geothermal is mainly used for domestic heating via arrays of closed loops in about 1 m depth in combination with heat pumps. Closed loop boreholes to around 150 m depth are also beginning to be used for domestic heating, both for single houses, for smaller collective networks and for heating of larger office buildings. Borehole Thermal Energy Storage (BTES) for seasonal storage of heat is applied in a test plant at the district heating network in Braedstrup. Few installations use a groundwater aquifer for heating, cooling or seasonal storage (Aquifer Thermal Energy Storage, ATES). The number of smaller ground source heat pumps extracting shallow geothermal heat has been assessed to be around 27,000.