Mapping potential sites for shallow geothermal energy and energy storage, -a desktop study from Aarhus (Denmark)
Claus Ditlefsen (GEUS), 22 June 2021
The municipality of Aarhus consists of a large fast-growing urban area surrounded by open land with suburbs and smaller villages. As part of the municipality’s overall climate plan, they are committed to reduce CO2 emissions, e.g. by examining the possibilities to utilize shallow geothermal energy (SGE) and of storing surplus heat in the subsurface. Therefore, the aim of the pilot case study has been to investigate the possibilities to integrate SGE and energy storage in the existing mature central heating system.
A mapping of potential sites for open groundwater based aquifer thermal energy storage (ATES) facilities has been carried out using comprehensive sets of existing geological and geophysical data as well as an existing 3D geological model developed within the national groundwater mapping program.
The approach has been to seek out extensive aquifers (i.e. > 25 acres and thicker than 15 m) with a tentative distance of more than 500 m to existing drinking water wells, figure 1. Furthermore, it has been assessed that within the designated drinking water protection areas only balanced low temperature ATES can safely be operated without potential risk of negative thermal effects on drinking water resources. In each potential area this needs to be evaluated further by hydrothermal modeling of local temperature and groundwater flow.
Outside the designated drinking water protection areas one urban locality has been found that could potentially contain ATES at higher temperatures. However, this also needs to be further evaluated by modeling local temperature and groundwater flow applying a realistic range of storage temperatures in the model.
Likewise, mapping of sites potentially suited for borehole thermal energy storage (BTES) has been conducted using sets of existing geological and geophysical data. For this purpose, areas with limited groundwater flow have been mapped, figure 2. The impermeable Paleogene clays below Aarhus have been recognized as potential formations for BTES systems. To minimize drilling depth and facilitate installation of the closed loop boreholes, areas where the clay is found less than 25 m below the surface have been mapped. In the higher parts of the landscape south of Aarhus City, soundings of the water table indicate the presence of an unsaturated zone that in places are more than 20 m thick. These areas are regarded as potentially suitable for BTES. However, since most of the potential sites are located within water protection areas, further investigations are needed.
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