Agriport A7 is a large-scale greenhouse area in Middenmeer in the Netherlands. The local energy company ECW provides geothermal heat (92ºC, from 2 km depth) to the greenhouses through a heating network. The geothermal systems have significant overcapacity in the summer period while in winter they can provide only ~25% of the heat demand, resulting in a strong dependence on fossil fuels. ECW has built a full-scale High Temperature Aquifer Thermal Energy Storage (HT-ATES) system, which facilitates the large-scale storage of surplus heat (overcapacity in summer) and its recovery in winter time. HT-ATES improves the yearly net heat production of geothermal systems hence reduces GHG emissions.
The full-scale HT-ATES doublet well system allows the storage of heat in an unconsolidated sand aquifer at nearly 400 m depth, with a maximum flow rate of 150 m3/h. Each summer, up to 28,000 MWh of thermal energy (>100.000 GJ) can be stored, the bulk of which is recovered in winter.
The HT-ATES system is an innovation that takes place at the edge of technology. The depth (360-380 mbgs) and the temperature of 85 degrees Celsius offered technical and legal challenges that had to be overcome. On a technical level, the standardized well design for ‘regular’ ATES systems (< 25 oC, <200 mbgs) needed to be reconsidered entirely. Components of both the well and the surface installations must withstand the combination of high temperatures, saline groundwater and high pressures. Knowledge and experience from both the ATES and Geothermal sector were combined to get to a suitable design.
The reliability of the HT-ATES system finds root in the knowledge and experience available from thousands of lower temperature ATES systems that have been successfully built and operated in the Netherlands over the last decades. Risks identified in former small-scale HT-ATES pilot-projects were investigated within the HEATSTORE context, and the results contribute to the quality of the full-scale HT-ATES system. The test drilling performed in 2019 has offered a detailed image of the subsurface properties and the risks associated with it. A highly detailed system was designed, and successfully installed. Clogging risks are tackled by a special CO2 dosing unit and groundwater will be monitored on chemical and microbial changes.
In the second quarter of 2021, the installation of the HT-ATES has been completed and the system has been taken into operation. During the test period, samples were taken from the groundwater and analysed on the chemical composition and microbiological content. Also temperature profiles were made during the injection of heat into the aquifer. The first results are very promising and gives valuable information about the effects of an HT-ATES on the aquifer and environment.