Thermodynamic analysis of low-temperature fossil-fuel-dependent geothermal energy in the Netherlands

A new regulation by the Dutch government indicates that no natural gas will be supplied to the new building, and the residential heating systems will be gradually replaced by the electricity-driven heat pumps or geothermal heat. The ultimate goal is to supply the total required electricity from the renewable (wind and solar) resources to make the heating systems low-carbon emission. However, the current electricity supply is a combination of fossil fuel power plants (more than 80%) and wind, solar, and nuclear. This means that the overall heat extraction process is not yet fully independent of the fossil fuel usage, and therefore not carbon-neutral. Our objective is to compare the current natural gas heating systems which comprise the majority of residential heating systems in the Netherlands, with the emerging low-temperature geothermal extraction processes and geothermal heat pumps in terms of fossil fuel consumption and total CO2 emission. We analyze the energy and exergy balance of these processes and quantify their CO2 emission. Since the success of a geothermal energy extraction project depends on the quality of the aquifers, we model the underground nonisothermal flow of water in different geologies (porosity and permeability) based on the geological map of the Netherlands to realistically quantify the electricity requirements in the circulation pumps and the total extracted heat. Our results reveal that depending on the permeability of the aquifers, a low-temperature geothermal energy system might be environmentally beneficial (for permeabilities higher than 0.1 Darcy) with a CO2 emission that is lower than the current natural gas heaters. However, for most of the resources with lower permeability, the geothermal energy system has a higher CO2 emission and fossil fuel consumption per unit heat delivered. We finally show the electricity production scenarios which makes the geothermal-based heating systems more environmentally friendly than the natural gas heating systems.