Life cycle assessment of geothermal plants targeting the lower carboniferous limestone reservoir in northern Belgium

Abstract

The majority of heating in Belgium and Europe originates from natural gas. Deep geothermal heating (DGH) can provide a low carbon alternative to fossil-fired heating. However, the site-specific geological conditions are determinant for DGH development, requiring in-depth assessments to fully understand the potential environmental impacts. This study presents a comprehensive environmental assessment of DGH in Northern Belgium, where growing interest in DGH is observed. Based on an already developed DGH plant, three scenarios are defined depicting current and future DGH developments in Northern Belgium. Twelve Life Cycle Assessment (LCA) impact indicators and the inter-connected geo-technical aspects are investigated. An LCA on the three scenarios is performed, followed by a detailed hotspot analysis. Also, the impact variability is estimated with global sensitivity analysis, followed by variance-based global sensitivity analysis to assess this variability. The global warming (GW) impact of the already developed DGH plant is relatively low (27 kg CO2-eq/MWhth) and is driven (>80%) by the electricity consumed to run the pumps and the well development. The GW impact is lower for the expected future DGH development (11 kg CO2-eq/MWhth) because of shallower reservoir conditions and better permeability that lead to lower pumping needs. A wide impact variability is found, governed (>80%) by the plant capacity, capacity factor and pumping needs. The GW impact ranges from 4 to 130 kg CO2-eq/MWhth. Utilization of DGH in Northern Belgium can lead to a decarbonized heating mix. The environmental impacts of DGH can be reduced by exploiting shallower reservoirs with better permeability to reduce the impacts of well development and the pumping needs of the plant and by supplying the plant with renewable energy sources.