An Energy Systems Perspective on the Life Cycle Assessment of Geothermal Heating Networks

The lifespan of new geothermal heating infrastructure can be expected to extend beyond mid-century, likely coinciding with major transitions in the composition of electricity supply to meet greenhouse gas (GHG) targets. However, despite growing interest in the life cycle assessment (LCA) of geothermal heating, there is a lack of knowledge about the environmental impacts associated with geothermal applications with district heating networks powered by large-scale renewable electricity. We thus extend a previouslypublished LCA study for geothermal heating networks in the State of Geneva, Switzerland. We assess eight environmental impacts for three geothermal design alternatives combining different layouts of district heating network and geothermal extraction temperatures, and for a reference ground-source heat pump (GSHP). We use global sensitivity analysis and scenario discovery to evaluate impacts under uncertainty for eight electricity supply sources, including renewables and fossil fuels. We find that electricity supply source is typically the dominant source of uncertainty in LCA and may lead to trade-offs between impacts: while solar photovoltaic and biomass have low GHG emissions, they respectively lead to the highest water consumption and land use. When compared with GSHP, the relative environmental performance of geothermal heating networks strongly depends on interactions between design parameters of the geothermal network, as well as other energy system properties. Furthermore, different electricity supply technologies may be preferable for different geothermal design configurations. The design of geothermal heating networks should thus account for existing electricity supply, as well as plausible future changes over the lifetime of the system