Dynamic life cycle assessment of geothermal heat production from medium enthalpy hydrothermal resources

Abstract

Geothermal energy is a renewable energy source with large unexploited potential. Medium enthalpy deep geothermal resources are commonly used in Europe to provide heat. Life Cycle Assessment (LCA) studies on such applications are scarce and their majority follows a static approach. We describe a two-step dynamic LCA framework for deep geothermal heating applications to more accurately estimate their environmental performance. A semi-dynamic approach considers the temporal evolution of the processes and a fully-dynamic approach also applies dynamic impact assessment methods. We investigate a deep geothermal heating plant located in Northern Belgium for which site-specific data are available. Compared to a static LCA, the dynamic methods find a 50–129% higher global warming impact. Analogous differences are found for eleven other impacts. Regardless, the global warming impact remains lower than for natural gas heating. Large impact variations are also observed when the average European electricity mix is considered to supply the plant, indicating that LCA studies on pumped geothermal heating plants that neglect the time parameter could be largely misestimating the impacts. The dynamic LCA also calculates the impact evolution through time. We find that the continuation of the plant operation after a time period might not lead to considerable impact reduction. Such information is hidden in a static approach and could be used for the optimization of geothermal development strategies. Dynamic methods also facilitate the design of targeted impact mitigation strategies and the comparison between alternative heating systems. We recommend the application of dynamic LCA on other types of geothermal energy plants and other energy-related applications.