Deep geothermal energy extraction, a review on environmental hotspots with focus on geo-technical site conditions

Knowledge about the environmental impacts of geothermal energy is important for understanding the role this technology could play in the transition towards sustainable energy production systems. In this study 30 life cycle assessment (LCA) studies on geothermal energy plants were reviewed, focusing on the major environmental hotspots and the cause-effect relationships between the geo-technical parameters and these environmental impacts. The variability in the reported environmental impacts is explained, and a more transparent picture of the geological, design and technical factors causing these impacts is provided by triangularly evaluating the reported results based on the plant's geo-technical characteristics (such as, well depth and geofluid temperature), the life cycle inventory, and the hotspot analysis results. The study focuses on six impact indicators that have been identified as high priority for geothermal energy by the GEOENVI project, as well as the water consumption impact. The results indicate that the impacts vary in magnitude and across different life cycle phases. Apart from the type of energy conversion technology used, differences in the geological and design parameters also introduce large variability in the impact results reported in the literature. Furthermore, all the reviewed LCAs adopt a static approach. Therefore, we present a research agenda that highlights the need to perform dynamic LCAs on geothermal energy exploitation plants to consider the changing context in which these technologies are operating. •Environmental impacts of geothermal energy extraction vary strongly.•Factors determining the impacts vary for different energy conversion technologies.•Site-specific geo-technical parameters drive the environmental impacts.•Dynamic assessment is required to accurately estimate impacts in time.