Simplified Parameterized Models for a Multi-Criteria Environmental Impact Assessment of Four Types of Geothermal Installations

Abstract

Life cycle assessment (LCA) is a standardized, multi-criteria environmental assessment methodology for products or systems over their entire life cycles. Applying LCA to energy systems provides a robust basis to fully grasp their environmental performances but is data-intensive, time-consuming, and requires expert knowledge to handle all methodological aspects. As a result, the potential of LCA to support decision-making on new energy systems development is not exploited to its fullest. Alternatives to detailed LCAs, such as simplified models, are increasingly relevant and currently available to estimate the global warming potential of wind energy and enhanced geothermal systems (EGS) for electricity generation. These simplified models are deduced from comprehensive reference parameterized LCA models by identifying a number of key parameters using variance-based global sensitivity analysis. Their development and use are however rare and models for the multi-criteria assessment of other energy generating pathways are lacking. In this paper, we present simplified models for the environmental assessment of four geothermal installation types: (1) EGS for heat generation with very low direct emissions, (2) geothermal flash power plant producing electricity and a limited amount of heat from a geothermal source with moderate to high content of non-condensable gases (mostly CO2), (3) combined heat and power geothermal plant with low direct emissions, and (4) heat production plant including a demonstration organic Rankine cycle producing electricity for self-consumption with very low direct emissions. For each geothermal installation type, seven simplified models were developed to estimate impacts on climate change, minerals and metals resource depletion, fossil resource depletion, human toxicity carcinogenic and non-carcinogenic effects, freshwater ecotoxicity, and freshwater and terrestrial acidification using only two to six installation-specific parameters. Applying these simplified models is useful to give quick and reliable first estimates of the life-cycle related environmental impacts of installations that fall into the applicability domain of the considered model.