Geothermal energy in the UK: The life-cycle environmental impacts of electricity production from the United Downs Deep Geothermal Power project

Abstract

The UK is rich in heat-producing granites, especially in the county of Cornwall, suggesting the potential for energy production with low environmental footprint. The United Downs Deep Geothermal Power (UDDGP) project aims to demonstrate the technical and commercial viability to produce electricity from the Cornish geothermal resource, exploiting the natural permeability of a significant deep structural fracture zone known as the Porthtowan Fault Zone. Drilling of the first well started at the end of 2018, and the plant is expected to be operational by mid-2020. A relevant question is whether deep geothermal energy is truly environmentally benign. This article presents a comprehensive and detailed Life Cycle Assessment study that i) identifies the main life-cycle sources of environmental impacts for the production of electricity in the UDDGP plant; ii) investigates the effects on the environmental impacts of significant uncertainties surrounding the project, such as availability of geothermal fluid and configuration of the power plant, and iii) compares the performance of the UDDGP operation, and by extension of the putative geothermal energy production in the UK, with other key energy sources in the country. The life cycle inventory relies on a combination of site-specific data for wells construction and literature data for above-surface facilities and stimulation techniques. We validated our model by comparing climate change impacts of UDDGP with those reported by other studies on enhanced geothermal systems. Our results show that the greatest portion of environmental impacts originates from the construction phase (primarily due to steel for wells casing and diesel used during drilling), whilst the scenario analysis demonstrates that increasing installed capacity and cogenerating heat and power are the most effective strategies for improving the environmental performance. Our analysis also suggests that the environmental impacts may increase by ∼35% if stimulation techniques are required to increase the geothermal wells productivity. Compared to alternative energy sources, in the category climate change, UDDGP performs better than solar energy and is comparable with wind and nuclear. It is shown that the environmental benefits of geothermal energy are not straightforward and that a number of trade-offs needs to be considered when other impact categories are quantified.