The environmental impacts and the carbon intensity of geothermal energy: A case study on the Hellisheiði plant

Abstract

Geothermal energy, alongside other low-carbon and renewable energies, is set to play a key role in decarbonising the power generation industry to meet the Paris Agreement goal. Thus far the majority of Life Cycle Assessment (LCA) studies focused on enhanced geothermal plants. However, conventional geothermal plants that harness hydrothermal reservoirs dominate the production of electricity from geothermal energy worldwide. This article focuses on Hellisheiði, a combined heat and power double flash geothermal plant located in Iceland, with an installed capacity of 303.3 MW of electricity and 133 MW of hot water. The study has a twofold goal: (i) identify hot spots in the life cycle and, where possible, suggest improvements, and (ii) understand the potential of geothermal energy to decarbonise the power generation industry. First, a detailed LCA study has been performed on Hellisheiði, with cradle-to-grave system boundaries and detailed site-specific data obtained from the literature. The analysis identifies consumption of diesel for drilling and use of steel for wells casing and construction of the power plant as the main hot spots. Second, carbon intensities of electricity production for various possible configurations of the Hellisheiði power plant (including single flash, and power-only production) have been compared with those of other geothermal plants and other energy sources. Different allocation procedures have been used to allocate impacts between electricity and hot water where necessary, and Monte Carlo simulations have been used to estimate uncertainties of Hellisheiði's carbon intensities. The comparison shows that the carbon intensity of Hellisheiði is in the range of 15-24 g CO₂-eq./kWh, which is similar to those of binary cycle geothermal plants, solar (photovoltaic) and hydropower, lower than other geothermal technologies and fossil-based technologies, and higher than nuclear and onshore wind.

Keywords: Carbon intensity; Environmental impacts; Geothermal energy; Life Cycle Assessment; Uncertainty analysis.