| Abstract |
Geothermal resources have a large potential to be utilized for more than electricity generation and district heating only. Most geothermal power plants have great unused potential in the form of thermal energy of various grades after the geothermal steam has been harnessed for electricity production. Gas emitted from geothermal power plants includes CO2, currently treated as a waste stream that is emitted to the atmosphere, but with the potential to be captured and harnessed as a value stream for various processes. As the emphasis on more efficient utilization of earth’s resources and on CO2 emission reductions increases globally, it is becoming increasingly important and commercially viable to harness these geothermal waste streams and turn them into value. This circular economy approach can benefit both the owners of the geothermal resources and society as a whole. One usage case for geothermal waste streams is the production of renewable fuels. Geothermal areas can be very suitable locations for the production of hydrogen via electrolysis. Such production requires electricity and water, both of which are readily available at most geothermal power plants. In high-temperature electrolysis (solid oxide electrolysis), the water input can be supplied in the form of steam, thereby reducing the need for electrical energy input to the electrolysis process. This is particularly feasible in geothermal areas where excess thermal energy in the form of steam is accessible. The produced hydrogen can be utilized directly, e.g. as a transportation fuel, or used as a raw material for other industrial processes. Geothermal areas can also be very suitable locations for the production of synthetic, sustainably produced hydrocarbon fuels such as methane or methanol. Such fuels can be produced by reacting hydrogen with CO2 that has been captured from the gas emissions of the geothermal area and subsequently purified. Fuels produced in this way, often called electrofuels, can be considered carbon-neutral and can replace fossil fuel usage in e.g. the transportation sector. Electrofuels are foreseen to become a vital component in decarbonizing those mobility applications where direct electrification is not feasible, and here geothermal resources can play a role. Landsvirkjun operates the Krafla geothermal power plant in Iceland, which emits approximately 28 kilotons of CO2 annually. Landsvirkjun has the goal of becoming CO2 neutral by the year 2025, and for realizing this target, renewable fuel production from geothermal resource streams, including CO2, might play a role. This paper provides an overview of the main technological pathways for renewable electrofuel production from geothermal resources and includes a brief case study for potential renewable fuel production at Landsvirkjun’s Krafla geothermal power plant in Iceland. |