CO2 as feedstock for the production of renewable fuels
Solar and wind energy are competitive technology options for the electricity and heating sector. The conversion of water and CO2 to synthetic fuels now opens the opportunity to use these renewable energy sources to power the aviation sector. Our system analyses of renewable synthetic fuels1–3 reveal that the provision of the feedstock CO2 is much more cost-intensive than the provision of water. The CO2 source is also a decisive parameter for the sustainability of the fuel path.
Synthetic fuels can only be sustainable if the emissions from their combustion are balanced by prior carbon capture, thus preventing further accumulation of atmospheric CO2. In the context of carbon capture and utilisation, it is debated whether a favourable CO2 balance can also be achieved by utilising flue gases from fossil power plants. In case of Power-to-Liquid (PtL) fuels, it is easy to show that the renewable electricity use significantly exceeds specific electricity generation in the power plant. The largest existing CO2 source is therefore not suitable for sustainable fuel production.
Some fuel projects may be located near bio-methane or bioethanol plants, which are already among the most cost-effective sources of CO2. This also eliminates the costly transport of CO2. However, covering the entire aviation fuel demand with synthetic fuels will probably require CO2 extraction from the atmosphere. First pilot plants for direct air capture exist, but considerable development effort is needed to establish the required production capacities. In the long term, Bauhaus Luftfahrt projects a cost contribution of 20 to 30 cents per litre of fuel for direct CO2 air capture.
1 Falter, C.; Batteiger, V.; Sizmann, A. Climate Impact and Economic Feasibility of Solar Thermochemical Jet Fuel Production. Environ. Sci. Technol. 2016, 50 (1), 470–477; DOI 10.1021/acs.est.5b03515.
2 SUN to LIQUID public report: Technoeconomic and environmental analysis of CO2 provision from various sources; Bauhaus Luftfahrt: Taufkirchen, Germany, 2018.
3 Schmidt, P.; Batteiger, V.; Roth, A.; Weindorf, W.; Raksha, T. Power-to-Liquids as Renewable Fuel Option for Aviation: A Review. Chem. Ing. Tech. 2018, 90 (1–2), 127–140; DOI 10.1002/cite.201700129.
- System comparison for PtL: CO2 supply from the air (top) and from a power plant (bottom). The carbon cycle is only closed for direct air capture. CO2 provision from coal power plants is unsustainable due to the very unfavourable energy balance.
- Contribution of CO2 provision to the fuel costs: CO2 supply from ethanol plants currently costs about 10 euros per tonne of CO2; the long-term costs of direct air capture may be slightly below 100 euros per tonne of CO2.