The German Minister for Education and Research Professor Johanna Wanka spoke recently at the inauguration of a power-to-liquid plant in Dresden: “This method reduces CO2 emissions and thus makes us less dependent on crude oil. In this way, we can protect our climate, save resources, and at the same time promote a technology that promises economic growth. Furthermore, the biggest advantage of power-to-liquid fuels is that the entire infrastructure of already existing gas stations, pipelines and engines can be used without any adjustments. This means that we are facilitating a sustainable mobility with renewable energies.”
At the event, the German company sunfire GmbH demonstrated a technology that produces synthetic gasoline from carbon dioxide (CO2) and water, using electricity from renewable sources to power the process. This event was just one in a series of recent developments in the field of ‘Power-to-Liquid’ (PtL) and ‘Power-to-Gas’ (PtL), with new projects coming online in Germany and abroad. The core concept is the combination of CO2 with renewable power to produce sustainable synthetic fuels. This could provide energy carriers that are easy to integrate and have the potential to cut CO2 emissions and reduce our dependency on fossil fuels. The possible implications of this approach for the transition to a more sustainable energy system are increasingly being discussed, notably at the Energiewende Research Forum. What role could synthetic fuels play? And what are the risks and uncertainties associated with them?
A practical solution to satisfy our fuel needs
The rationale for synthetic fuels arises from the need to reduce the use of fossil hydrocarbons and their associated GHG emissions, while ensuring an energy supply that meets the requirements of a modern society. Currrently, fossil fuels and their derived products are ubiquitous: they power car, ship and plane engines, they provide heat and electricity, and they are used as feedstock in the petrochemical industry.
The popularity of fossil fuels – especially liquid fuels – stems from a few key characteristics: high energy density per unit of mass combined with ease of storage, transportation and distribution. A whole infrastructure exists to accommodate them, and many economic and industrial structures rely on them. Given the powerful inertia that creates, the task of introducing alternative energy carriers that would require a completely different system could prove to be daunting, at least in the medium term.
Conversely, with PtL and PtG, all of these fuels could theoretically be produced synthetically, from recycled CO2. As the CO2 emitted during fuel combustion is offset by the amount used in the synthesis process, net emissions could be greatly reduced. As such, PtL and PtG schemes are part of the galaxy of mitigation measures subsumed under the term Carbon Capture and Utilization, whose overarching goal is to ‘close the carbon cycle’.
Complementarity with renewable energy sources
Synthetic fuels can only be truly carbon-neutral if their production process is powered by renewable energy from sources like wind and solar. In a way therefore, they allow renewable electricity to be ‘stored’ in liquid and gaseous fuels, which are a much more efficient and convenient energy-storage medium than, for instance, batteries.
Since renewables are naturally intermittent, i.e. the power output fluctuates based on the availability of sun and wind, the possibility of buffering this intermittency through PtL and PtG conversions is an interesting option. For this reason, synthetic fuels are often promoted as a way to facilitate greater penetration of renewable energy sources.
Taking all this into account, recent studies in Germany have looked into long-term scenarios relying on renewable electricity and synthetic fuels. They conclude that such schemes would be technically feasible and would lead to large reductions in CO2 emissions.
Beyond technology: synthetic fuels as part of a wider transformation process
Despite these promising features, there are still a number of uncertainties and unresolved issues. First of all: where should the required carbon input – such as CO2 – come from? Some countries, like some Nordic countries for instance, plan to use biomass extensively. But this may not be an option everywhere due to the limited availability of biomass. In future, it might be possible to rely on direct atmospheric capture of CO2, thereby enabling
a closed carbon cycle; this, however, depends on a number of technologies reaching appropriate levels of technical maturity and cost-efficiency.
The obvious solution, at least for the time being, is to capture the CO2 emitted by gas and coal power plants using Carbon Capture (CC) techniques. This would of course provide sufficient inputs of carbon for producing synthetic fuels, but it might raise other issues. Firstly, it assumes that the market for CO2 would be sufficiently developed for plant operators to adopt costly CC systems. But more importantly, there are concerns that this could reinforce fossil fuel path dependencies. The end goal is to phase out fossils altogether. But if we associate synthetic fuels with the current fossil industrial chain, wouldn’t that only strengthen it, provide arguments for keeping fossil fuels, and interfere with the main message of the energy transition? Or would it just be a practical way of cutting emissions now rather than later without jeopardizing long-term goals?
In short, the technology for sustainable synthetic fuels already exists; but the wider conditions for their implementation, and the social, economic and political ramifications of that are not well understood. Much also depends on whether PtL/PtG schemes would be pursued as a sort of intermediary ‘bridge’ solution, as an end in itself, or just as one option in a wider portfolio of mitigation measures.
The issues of technical feasibility are dwarfed by these more important questions: the energy transition represents not just a switch to different technologies, but also an economic and societal transformation. In this respect, it is still unclear how synthetic fuels could fit in this process. The fact that these discussions have recently been attracting more attention might help to broaden the scope of the debate and open the way to a more comprehensive assessment of the potential of sustainable fuels.
Pictures (c) sunfire GmbH