Synthetic fuels are hydrocarbons obtained in the laboratory by combining the basic elements carbon and hydrogen. Carbon is extracted from carbon dioxide present in the atmosphere, while hydrogen comes from the electrolysis of water using electricity produced from renewable sources. For this reason they are also called e-fuel or power-to-liquid. They can replace petrol, diesel and kerosene while maintaining compatibility with current engines and infrastructures. Let's see how the process happens.
Production of synthetic fuels
What synthetic fuels can you get? Not only liquid fuels, but also gaseous ones such as methane and LPG. The synthesis occurs starting from the basic elements, so it is possible to recreate most of the hydrocarbons used today in transport.
Production process.
In short, CO2 is extracted from the air, hydrogen is produced through electrolysis and these elements are combined together in special reactors that simulate the geological formation of oil. However, the technical details are not trivial and the systems require a large availability of renewable electricity.
Neutrality with respect to CO2 emissions.
If the entire process takes place with clean energy, in the end there is a neutral emissions balance: the CO2 released during combustion is the same used to produce the e-fuel. In theory, therefore, these fuels are carbon neutral.
Use in current engines
Compatibility with internal combustion engines. The tests carried out so far confirm full compatibility with today's engines. Only minor adjustments to fuel systems, such as in filters, are necessary. Mixed with traditional petrol and diesel they still reduce CO2 emissions.
Differences compared to biofuels. Both types recycle CO2 already present in the atmosphere, however biofuels derive from crops that compete energetically with human nutrition. E-fuels overcome this environmental problem thanks to chemical synthesis.
Advantages and disadvantages
Advantages of e-fuels
They use current distribution infrastructures, have high energy density ideal for air transport, combustion is cleaner than with fossil fuels. They can also store surplus renewable electricity production.
Problems and limits
They require large amounts of green electricity, the systems are expensive, the extraction of CO2 from the air is inefficient and complex. Furthermore, there is a high water consumption to produce the hydrogen necessary for the synthesis.
Comparison with electric vehicles
CO2 emissions.
Despite being carbon neutral, the production process of e-fuels and the low efficiency of thermal engines limit their climate benefit. Electric cars, despite having no tailpipe emissions, remain more efficient throughout their entire life cycle.
Efficiency and energy consumption.
A well-to-wheel efficiency of 10% is estimated for e-fuels compared to 70-80% for battery-powered vehicles. In practice, over 20 kWh of electricity are needed to produce 1 liter of 10 kWh synthetic fuel. A decidedly less than rational use of available renewable energy.
Economic and environmental feasibility
Production costs.
Currently e-fuels cost over 4 euros per liter to produce. It is difficult to compete with traditional petrol and diesel without heavy public subsidies. Prices may drop in the future, but will remain well above fossil fuels.
Overall sustainability.
The gigantic quantity of green electricity needed to replace the entire car fleet with synthetic fuels appears difficult to find. Not to mention the massive energy waste inherent in the synthesis process and use in internal combustion engines.
In conclusion, synthetic fuels represent a partial escape route for petrol and diesel engines in sectors that are difficult to electrify in the short term, such as aviation. However, for cars their widespread use appears unsustainable and less efficient than electric traction. Therefore, it is better to focus decisively on battery-powered mobility for private and commercial road transport. With all due respect to internal combustion engines.
