What are the fuels with the highest energy

Questions and answers about synthetic fuels

Emission-free traveling with the combustion engine? So-called e-fuels promise exactly that. But do they keep their promise? Questions and answers about synthetic fuels.


The Paris climate protection agreement requires global warming to be limited to a maximum of two degrees compared to the beginning of industrialization, if possible even to 1.5 degrees. To achieve this, fossil CO₂ emissions from transport must be reduced to almost zero over the next three decades. A CO2-Neutral combustion engine can help. A much discussed solution are synthetic fuels, so-called e-fuels. What can these fuels do? You can read about the advantages and disadvantages of synthetic fuels in our Questions + Answers.

01/01/2020 | In focus | Issue 1/2020

Potential of synthetic fuels

Synthetic fuels will be indispensable in the future. Only they promise the high energy density that is required in shipping, air traffic and heavy-duty logistics, for example. Battery electric drives will probably never be able to do this in a similar form.

  • How are synthetic fuels made?

E-fuels are produced exclusively with renewable energies by initially producing hydrogen from water. This requires large amounts of electricity. Carbon is still required for a liquid fuel. This can be obtained from industrial processes or with filters from the air. This turns the greenhouse gas into a raw material. From CO2 and H2 the synthetic fuel is then obtained - i.e. petrol, diesel, gas or even kerosene. A cycle is created: The CO₂ that is produced and emitted when e-fuels are burned can, so to speak, be recycled and used for the production of new e-fuels. The terms power-to-X (PtX), power-to-liquid (PtL) or power-to-gas (PtG) have established themselves for these processes.

  • What environmental contribution can e-fuels make?

Vehicles powered by synthetic fuel are climate-neutral on the road. In 2017, Bosch experts calculated how big the contribution to limiting global warming would be in Europe's passenger car fleet alone: ​​By 2050, the consistent use of synthetic fuels in addition to electrification could generate up to 2,800,000,000,000 kilograms of CO2 (= 2.8 gigatons). That corresponds to three times the amount of carbon dioxide emissions from Germany in 2016.

In addition, synthetic fuels can be designed in such a way that they burn practically soot-free. Ideally, they are always made up of similar, so-called C1 molecules, and burn almost completely and therefore almost emission-free, explains Wolfgang Maus in the interview "Vehicles should be able to clean the air" from MTZ 1/2016. The requirements for exhaust gas aftertreatment systems and thus also the costs for such systems could decrease.

Scientists at the Institute for Energy and Environmental Research Heidelberg (ifeu) come to the following conclusion in a current study for the Federal Environment Agency (UBA): Greenhouse gases can be saved with PtX energy sources, but even with 100 percent electricity from renewable sources, the production is more synthetic Fuels are associated with considerable environmental pollution. The construction of the wind and photovoltaic systems, the synthesis facilities and the transport infrastructure requires raw materials and is associated with emissions into the air and water. The carbon required for the production of hydrocarbons must be used as CO2 can be obtained from exhaust gases, the air or biomass. This in turn resulted in environmental pollution.

  • Is it worth developing synthetic fuels?

Although electric cars will become significantly cheaper in the next few years, the development of fuels could be worthwhile. In 2017, Bosch calculated that, depending on the cost of the regenerative energy used, a hybrid powered by e-fuels with a maximum mileage of 160,000 kilometers could be cheaper than a long-distance electric car. In addition, the existing filling station network can continue to be used. This also applies to the existing know-how in combustion technology. E-fuels do not differ in their chemical structure and their basic properties from conventional diesel or petrol made from petroleum. They can also be mixed with conventional fuel. Therefore, they work directly in the existing structure. With e-fuels it is also possible to store large amounts of renewable energy and also to transport it worldwide.

An important argument against synthetic fuels: the low level of efficiency. Instead of driving cars directly with green electricity, this is first used to produce hydrogen and then the fuel. A study by the Berlin think tank Agora Verkehrswende from 2017 calculated: The highest overall efficiency is achieved for the battery-powered electric car at 69 percent, followed by the fuel cell vehicle at 26 percent. The least efficient is the car with the use of synthetic fuels in the combustion engine, which ends up with an overall efficiency of 13 percent. In other words: "For the same distance, a car with a combustion engine needs around five times as much renewable electricity as a battery-powered electric car," says Agora Verkehrswende. However, if the electricity comes from more distant regions, i.e. outside of Germany, and must first be converted into a chemical energy carrier for transport and then reconverted into electricity, the efficiency of an electric car in the compact class also falls, as Bosch calculates, to 20 to 25 percent.

Dietmar Goericke believes that we are "beyond the point of the efficiency discussion," said the FVV managing director in an interview of the same name.

If we assume that we are CO2- need neutral fuel, regardless of the form, whether liquid or gaseous, and we can manufacture, transport and store it efficiently, it almost doesn't matter whether the vehicle consumes half a liter more or less. CO2 is in focus. Everyone's Overall Balance ".

Dr. David Bothe, Associate Director at Frontier Economics agrees with him in an interview: Physical conversion losses in the various energy chains are only one aspect and not the decisive one. In a CO2-neutral world, efficiency is no longer decisive, but much more, what is more economical, i.e. cheaper in the overall system. Many analyzes would show that conversion losses can be compensated for by using existing infrastructures, logistics and storage options.

  • Will e-fuels catch on?

Great efforts are still required for synthetic fuels to gain broad acceptance. The system technology is still expensive today and there are only a few test systems such as in Norway. At the moment, "no large-scale PtX system is in planning because the legislation currently does not yet have any CO2- Recognizes reduction through e-fuels. Therefore, market players do not yet see a sufficient business case to invest in e-fuel production ", explain engineers from FEV in the article Carbon-neutral transport - the role of synthetic fuels from the ATZextra special issue for the IAA 2019. Ways to make synthetic fuels more attractive make a tax on CO2 or carbon from fossil sources or the offsetting of carbon-neutral fuels towards fleet emissions through a certificate system.

Many experts see the field of application of e-fuels not in the passenger car, but in the transport sector due to their poor efficiency. In other words, where neither hydrogen nor the direct use of electricity work according to current knowledge: for example in ships, airplanes and parts of heavy goods traffic. Synthetic fuels in cars, on the other hand, could be a solution for the transition between fossil fuels and e-mobility, in order to start off with as much CO as possible2 to save. A current research project of the Karlsruhe Institute of Technology (KIT) is trying to increase the efficiency in the production chain for synthetic fuels. According to the KIT, an efficiency of up to 60 percent is theoretically possible. It remains to be seen whether this value can also be achieved in practice.

  • How expensive will the fuel be?

The production of synthetic fuels is still complex and expensive. But a market ramp-up in production as well as a favorable price development in the electricity price could ensure that synthetically produced fuels become significantly cheaper, predicts Bosch in 2017. In the long term, pure fuel costs of 1.20 to 1.40 euros per liter can be realized by 2030 (excluding tax), by 2050 only costs around one euro. In its study "Sustainable Fuels for Logistics", the Deutsche Post DHL Group identified a mass market potential for synthetic fuels in five to ten years.

  • What is the difference between e-fuels and biofuels?

In contrast to biofuels, with synthetic fuels there is no trade-off between tank and plate. With renewable electricity, e-fuels can also be produced without the amount of biofuels to be expected - for example through limited cultivation areas. In his report Potentials of synthetic fuels from the MTZ 1-2020, Frank Urbansky comes to the conclusion that renewable fuels are generally the only way to "make fuel requirements in logistics, shipping and air traffic more climate-neutral". However, bio-based fuels are now more practicable than e-fuels. "The technologies are more diverse, most of them tried and tested, and fuels that are cheaper than e-fuels can be produced," said Urbansky. However, there is still a lack of research for both renewable fuel sources, and even more, according to Urbansky, "but there is a lack of political will so that they can even be brought onto the market in usable quantities."