The good news is: Kerosene can be produced fully synthetically without resorting to crude oil - even in large quantities in the long term.
Synthetic kerosene can only be truly CO2-neutral if only renewable energy is used in the form of electricity from solar and wind power plants.
Jochen Remmert
Airport editor and correspondent Rhein-Main-Süd.
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At this point, there is some less good news, at least for the power-to-liquid technology (PtL), which is currently mentioned particularly often: It takes enormous amounts of such climate-neutral electricity to convert water, carbon dioxide (CO2) and electricity with this technology to produce only the amount of kerosene sold in Germany in a completely CO2-neutral manner. The Frankfurt Center of Competence for Climate, Environment and Noise Protection in Aviation (Cena) calculates in its new study on this topic: In 2018, a good ten million tonnes or around 12.5 billion liters were pumped into aircraft tanks at German airports throughout Germany. Even if it were possible to produce this amount of kerosene from the electricity used without losses, around 125 terawatt hours would be required.
In fact, the experts calculate an energy loss due to the conversion of around 50 percent.
According to this, 250 terawatt hours of green electricity would have to be used to produce the amount of kerosene fueled at German airports in 2018.
In the same year, however, according to the study, only a good 225 terawatt hours of electricity were generated from renewable sources throughout Germany.
According to this, it would not have been possible in 2018, due to insufficient production of green electricity, to even meet the needs of air traffic completely with synthetic kerosene.
Ten times as expensive as conventional kerosene
It should also be borne in mind that the production of PtL kerosene is currently around ten times as expensive as the conventional production of kerosene. However, PtL production is still in the development phase. With a further development up to a regular production, the costs should also decrease. In principle, synthetic, if not climate-neutral, fuel is not a new invention. Synthetic fuel was produced in Germany around 100 years ago - albeit with different processes.
The large amounts of electricity used to produce PtL kerosene are needed to split water into oxygen and hydrogen using electrolysis. To put it simply, the latter is then synthesized with carbon dioxide to form liquid hydrocarbon, which is then further processed into liquid fuel. In principle, this means that not only aircraft can be refueled, but also cars with combustion engines, which is why car manufacturers have been researching synthetic fuels for years. Because apart from climate protection, the end of profitably exploitable oil reserves is foreseeable.
However, the study sees the storage of large amounts of hydrogen as one of the major problems of PtL technology that has yet to be solved.
This is necessary if the market is to be supplied with fuel across the board, which is generated exclusively with electricity from solar and wind energy that is naturally not available around the clock.
The hydrogen then has to be produced in reserve for the time when the wind and sun do not provide any energy.
The storage of hydrogen - liquefied by cooling and compression - is currently common in liquefied gas tanks.
The study continues, however, that these forms of storage are not suitable for large-scale needs because of the space and material requirements.
So there are still a lot of unanswered questions.
Particularly promising process
According to the Frankfurt study, the sun-to-liquid approach is still in the research phase. Sunlight is bundled via parabolic mirrors and, with marginal losses compared to the PtL process from water and CO2, liquid fuel is ultimately obtained. However, the complete dependence on strong and continuous solar radiation makes this form of fuel production appear more suitable for African or at most southern European countries.