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System for separating carbon dioxide from the air: gigantic amounts of energy required
Photo: Gaetan Bally / KEYSTONE / picture alliance
General Motors, Ford, Jaguar: a growing number of automakers are saying goodbye to the internal combustion engine in the years to come.
The signs in the industry point to electrics and batteries.
Or not?
In any case, the Association of the Automotive Industry (VDA) holds against it: Combustion engines are also climate-friendly if they are operated with so-called e-fuels.
These synthetic fuels are made from hydrogen and carbon dioxide.
If the hydrogen is produced with green electricity, the fuel is CO2-neutral, argues the association.
According to this logic, the car manufacturers would have every reason to hold on to the lucrative business with gasoline and diesel vehicles for longer.
The association finds open ears in politics.
For example, the federal government recently decided that fuel manufacturers may have the e-fuels they sell for road traffic offset twice against the prescribed reduction in their CO2 emissions.
In order to ensure that enough green hydrogen is available for e-fuels and other applications, for example in industry, in the medium and long term, the federal government adopted the National Hydrogen Strategy last year.
The situation is different with the second ingredient in e-fuels, carbon dioxide: where it should come from is still completely open - although it depends on whether the fuel is of any use to the climate.
"It is astonishing that politicians and environmental associations have so far almost completely ignored the question of possible CO2 sources for synthetic fuels," says Oliver Geden, climate protection expert at the Science and Politics Foundation.
Carbon dioxide from power plants
Obviously, the required CO2 would be obtained from the exhaust air of fossil power plants and industrial plants.
There it is in high concentration.
The technology is well established, the carbon dioxide in lemonades and beer often comes from there.
However, the CO2 obtained in this way is not climate-friendly because it is of fossil origin.
The emissions are only shifted from the chimney to the exhaust - a zero-sum game.
In any case, this source will gradually dry up with the switch to renewable energies.
If the resulting CO2 is used for synthetic fuels, the departure from fossil fuels could be delayed - counterproductive for climate protection.
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"If you install a system for using carbon dioxide in a coal-fired power station or a fossil industrial process, the operators naturally want to use it for as long as possible," says Daniel Münter from the Institute for Energy and Environmental Research Heidelberg Ifeu.
"This means that the fossil fuel plants may run longer than they should, just to be able to generate CO2."
Biomass as a climate-neutral source
These problems can be avoided if the CO2 is obtained from biomass cogeneration plants.
Biogas plants that produce methane for the gas network would also be a possible source.
"If the carbon dioxide comes from biomass, combustion engines only emit as much CO2 as the plants previously took from the air," says Münter.
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However, the potential is limited as there are only a few plants of this type.
Their number could be increased.
But that would create new problems.
Because in order to produce the necessary biomass, you need large cultivation areas and fertilizer, which in turn causes greenhouse gas emissions.
And then there is the tank instead of plate problem: the production of biomass competes with food production.
CO2 filter for the air
More promising is a technology that separates CO2 from the air: so-called direct air capture systems guide a flow of air through a filter, which releases the carbon dioxide it contains.
Prototypes of this technology, for example from the Swiss company Climeworks, are available near Zurich and Iceland, among others.
They show that this concept works well.
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However, the CO2 obtained in this way would serve climate protection even more if it were not blown back into the air via the exhaust pipe, but instead pressed into layers of rock that bind it permanently.
In this way, some of the greenhouse gas emissions could be reversed.
It is possible that the CO2 concentration in the atmosphere could even be reduced again one day in this way.
According to a special report by the Intergovernmental Panel on Climate Change (IPCC), such so-called negative emissions are indispensable for achieving global climate goals.
»If the CO2 from the direct air capture systems is used for synthetic fuels, it is missing in order to achieve negative emissions.
So we have a conflict of objectives, «says Oliver Geden, who was one of the lead authors who worked on the IPCC special report.
E-fuels for aircraft and ships only
Nonetheless, Direct Air Capture is considered to be the most climate-friendly way to generate carbon dioxide for synthetic fuels.
However, the process consumes a lot of energy.
It is only greenhouse gas-neutral if the electricity required comes from solar, wind energy or hydropower plants.
The need for green electricity is even greater, however, for the production of the other ingredient in synthetic fuels, hydrogen.
"If we wanted to replace all fossil fuels in road traffic with e-fuels in this country, this would require at least 2.5 times as much electricity as we consume in Germany today," calculates Ifeu expert Münter.
It is therefore clear to him: "We should primarily use synthetic fuels where there is no alternative, that is, in air and ship traffic - and electrify road traffic."
In the case of cars, the signs are clearly pointing to farewell to the combustion engine.
Even if parts of the auto industry are still vocal about it.
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