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Workers at a gas turbine from Siemens: "The specifications for converting gas-fired power plants to hydrogen make investments in new plants more complicated"
Photo: IPON / IMAGO
Get off the gas as quickly as possible: Whether for reasons of climate protection or because of the war in Ukraine - there are several reasons to want to get away from fossil fuels.
At the same time, numerous new gas-fired power plants will have to be built over the next few years as a safety net for renewable energies.
They should step in when wind turbines and solar systems are weak.
How does that fit together?
The solution is hydrogen.
Because the plants should not use natural gas, but green hydrogen, at least in the medium to long term.
The fuel is climate-neutral because it is produced from water by electrolysis using green electricity.
However, hydrogen has completely different combustion properties than natural gas.
The power plant turbines available on the market today are overwhelmed by this.
In addition, it is far from clear where the green fuel will come from.
Suppliers fear that this could slow down the expansion of gas-fired power plants – and thus slow down the energy transition.
duty to convert
Gas-fired power plants with an output of a good 30 gigawatts are currently connected to the grid in Germany.
A total of 13 gigawatts must be added by 2030, as calculated by the think tank Agora Energiewende.
Other institutes even see a much greater need.
In order to provide an incentive for investments in new plants, the EU recently classified gas-fired power plants as climate-friendly in its taxonomy.
This should make it easier for utilities to finance the construction.
However, to ensure that no fossil ruins are created, the taxonomy stipulates that from 2036 onwards only CO2-neutral gases such as green hydrogen may be used in the plants.
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The federal government also wants to set requirements for the suppliers.
The cabinet has passed a draft law according to which new gas-fired power plants that generate heat as well as electricity will only receive funding if they can be converted to hydrogen from 2028.
Higher investment costs
But there are still no gas turbines on the market that can be operated with hydrogen.
"During talks with power plant manufacturers, we received feedback that hydrogen-capable gas power plants should be ready for the market by around 2030," explains Johannes Wagner from the Energy Economics Institute at the University of Cologne (EWI).
In order to ensure that enough new power plants are built in this decade, the EU taxonomy allows natural gas turbines to be installed there first.
However, by 2036 at the latest, these must be replaced by ones that can handle 100 percent hydrogen.
According to Ingbert Liebing, General Manager of the VKU Association of Public Utilities, a later change of fuel causes considerable additional costs - not only for the turbine replacement.
The periphery must also be prepared for operation with hydrogen from the outset.
"The supply lines, for example, have to be much larger because hydrogen has a much lower volume-specific energy density than natural gas," explains Liebing.
This also means, among other things, that the turbine hall has to be built larger.
Supply of green hydrogen not secured
"The requirements for converting gas-fired power plants to hydrogen make investments in new plants more complicated," confirms energy market expert Wagner.
And he points out another hurdle: "Anyone who is building a new gas power plant now must be sure that there will be enough green hydrogen available at the site," says Wagner.
»But this certainty does not yet exist.«
After all, the energy source is a coveted commodity, and industry and transport will also need large quantities of green hydrogen in the future.
In addition, a pipeline network must first be created through which the fuel can reach the power plants.
Public utilities are holding back
But the legal framework of the energy market also stands in the way of the construction of new plants, according to the suppliers.
He does not offer enough security that the construction of gas power plants will be profitable in the long term.
"We are currently seeing a very difficult situation when it comes to financing investments in gas-fired power plants and gas-fired combined heat and power plants," says VKU boss Liebing.
"As a result, the municipal utilities are currently reluctant to build new plants, although a massive increase in guaranteed capacity is urgently required."
This means there is a risk that by 2030 there will not be as many gas-fired power plants available as are necessary to ensure a secure supply.
In this case, individual coal-fired power plants would probably have to remain connected to the grid longer - a setback for the energy transition and climate protection, since they emit far more CO2 than gas-fired power plants.
Higher combustion temperatures
But why can't the turbines designed for natural gas run on hydrogen?
This is because the combustion behavior of the two gases differs greatly, explains Christian Fleing from the German Aerospace Center (DLR).
"The density, combustion temperature and flame speed of natural gas and hydrogen differ enormously," explains the expert.
When using hydrogen in a natural gas turbine, for example, it could happen that flames from the combustion chamber flash back into the burner itself.
"That quickly leads to material failure," says Fleing.
Researchers from science and industry, including from DLR, are therefore working on developing burner technologies and geometries designed for hydrogen.
On the other hand, it is technically not quite as challenging to convert gas-fired power plants in such a way that they can cope with a small admixture of hydrogen to the natural gas used.
A joint pilot project by three utilities and Siemens Energy in a power plant in Vienna will show how this concept works in practice.
Such projects are good for climate protection: According to the project partners, even with 15 percent green hydrogen in the fuel gas, around 33,000 tons of CO2 could be saved annually in the Vienna power plant.
However, this does not solve the problem of building new plants.