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District heating pipelines at the Datteln IV coal-fired power plant: utilities have to find new ways to decarbonise their district heating
Photo: Jochen Tack / imago images
Munich's hottest candidate for climate-neutral heating is around 3,000 meters below the city: a huge reservoir of hot water.
The local municipal utilities are now tapping into this in order to supply tens of thousands of citizens in the Bavarian capital with heat - the company is building Germany's largest deep geothermal system.
So far, district heating in Munich has mainly come from natural gas and coal - as in many other cities.
Nationwide, around two thirds of the heat in the networks comes from fossil fuels.
Renewable energies contribute just under 18 percent.
In the case of electricity, on the other hand, the eco share is already around 50 percent.
This dominance of natural gas and coal in district heating has a significant impact on the climate balance of the Federal Republic of Germany.
After all, almost six million households in this country are heated in this way.
»Suppliers must increase the share of renewable energies and waste heat in district heating to around 45 percent by the end of this decade.
Otherwise the goal of climate neutrality cannot be achieved, ”says Matthias Sandrock from the Hamburg Institute, a consulting firm specializing in the energy sector.
So far, renewable energy district heating has come almost exclusively from biomass - from wood chips, for example, which are burned in heating plants, or from organic waste in waste incineration plants.
However, biomass is only available to a limited extent.
In addition, researchers criticize that burning wood does more harm than good to climate protection.
Therefore, the utilities have to find other ways to decarbonise their district heating.
There is no magic formula for this.
"Which technologies make sense depends above all on which heat sources are available on site," says Dietrich Schmidt from the Fraunhofer Institute for Energy Economics and Energy System Technology IEE.
Little electricity, a lot of heat
The heat that is contained in local waters, in the ground or in the drainage of sewage treatment plants comes into question.
Large heat pumps bring them to the required temperature level.
The heat pumps need electricity for this.
They use this as a lever: With one kilowatt hour of electricity, they generate several kilowatt hours of heat.
According to Schmidt, a very attractive source of energy for heat pumps is waste heat from industry and commerce.
"There is an enormous amount of unused waste heat in the low temperature range in this country," explains the Fraunhofer researcher.
If heat pumps use such sources, they work particularly efficiently because they have to provide less temperature lift, says Schmidt.
District heating can also be generated with the sun: large solar thermal systems installed in the open field absorb the heat and feed it into the grid.
This is already happening, for example, in Ludwigsburg and Kornwestheim, in Senftenberg or soon in Greifswald.
However, such projects require a lot of space.
The facility in Senftenberg takes up the area of three soccer fields.
In addition, solar thermal has the disadvantage that it generates the least amount of heat in winter - that is, when most of it is needed.
Deep geothermal energy does not have this problem.
The systems provide a lot of heat even when it is bitterly cold outside.
For geological reasons, this form of heat generation is not possible everywhere in Germany.
Renewable district heating with higher costs
Solar thermal and deep geothermal systems as well as heat pumps together currently account for less than one percent of total district heating generation.
This is mainly due to the cost.
"Generating district heating with renewable energies is more expensive under today's framework conditions than with natural gas or coal," says Sandrock.
The federal government knows this too - and is therefore planning extensive financial support with the “Federal Funding for Efficient Heating Networks” (BEW).
"If the BEW comes as the government has signaled, it would be very attractive for district heating suppliers," explains Sandrock.
He speaks in the subjunctive because the funding guidelines have been waiting for more than a year.
A spokeswoman for the responsible Federal Ministry of Economics justified the delay on request with the fact that the funding touches on questions of state aid law.
Therefore one is in coordination with the EU Commission.
The aim is to pass the directive by the end of June, said the spokeswoman.
The price of electricity has to go down
According to Sandrock, federal funding alone is not enough.
In his opinion, politicians should also make electricity cheaper so that heat pumps would become financially more attractive.
This is likely to happen in the next legislative period, as there is broad consensus across all parties on this issue.
If politicians set the right course, the climate-friendly conversion of district heating to the suppliers will not fail, Sandrock is convinced. »The industry has recognized the need to replace fossil fuels in district heating with renewable ones. A lot will happen in the next few years. "
