Curtailment of biogas plants: when the wind blows, biogas flares up

The expansion of the power grid in Germany is not keeping pace with the energy transition. This has consequences especially for operators of biogas plants.

A biogas plant in Eilringen, Lower Saxony Photo: Philipp Schulze/dpa

FREIBURG taz | Farmer Jens Soeken counts the hours. For example in January: The farmer from Großefehn in East Friesland had to switch off the biogas plant, with which he supplies electricity and heat, for a total of 213 hours. That’s almost a third of the month. It wasn’t because Soeken ran out of the necessary biomass – for example plants, organic waste or liquid manure – through whose fermentation the gas is produced. Instead, he was curtailed. This is what happens when the grid operator forces the operator of a power plant to switch off in order to prevent the electricity grid from being overloaded.

Their expansion is not keeping pace with the energy transition. In northern Germany in particular, due to the successful construction of wind turbines, there is often too much electricity to be routed via the grid to where it could be consumed. So many farmers feel the same way as Soeken. Your biogas plants are curtailed. In Lower Saxony, the regions of East Frisia, Rotenburg/Wümme and almost all districts on the Bremen-Hanover-Hildesheim-Brunswick axis as well as all coastal regions are particularly affected, according to the Lower Saxony/Bremen State Association for Renewable Energies (LEE).

“It has never been as bad as it has been since mid-December,” says Soeken. In the past, his system only had to be disconnected from the grid during a storm, but today this often happens when the wind is only moderate.

In practical terms, this means that Soeken will be compensated for lost income, but in the meantime gas will continue to be produced in its plant. At some point the memory will be full. Then the farmer has to burn off the unused gas. Particularly bitter: Soeken not only supplies electricity with its biogas power plant, it also supplies some neighbors with heat. If the grid operator shuts down Soeken’s system due to grid bottlenecks, it can no longer supply heat. “Then my neighbors have to switch on their fossil-fired heating systems while I burn off the biogas,” says the farmer.

Too many regulations

In principle, it would be possible to use the biogas in times of excess electricity to generate heat alone. But such a technical upgrade of the plant raises so many approval issues that every farmer keeps their hands off it, says Soeken.

In its monitoring report for 2021, the Federal Network Agency states a curtailed biogas electricity volume of a good 72 million kilowatt hours. Almost all of this is in Schleswig-Holstein and Lower Saxony. According to the authority, almost three quarters of the failure are caused by bottlenecks in the transmission network, which are the large national power lines. The rest comes from insufficient distribution networks that lead directly to the end consumer.

The problem is getting worse: “Recently, curtailments of more than 80 hours have been increasing in Lower Saxony,” says Joost Kuhlenkamp, ​​consultant for bioenergy and heat at LEE Lower Saxony/Bremen. No farmer could keep a memory for such a long shutdown. Usually, the storage is dimensioned in such a way that the farmers can shift their power generation to those hours in the daily rhythm when the power is needed the most. This is also economically attractive for the operators because they generate higher revenues in the hours of scarcity on the electricity market.

The Biogas Association has now proposed a different switch-off sequence. The lobby group wants to give preference to systems that supply heat as well as electricity. As a result, wind turbines would lose out compared to some biogas plants.