In 2023, the share of offshore wind power from the North Sea fell for the first time to 13% in Germany, from 17% in 2022, TenneT said.
Netherlands-owned TenneT operates the Dutch high-voltage grid and part of the German grid, and is key in the energy transition away from fossil fuels.
"The 'lost years' are now increasingly having an impact on the 'wind harvest' in the North Sea," TenneT Chief Operating Officer Tim Meyerjuergens said, referring to years of wind power capacity expansion on land.
Meyerjuergens said large wind farms in the North Sea were increasingly having to be curtailed due to bottlenecks in the onshore power grid.
As the installed capacity of offshore turbines is smaller compared to onshore turbines, those in the North Sea are more severely affected by such curtailments.
The German government is still planning to buy TenneT's business in Germany but the plan hit a hurdle after the country's constitutional court ruled that unused COVID-19 pandemic funds could not be utilized for climate projects.