ACER Clears Capacity Calculation Rules for Thirteen-Country Core Power Region
ACER's approval of TSO-proposed changes to cross-border capacity methodology covers the EU zone that includes France and Germany, Europe's two largest power markets.
Europe's energy regulator approved changes to cross-border power capacity calculation rules for 13 EU countries on Sunday (2026-07-20), covering day-ahead and long-term timeframes across the Core region, which includes France and Germany, Montel reported.7
German baseload power was trading at €132.45/MWh as of Friday (2026-07-24), reflecting summer supply tightness and the difficulty of moving surplus power across borders when rules constrain available capacity. The new rules govern how transmission headroom is calculated and shared between neighboring bidding zones, directly affecting volumes available in day-ahead and forward auctions.7
ACER — the EU Agency for the Cooperation of Energy Regulators — endorsed changes that transmission system operators across the Core zone had proposed to the methodology for both short-dated and longer-term capacity allocation. The Core region spans markets with sharply different generation mixes, making capacity calculation methodology more consequential than in a homogenous zone.7
France and Germany exemplify that divergence. German grids have absorbed rising renewable volatility: in the first eight months of 2025, Germany ran negative power prices roughly 10% of the time, up from 5% across all of 2024 and just 3% in 2023, according to The Economist. Surplus generation has no place to go when cross-border capacity is constrained or misallocated. France runs a nuclear-heavy baseload that swings sharply during heat events. French nuclear output cuts deepened to 12% of total capacity during the record heatwave that struck Europe in late June (2026-06-26), lifting prices across the region, Montel reported.3,5
At that point, Montel's senior energy analyst Fintan Devenney said power demand was high across Europe, "driven in part by increased cooling load" — the exact conditions under which accurate cross-border capacity signals matter most.6
More battery and interconnector capacity across Germany and France would not resolve the trend of power prices at EUR 3/MWh and below expected through 2030, a study from consultancy Thema found, as reported by Montel. That conclusion points to a limit the revised calculation rules share: they determine how existing transmission headroom is allocated, not how much exists. Europe added a record 8.8 GW-hours of battery storage in 2024, ten times the 2020 figure, yet Michael Waldner, chief executive of Pexapark, told The Economist: "The market is screaming for capacity."1,3
The EU's next seven-year budget proposes raising grid spending to over €30bn, up from €5.8bn in the previous cycle, a signal that the infrastructure gap is acknowledged at the policy level. More than 70 GW of renewable capacity was added across Europe in 2025, led by Germany, Spain and France, according to a Montel study by EnAppSys, EQ and Energy Brainpool analysts — volumes that make cross-border capacity calculation both harder to execute and more valuable when done accurately.3,2
TotalEnergies filed in June (2026-06-01) for authorization on a EUR 4.5bn, 1.5 GW offshore wind project off the Normandy coast, France's largest proposed renewable project. Built out, it would add to the hours when French generation surplus requires efficient cross-border routing — and when the accuracy of capacity calculation has direct price consequences for German buyers.4
Regulatory approval and operational change are not the same event. TSOs must translate the new calculation methodology into actual capacity announcements, and the lag between a methodology shift and its effect on auction-available volumes can span multiple scheduling cycles. German power at €132.45/MWh on Friday (2026-07-24) reflects a market that is not waiting. Whether the revised rules widen or narrow accessible capacity on the French-German border will appear in day-ahead auction results before most participants have had time to model the change.7