The France-Germany day-ahead power spread flipped direction three sessions running: on 14 July Germany was dearer by EUR 6, a day later France took the dearer leg by the same EUR 6, and by 16 July Germany led again by EUR 3 1. This is the price gap between the two grids' next-day electricity, and it did all of that with the same block of French nuclear frozen offline throughout , so no restart can explain the swings.
The spread normally reads as a proxy for French nuclear: when EDF's fleet runs cheap, France clears below Germany and exports across the interconnector. The curtailment risk EDF flagged on 9 July has now overwhelmed that mechanism entirely. With a single heat dome sitting over both countries at once, the spread stops pricing supply and starts pricing which nation's air-conditioning load tops out first: French cooling demand outran a short fleet on 15 July, German heat pulled its own price up faster on 16 July.
Cross-border traders positioned for France-cheaper on the expected restart got whipsawed session to session, and interconnector flow direction now turns on which grid's demand peaks first rather than on generation. The spread reverts to its old logic only when the reactors come back and one grid regains a structural supply edge over the other.
