Five and Six

While France saw nearly 70,000 households lose electricity during the heatwave, Luxembourg kept the lights on. Grid load increased by only 5 to 6% during the hottest days, a remarkably modest figure given that temperatures approached 40°C and air conditioning units were running at full capacity across the country.[1]

The explanation, according to Marc Meyer of Creos, Luxembourg's grid operator, comes down to two factors. First, the country's 36,200 photovoltaic installations generated more power thanks to the abundant sunshine, helping offset the higher demand from cooling. The same weather that stressed the grid also fed it.[1]

Second, Luxembourg's high-voltage grid is designed according to the N-1 criterion: lines are duplicated, so if one fails, the other takes over. This means that under normal conditions, the grid never runs beyond 50% of its capacity. The trade-off is overbuilding. The benefit is resilience. When a heatwave pushes demand up by 5 or 6%, a grid designed to handle double its normal load barely notices.[1]

Creos did make operational adjustments. Outdoor maintenance work was shifted to early morning hours to protect workers from the heat. Customer services, including new connections, continued on normal schedules. The grid operator's proactive approach, combined with the underlying infrastructure design, meant that Luxembourg experienced no overloads and no bottlenecks.[1]

The contrast with neighbouring countries is striking. France, with its older infrastructure and heavy reliance on nuclear power (which also struggles in heat, as river water becomes too warm for cooling), faced significant outages. Luxembourg's combination of distributed solar generation and conservative grid design proved its worth. The question is whether this resilience scales. More heatwaves will come. More air conditioning will be installed. The 5 to 6% increase of 2026 could become 15 or 20% in a few years. The N-1 criterion provides margin, but margins are not infinite.