The UK on the brink of a blackout
Temperatures reached 35.8°C in West Sussex, shattering the all-time June temperature record for the United Kingdom. With demand up 6.4% and combined-cycle gas turbine (CCGT) plants experiencing 40% more unplanned outages due to reduced air density limiting turbine combustion, NESO secured 1.7 GW of import capacity via submarine interconnectors with continental Europe. To do so, the operator agreed to pay approximately €1,652/MWh (£1,400/MWh), roughly 20 times the average market price of June 2025. The UK’s thermal and gas capacity fell by 2.5 GW at the peak of the crisis.
France, despite its own constraints, was called upon as an emergency supplier. Its exports fell to 3 GW compared to 12 GW under normal conditions, hampered by a 4.1 GW reduction in nuclear capacity due to thermal restrictions on its rivers. The French spot price reached a daily peak of €268/MWh, while demand rose 5.1%.
Spain torn between a solar record and a wind drought
In Spain, where temperatures were forecast to approach 44°C in Córdoba, the situation took a paradoxical turn. The country recorded its highest solar photovoltaic output for a June day. However, the blocking anticyclone known as the Omega Block paralyzed wind production: on June 16, output fell to 43 GWh, its lowest level in three years. The Ascó and Vandellós nuclear reactors maintained production at 100% capacity, their respective hydraulic configurations shielding them from temperature constraints on the Ebro. The Spanish spot price crossed the €100/MWh threshold.
The anticyclone also struck Italy, which recorded the largest increase in electricity demand across Europe according to ENTSO-E (European Network of Transmission System Operators for Electricity) data, surging 12% over a single week. Italian wind production hit a three-year low on June 21 at just 13 GWh. Forced to import heavily from France and Switzerland, the country posted the highest weekly average electricity price in Europe at €127.69/MWh.
Switzerland stabilizes nuclear output through Alpine reservoirs
In Switzerland, MeteoSwiss issued a maximum red heat alert for the cities of Geneva and Zurich. Despite this backdrop, operators Axpo and Alpiq maintained stable nominal output at their Beznau and Gösgen reactors. According to the operators, a synergy with Alpine hydroelectric dams — releasing deep, cold water from high-altitude lakes — lowered the temperature of the Aar River by 0.5°C to 1.2°C upstream of the cooling circuits, neutralizing the heat wave’s impact on downstream waterways.
In Germany, which has no nuclear generation, photovoltaic efficiency losses and net imports in the evening pushed the spot price to €545/MWh, the continental high for the day. German demand rose 1.2% over the period, the smallest increase among Europe’s major markets affected by the heat wave.