When the Sun Disappeared: How a Solar Eclipse and Heatwave Sent European Power Prices Above €500

Heatwave simultaneously crushed other supply sources

Extreme temperatures constrained French nuclear output because high river-water temperatures limited cooling capacity, and suppressed German wind generation as calm conditions settled in . Spot prices had already jumped more than 20% in the days preceding the eclipse . The heatwave also reduced the efficiency of combined-cycle gas turbines (CCGTs), meaning even fast-ramping backup plants were not operating at full capacity .

Cooling demand spiked

The heatwave drove up electricity use for air conditioning and refrigeration, compounding the supply squeeze . Day-ahead prices had already surged 21.8% in France to €142.5/MWh and 22.8% in Germany to €138.5/MWh by August 11 .

The result: a near-perfect supply-demand pincer

Less solar + less nuclear + less wind + more demand created a shortfall that wholesale markets resolved at extreme prices. Fast-ramping backup (gas turbines) was already stretched by the prolonged heatwave conditions .

What this reveals about grid vulnerability

Solar dependency creates acute timing risk

Europe has added massive solar capacity in recent years, but when an eclipse knocks it out during a narrow, high-demand window, the system needs rapid substitutes. The fact that prices briefly doubled in 15 minutes shows how thin the slack is during such events . The eclipse's timing — during the evening ramp when solar output is already falling — was particularly unforgiving.

Extreme heat compounds renewable intermittency

Heatwaves do not just raise demand for cooling. They also degrade nuclear output (through thermal discharge limits on river water used for cooling), reduce gas turbine efficiency, and can coincide with low wind speeds . This means the usual