AleaSoft Energy Forecasting, August 21, 2026. This summer’s heatwaves are simultaneously affecting different European electricity systems, though through different channels. They increase cooling-related electricity demand, constrain generation availability and raise price volatility. The episodes recorded in Spain, France, Italy, Romania and Hungary show why anticipating these risks requires a view across the whole of Europe’s electricity markets.
Extreme heat is no longer an anomaly
Since late June, Spain has recorded several episodes of exceptionally high temperatures. June was the second-warmest in the historical series, with a temperature 3.2°C above average. July recorded an average temperature of 25.7°C, 2.6°C above normal, and was, tied with July 2022, the warmest month on record in Spain, according to AEMET data.
The consequences go far beyond weather records. In early August, the MoMo system run by the Carlos III Health Institute estimated around 3450 deaths attributable to high temperatures since June, with more than 2000 in July alone.
The phenomenon has a European dimension. The World Health Organization considers the 2026 heatwaves a significant public health risk in Europe and warns that extreme episodes are becoming more frequent, intense and prolonged.
One phenomenon, different effects depending on the electricity system
Extreme heat is also testing electricity generation, but its effects depend on the characteristics of each system.
In France, high river water temperatures and, in some cases, low flow rates have forced the adaptation of output at several nuclear power plants over the summer. Reactors at Bugey, Golfech, Tricastin, Chooz and Saint-Alban have reduced output or been temporarily shut down to comply with environmental limits related to the temperature of the water used for cooling.
In south-eastern Europe, the problem has been especially visible on the Danube. In Romania, Nuclearelectrica began the controlled shutdown of unit 2 at the Cernavodă plant on August 13 in response to the significant and continued drop in the river’s level.
In Hungary, the Paks nuclear plant drastically cut its output due to exceptionally low Danube water levels. Authorities adopted extraordinary measures to keep enough water available for cooling and avoid a complete shutdown.
Italy shows another side of the same phenomenon. According to data from TERNA, the Italian system operator, electricity demand reached 32.5 TWh in July, the highest figure on record for that month and 8.3% above July 2025. On July 15, demand also hit its annual peak, at around 58 GW. Terna attributed much of this increase to the exceptionally high temperatures.
More demand, less margin and more volatile prices
When heat simultaneously increases demand and reduces or constrains the availability of certain technologies, the effect can quickly pass through to electricity markets.
In Spain, the average day-ahead market price reached €104.75/MWh in July, 51% higher than in June and 50% higher than in July 2025. On July 23, at the height of the heatwave, the hour between 21:00 and 22:00 exceeded €255/MWh.
Heatwaves often coincide with episodes of weak wind, a phenomenon known as heatflaute. Its effect is especially visible in the late afternoon and early evening, when solar output disappears while cooling demand remains high, amplifying intraday price volatility. The episode on July 23 in Spain, with the 21:00 to 22:00 hour above €255/MWh, follows exactly that pattern.
Heat was not the only factor. Rising gas prices, against a backdrop marked by the crisis in the Strait of Hormuz, also contributed to the price increase.
The pressure was not limited to the Iberian market either. On August 17, the day-ahead price in France reached €177.35/MWh, its highest level of the year to date, while Germany recorded €176.73/MWh, its third-highest price of 2026. The episode occurred in a summer marked by recurring nuclear generation restrictions in France and episodes of low wind production in Germany, two factors that had already pushed up prices on earlier days that same month.
These episodes show that a heatwave can simultaneously alter several elements of the system: demand, generation availability, cross-border energy exchanges and prices.
Heat does not affect all markets equally
Europe’s electricity markets are interconnected, but they do not react in the same way to an episode of extreme temperatures.
The generation mix, the availability of interconnections, demand’s sensitivity to temperature, renewable production, water availability and environmental restrictions determine how the impact is transmitted in each country.
That is why the same episode can translate into a demand record in Italy, nuclear restrictions in France, Romania or Hungary, and sharp price swings in Spain, France or Germany.
Summer heatflaute and its winter equivalent, dunkelflaute, are becoming a recurring challenge for Europe’s electricity system: the weight of weather-dependent renewables is critical when climate patterns become more extreme and harder to predict.
For companies that operate in or have exposure to more than one market, analysing each country in isolation gives an incomplete picture. Developments in one market can affect exchanges, generation availability and prices in neighbouring markets.
Forecasts to anticipate scenarios in European markets
In this context, short and medium-term forecasts make it possible to anticipate how extreme weather episodes can pass through to demand, renewable generation and prices in each market.
AleaBlue, the AleaSoft Energy Forecasting division specialising in short and medium-term forecasts, provides hourly forecasts of these variables for the main European electricity markets.
Using a consistent analytical framework across countries makes it possible to compare markets’ expected evolution and identify where the greatest risks and opportunities may be concentrated, which is especially relevant for traders, energy retailers, generators and large consumers with activity or exposure in different countries.
Anticipation in the face of an increasingly frequent risk
Extreme heat is no longer just a weather phenomenon. It is also a challenge for health, infrastructure and energy systems.
Adaptation requires strengthening grids, energy storage, demand flexibility, interconnections and the resilience of generation facilities, while electrification and decarbonisation continue to advance.
Better forecasting does not prevent a heatwave, but it makes it possible to better prepare electricity systems, businesses and essential services. The more frequent and intense these episodes become, the greater the value of anticipating how they will affect each market and how the different European electricity systems will interact.
Source: AleaSoft Energy Forecasting