In 2026, European power systems faced an unprecedented test, the results of which surprised even the most cautious analysts. Extreme heatwaves and droughts that hit the continent exposed the weakness of conventional thermal power plants in a way not seen for decades. Historically low water levels in rivers such as the Danube and Rhine led to reduced power generation in nuclear plants in Hungary and Romania, while in France, up to 20 percent of nuclear capacity was unavailable at times due to heat and cooling problems.
For decades, thermal power plants, whether coal, gas or nuclear, were considered the backbone of European power systems because they provided stable, dispatchable power that could be relied upon regardless of weather conditions, unlike wind and solar which depend on the weather. However, the summer of 2026 demonstrated that this assumption is no longer valid, since heatwaves and droughts affect the very operation of these plants, particularly those with open-loop cooling systems that draw water from rivers and discharge it back at higher temperatures.
The problem is not limited to a single country or technology, because from Hungary and Romania to France, operators of nuclear and coal-fired plants were forced to reduce output or shut down units entirely due to a lack of sufficient cooling water or excessively high river temperatures, which made it impossible to maintain safe operating parameters. What was once considered a theoretical risk has become a tangible reality that forces system operators to fundamentally rethink their approach to planning and managing generation infrastructure, because the assumptions of the past no longer hold in a rapidly changing climate.
The most spectacular and alarming consequence of this year’s heatwave was the paralysis of nuclear power in Central and Eastern Europe, because the Hungarian Paks nuclear plant, which supplies about half of the country’s electricity demand, had to curtail its output due to record-low water levels in the Danube, from which it draws cooling water. The situation was so critical that Hungarian authorities decided to sink barges in the river to raise the water level and ensure continuous reactor cooling, an unprecedented measure that highlights the severity of the crisis and the desperation of the operators.
In Romania, for the same reason, units at the Cernavoda nuclear plant were taken offline, which further destabilised the regional power system and forced neighbouring countries to increase their own generation or imports to compensate for the shortfall. Insufficient water levels are a problem for any thermal power plant with an open cooling system, regardless of whether it is a gas-fired, coal-fired or nuclear unit, because they all rely on the same basic physical principles of heat exchange that require adequate water flow and temperature.
When drought is combined with multi-day heatwaves that raise river water temperatures, the problem becomes twofold because the parameters of the intake water have a direct impact on cooling efficiency, and high water temperature reduces the ability to dissipate heat, forcing plants to curtail output or shut down completely to avoid exceeding limits for warm water discharge into the environment.
This phenomenon, which just a few years ago was treated as a theoretical risk, has today become a tangible reality that forces power system operators to fundamentally change their approach to planning and managing generation infrastructure because the traditional assumptions about plant availability no longer hold in a warming world. The Hungarian transmission system operator MAVIR, despite requests from the media, did not respond to questions about its preparations and plans for the future, which may indicate the scale of the challenges it faces and the uncertainty surrounding how to address them.
The summer of 2026 has shown that the security of supply in Europe is no longer solely a matter of fuel availability or grid capacity, but also of water availability, which adds a completely new dimension to energy planning that had previously been largely ignored.
French nuclear power under heat pressure. The paradox of an export giant
Although the situation in France was not as dramatic as in Central and Eastern Europe, the heatwave also affected the fleet of nuclear plants along the Loire, because on 12 August 2026, as much as 20 percent of all nuclear capacity was unavailable, which was the result of a combination of scheduled maintenance outages, cooling problems and unusual events such as a plague of jellyfish that clogged the cooling pumps at the Gravelines plant.
Despite these difficulties, France remained a key exporter of electricity in Europe, because in 2025 it broke its export record, sending 92.3 TWh of energy beyond its borders, which is more than half of Poland’s annual consumption and demonstrates the scale of French nuclear capacity even when some units are offline. The French transmission system operator RTE assures that there is no concern about power availability and system operation during this year’s heatwaves, because the infrastructure was designed to cope with extreme weather conditions, and the greater challenge remains winter peaks when heating demand is at its highest.
RTE also has a long-term plan to adapt infrastructure to climate change, as set out in the Strategic Network Development Plan, which assumes the allocation of 24 billion euros by 2040 to modernise the entire system, so that 80 percent of the network will be made resilient to climate change through a combination of reinforcing lines, installing new transformers and implementing advanced monitoring and control systems.
France remains Europe’s electricity storehouse, and its exports bring tangible financial benefits, because in 2025 the value of net electricity exports reached 5.4 billion euros, which is a significant contribution to the French balance of trade and helps to stabilise electricity prices in neighbouring countries. The French experience shows that even a system with a high share of nuclear power, which is generally considered more resilient than fossil fuel plants, is not immune to climate impacts, but with proper planning and investment can maintain its role as a pillar of European energy security.
Germany shows that renewables with storage can stabilise the grid during heatwaves
In Germany, unlike Poland or France, there are as many as four transmission system operators: 50Hertz Transmission, Amprion, Tennet TSO and TransnetBW, all of which assure that both this year’s and previous heatwaves have not led to disruptions that negatively affected network users, despite the country’s massive deployment of variable renewable energy. This is particularly noteworthy given that Germany has over 127 GW of installed solar PV capacity, and at the peak of the heatwave it supplied around 50 GW of power, which accounted for nearly 33-39 percent of demand, demonstrating that solar power can make a major contribution to meeting summer peaks when air conditioning loads are highest.
An analysis by the think tank Ember shows that part of the generation from solar PV was not used immediately, but went into energy storage, of which Germany has 14 GW of capacity, and pumped-storage hydroelectric plants with 10 GW of installed capacity, allowing this reserve to be used later, outside the hours of peak solar generation, which effectively balances the system.
Later, this stored energy was used beyond the hours of peak solar generation, which allowed for effective system balancing, because the shortfalls in solar generation were supplemented, of course, by conventional power plants, mainly gas and coal, as well as imports, which is still necessary in the current phase of the energy transition.
Despite the heatwaves and the challenges posed by such a high share of renewables in the mix, the German power system did not experience major problems in the summer of 2026, which proves that a well-planned and operated system with a high share of renewables can maintain reliability even under extreme conditions. German operators assure that climate change is systematically taken into account in both operations and further development of grid infrastructure, because the risks associated with climate are integrated into the planning, construction, operation and maintenance of the transmission network, which means that new investments are designed with future climate conditions in mind, not just present ones.
Poland in the grip of heat. Record prices and capacity market call-ups
Poland also felt the effects of this year’s heatwaves, although the scale of the problems was different from that in Western or Central and Eastern Europe, because Polish Power Grids again announced a call-up on the capacity market due to heatwaves and decreasing operating reserves, which means that the system was operating closer to its limits than is comfortable for operators. The situation directly translated into a sharp rise in exchange electricity prices, which was felt by both individual consumers and industry, because according to Polish Power Grids data, on 12 August 2026, electricity prices on the day-ahead market reached record levels, hitting 2,500 PLN per MWh during the evening peak hours, which represented an increase of over 300 percent compared to prices at the beginning of the month. This price spike demonstrates the vulnerability of a system that still relies heavily on coal and has limited flexibility and storage capacity to cope with sudden demand surges and generation shortfalls.
Polish conventional power plants, unlike their counterparts in Hungary or Romania, did not report cooling problems, but the pressure on the system was enormous, because high temperatures increased energy consumption by air conditioning, while at the same time limiting the efficiency of some generation units, which created a perfect storm for system operators trying to maintain the balance between supply and demand.
The situation showed that the Polish power system, despite being largely based on coal, is not immune to extreme weather conditions, and the question arises whether Poland is ready for further heatwaves and whether the plans for modernising the grid and developing new generation sources take into account the new climate realities. The experiences of other countries show that investments in energy storage and system flexibility are crucial for ensuring supply stability in the face of climate change, because they allow excess renewable generation to be stored during periods of low demand and used when demand peaks, reducing the need for expensive and polluting peaking plants.
Adaptation to climate change. Investments in the resilience of power systems
This summer has revealed that conventional power, which for decades was synonymous with reliability, is losing its position in the face of climate change, because thermal power plants, especially those with open cooling systems, are becoming vulnerable to droughts and heatwaves, which forces power system operators to make massive capital expenditures on adaptation measures. The French operator RTE announces the allocation of 24 billion euros by 2040 to modernise the network, so that 80 percent of the infrastructure is made resilient to climate change through a combination of physical reinforcement, digitalisation and new operational procedures. Germany, thanks to its high share of solar PV and energy storage, copes with summer demand peaks better than many other countries, because its system has been designed with flexibility in mind and can adapt to changing conditions more quickly than those relying on large, inflexible baseload plants.
For Poland, the experiences of this summer are a clear warning signal, because the rise in energy prices and call-ups on the capacity market show that the system is vulnerable to extreme weather events, and without action, these vulnerabilities are likely to worsen as the climate continues to change. To ensure supply stability in the future, investments in energy storage, grid modernisation and the development of flexible generation sources are necessary, because only a diversified and flexible system can cope with the challenges of a warming world. One heatwave has not yet changed the mindset of all decision-makers, but it provides a good foundation for a broader debate on the future of European energy, because if we can already feel how difficult it is to balance the system in the face of extreme weather events, it is worth thinking about long-term strategies that will take climate change into account when planning the construction of further generation sources and modernising existing infrastructure.
This is no longer a matter for the future, it is a challenge of the present that requires immediate action on an unprecedented scale, because every year of delay makes the necessary adaptation more costly and the risk of major supply disruptions greater.
Photo: Pixabay
