Europe is groaning under an extraordinary Heat wave. While millions of people run their air conditioning at full blast, the European electricity system is coming under extreme pressure: nuclear power plants in France are throttling their output, wind power is largely absent, and even solar systems are delivering less than expected. The consequences are historic price spikes on the short-term markets—and a case study in the vulnerability of centralized energy supplies during extreme weather events.
Record prices in the 15-minute markets
On June 23, 2026 intraday electricity prices reached historic highs in several European countries. The volume-weighted 15-minute average price (VWAP) reached the following 15-minute peaks:
| Country / Bidding zone | Quarter-hourly price (peak) | Time window |
| Belgium | 1,038.25 €/MWh | 8:45 PM – 9:00 PM |
| Netherlands | €902.47/MWh | 8:45 PM – 9:00 PM |
| Denmark (DK1) | 786.83 €/MWh | 8:45 PM – 9:00 PM |
| Germany | 747.10 €/MWh | 8:45 PM – 9:00 PM |
| Austria | 712.40 € / MWh | 8:45 PM – 9:00 PM |
| France | 414.20 € / MWh | 9:00 PM – 9:15 PM |
The sharpest price spikes occurred in the evening – precisely when solar power generation drops off after sunset, while temperatures and thus the demand for cooling remain high. In Germany, the residual load – that is, the portion of electricity demand not met by wind and solar energy – rose to 51.5 gigawatts. This corresponds to a Surplus of around 10.4 GW compared to the seasonal norm.
(⚡Residual loadThis is the electricity demand minus the feed-in from wind and solar. The higher the residual load, the more conventional power plants have to step in – and the more expensive electricity becomes.
Many effects: Why extreme heat impacts the power system
The current crisis is not an isolated phenomenon – it is the result of several effects acting simultaneously:
| Factors | Effect in extreme heat |
| Cooling demand | Air conditioning systems massively increase electricity demand – simultaneously and at short notice. |
| Calm | Low-Wind Event: During high-pressure weather conditions, wind power generation in Northwestern Europe often collapses. |
| Thermal power plants | Gas and steam power plants as well as nuclear reactors are operating at reduced output due to insufficient cooling |
| PV efficiency | Silicon solar cells lose approximately 0.4 %/°C in efficiency at high module temperatures. |
| High residual load | In Germany, the residual load rose to 51.5 GW – about 10.4 GW above the normal value for this time of day and year. |
What makes this situation particularly delicate: All Effects act simultaneously and reinforce each other. High demand meets limited supply from almost all sources – a systemic risk that is difficult to buffer with conventional centralized supply.
The Nuclear Problem: When Cooling Fails
Nuclear power plants require large amounts of cooling water. These can be lacking during a heat wave when rivers dry up, so that a complete standstill threatens. But even at low water levels, the water temperature in flowing bodies of water rises to such an extent that discharging the additionally heated cooling water would push the river temperature above regulatory limits. Environmental protection and security of supply come into conflict.
As a result, the French state-owned electricity company EDF has initiated concrete measures:
- The Golfech Nuclear Power Plant on the Garonne was in the night of June 23 shut down.
- For the also located on the Garonne Blayais Power Plant were Limitations announced.
- The same applies to Rhône Power Plants Bugey and Saint-Alban.
EDF emphasizes that, on average since 2000, annual production losses due to heat-related curtailments have amounted to only 0.3 %. However, the company itself acknowledges that if heat events become more frequent and intense, the impacts could increase significantly. Climate scientists confirm this assessment—an analysis by World Weather Attribution shows that the current heat event is likely to have been up to 4 degrees Celsius hotter due to climate change than it would have been in a world without human-induced warming.
France had already during the hot summers 2003, 2006, 2018 and 2019 implement temporary power reductions or shutdowns of its nuclear reactors. In 2022 as well, extreme drought and prolonged heat caused rivers (such as the Rhône and the Garonne) to have historically low water levels that were also very warm. Only through massive electricity purchases from neighboring countries could the power supply be maintained.
Since then, cooling water limits in France have been capped by regulatory requirements. If the discharge temperature exceeds the permitted value, the power plant must throttle output or shut down—regardless of supply demand.
The solar paradox: Lots of sun, less electricity
It seems counterintuitive: with maximum solar radiation, photovoltaics should be running at full speed. In reality, however does the efficiency of silicon solar cells decrease with increasing temperature. The background is the physical relationship between cell temperature and the so-called temperature coefficient:
- Crystalline silicon cells lose approximately 0.35 to 0.45 % of their power output for every degree Celsius increase in temperature above standard test conditions (25 °C).
- At a module temperature of 70 °C—which is quite realistic in practice on a midsummer day—this can result in a loss of efficiency of up to 20 %.
- Montel confirms: Despite intense solar radiation, the efficiency of the PV systems decreased on June 23 due to high module temperatures.
In addition, solar power feed-in drops rapidly in the evening – precisely at the time of peak load. The supply gap between the falling solar supply and constant cooling demand is currently still closed by expensive conventional power plants.
Outlook: The situation remains tense
The Swedish meteorological service SMHI forecasts that the heatwave in Central and Western Europe will continue into the first days of July. As a result, no short-term relief is to be expected in the European electricity markets. Several structural questions arise:
- How frequently and how intensely will such heat events occur in the future?
- How resilient are European electricity grids when all supply sources are under stress simultaneously?
- What role can decentralized, heat-independent solutions play in increasing system resilience?
The current situation impressively shows that an energy system that relies on several unreliable sources simultaneously in stress situations urgently needs complementary flexibility solutions – on both the supply and demand sides.
Battery storage in the heatwave: Opportunities and limits
Battery storage (BESS) respond on demand – regardless of wind, water levels, or cloud cover. This makes them one of the few truly flexible instruments in the power system during supply crises such as the current heatwave. Nevertheless, it would be incomplete to portray BESS as entirely independent of heat.
Cooling as a system requirement
Lithium iron phosphate (LFP) cells, which are standard in large-scale stationary energy storage systems today, operate optimally at temperatures around 20 to 25 °C. Container BESS are therefore equipped with active climate control as standard. During prolonged extreme heat, the internal consumption of these cooling systems increases—and with it, the net system efficiency drops. Furthermore, battery management systems (BMS) activate protective functions when cell temperatures are too high, which can limit charging and discharging performance. In short: BESS do not need river water, but they do need cooling – and this must be designed for extreme weather scenarios during system planning.
Arbitrage: The Strongest Argument
Nevertheless, grid-connected FTM battery storage systems are worth their money in situations like June 23, 2026. A large-scale storage system that charges in the morning when prices are low and discharges in the evening during the peak load phase achieves spreads during price spikes of 747 to over 1,000 EUR/MWh that all operating costs including cooling energy exceed by multiple times. Business models are designed precisely for situations like this. Day-Ahead Trading and Intraday Trading with BESSS.
Balancing energy and grid stability
FTM-BESS also provide system-critical services: primary control reserve (PCR) and secondary control reserve (SCR) can be provided by battery energy storage systems within seconds – a capability that thermal power plants do not possess at this reaction speed. In stress situations, in which several large power plants throttle down simultaneously, this capability for frequency stabilization through the provision of Control energy not not only economically valuable, but also systemic.
FAQ: Frequently asked questions about the heatwave and the electricity market
Why does solar power produce less electricity in extreme heat?
Crystalline silicon solar cells lose efficiency as the operating temperature rises. Depending on the module type, the so-called temperature coefficient ranges from approximately −0.35 to −0.45 % per degree Celsius. At module temperatures of 65–75 °C on hot summer days, the actual power output can be significantly below the rated value—even when solar irradiance is at its maximum.
Why do nuclear power plants have to be throttled during hot weather?
Nuclear power plants draw cooling water from rivers. The warmed water is discharged back after the cooling process. Regulations limit the maximum temperature of the discharged water to protect ecosystems. If the river water is already too warm, sufficiently cold cooling water cannot be drawn—the facility must reduce output or shut down.
What is residual load and why is it so high during heatwaves?
The residual load describes the portion of electricity demand that is not covered by renewable energies (in particular wind and solar) and must therefore be provided by conventional power plants. During heat waves, total demand rises sharply due to air conditioning, while wind and (to a certain extent) solar power are limited at the same time. The result is a very high residual load – with corresponding impacts on electricity prices.
What does that mean for companies with their own electricity storage system or PV system?
Companies that have invested in a battery storage system benefit in multiple ways: they can use self-produced or purchased electricity cheaply during expensive peak-load phases themselves (peak shaving) or—depending on the system design—feed it into the grid. PV system operators should take the temperature coefficient of their modules into account during planning and consider the possibility of integrating a battery to shift solar yields into the evening hours.
Sources
- Montel / pv magazine Germany: „Heat wave drives European electricity prices to record levels“, June 23, 2026
- Keystone-SDA / Nau.ch: „Nuclear power plant in France throttled due to heatwave“, June 23, 2026
- SMHI (Swedish Meteorological and Hydrological Institute): Heatwave forecast Central and Western Europe, June 2026
- World Weather Attribution: Climate change analysis of the 2026 Western Europe heatwave