What hot weather shows us about the relationship between solar energy, nuclear power, climate and ecology.
Prolonged hot weather affects the entire European energy system. Solar panels generate plenty of electricity, while some nuclear power plants are able to produce less. These plants use river water for cooling. If that water becomes too warm, they have to reduce their output to prevent damage to ecosystems.
This combination shows just how closely energy, climate and ecology are connected. And why a robust energy system is about more than generating as much energy as possible. It is also about making smart use of the renewable energy available when the system needs it most.
Warm river water limits electricity production
Many nuclear power plants use water from rivers to cool their installations. After use, that water flows back into the river at a higher temperature. Strict limits apply to this. They prevent river water from becoming too warm and damaging ecosystems.
During prolonged hot weather and periods of low rainfall, river temperatures rise. Nuclear power plants may then have to reduce their output or temporarily shut down because the river water is too warm to be used for cooling within ecological limits. This happened at several nuclear power plants in France this summer.¹
At the same time, hot weather often increases electricity demand, for example due to greater use of air conditioning. This was also the case in France this summer.² As a result, less electricity may be available from nuclear power at the same time as demand is increasing.
This is not a choice between energy production and ecology. The limits are there for a reason. They make it clear that energy generation does not exist separately from its surroundings. Water, temperature, nature and electricity production all influence one another.
More room for solar energy
When part of the usual electricity production falls away while demand remains stable or rises, the balance in the energy market changes. This creates more room for other energy sources, including solar energy.
That change does not stop at national borders. European electricity markets are interconnected. Electricity is traded between countries, provided there is enough capacity in the interconnections and electricity grid. Lower nuclear power production in France can therefore also affect demand, supply and prices in neighbouring countries.
For solar parks, this can mean that they need to curtail their output less often during sunny periods.
Why do solar parks sometimes curtail their output?
During sunny periods, more electricity can be generated than the market or electricity grid can handle. Solar parks then temporarily reduce their output. This is known as curtailment.
Sometimes this happens because supply is greater than demand. In other cases, the local electricity grid does not have enough capacity to transport the electricity being generated.
Hot weather mainly affects the first situation. Because other energy sources produce less and electricity demand increases, more room becomes available for solar energy. Solar parks then need to curtail their output less often because of an oversupply in the market.
This does not make local grid congestion disappear. An oversupply in the electricity market and a congested electricity grid are two different bottlenecks. Higher demand can mean that more solar energy is needed, but it does not increase the capacity of a full cable. There still needs to be enough capacity on the grid to actually transport that electricity.
Putting more green energy to use
Less curtailment means that we actually use more of the solar energy available. Electricity that would otherwise not have been generated can now make its way to households, businesses and other consumers.
That is exactly what the energy transition is about. Not only generating more renewable energy, but also making sure we use that energy when it is available.
Electricity consumers also play an important role in this. Businesses that plan their consumption intelligently can use more green electricity at times when supply is high. For example, by charging electric vehicles, operating installations or storing energy for later use.
By connecting generation, storage, smart consumption and energy management, we get more out of every sustainably generated kilowatt-hour.
The right energy at the right time
Extreme heat puts pressure on both nature and the energy system. At the same time, this situation makes clear what the energy transition is really about.
Not only generating more renewable energy. Also making sure that energy reaches the right place at the right time.
That is why Novar is building energy systems in which generation, storage, smart energy management and energy consumption come together. This allows us to make better use of renewable energy at the moments when it is both available and needed.
Less curtailment. More green energy put to use. That is how we get more out of every sustainably generated kilowatt-hour.
Sources
¹ Reuters, Europe’s heatwave curbs French nuclear plants, 24 June 2026.
² RTE, Canicule : la sécurité d’approvisionnement en électricité n’appelle aucune vigilance particulière, 22 June 2026, updated 25 June 2026; RTE, Bilan du système électrique – Premier semestre 2026, 16 July 2026, p. 13.
