Danube temperature and Paks power output explained

The Danube’s summer warming is not only an environmental issue, but also a very tangible financial factor in Hungary’s electricity system. According to calculations by REKK researchers Balázs Felsmann and András Mezősi at the Regional Centre for Energy Policy Research, the capacity restriction at Paks between 18 July and 26 August 2026 may have caused HUF 37.4 billion in additional trading costs. It is important to note, however, that this is not an official MVM final figure, but an independent model calculation, and the research’s original source document is not included in the editorial package.

The logic of the estimate is simple: when Paks produces less electricity because of cooling constraints, the missing volume has to be replaced from elsewhere. If this can only be bought on the market at a higher price, the difference appears as an additional cost. According to the current analyses, this is exactly what happened during the forced summer output reduction.

What does the Danube have to do with the nuclear plant’s output?

The Paks Nuclear Power Plant uses water from the Danube for cooling, so the state of the river directly affects operations. If the water temperature is high and the water level is low, cooling options deteriorate and the output of the units has to be reduced.

According to the editorial package, in the summer of 2026 the problems of a warming Danube and low water levels occurred at the same time. Reports on the issue said the Danube’s water level at Paks fell to minus 118 centimetres on 29 July, showing how extreme the situation had become. These data appeared in several press sources, but no primary regulatory or operator document is available in the package, so the details should be treated with caution.

How large was the shortfall?

According to the available summaries, the output reduction period lasted from 18 July to 26 August. Based on figures cited by Infostart, the volume of lost electricity generation was 922 GWh, that is 922,000 megawatt-hours. On its own, this is already a large enough item to be felt on the procurement side of Hungary’s electricity system.

According to the calculation used for the REKK model, the production cost of Paks electricity was taken as HUF 14.02 per kilowatt-hour, based on the 2025 financial report. The additional trading cost is therefore not the full market purchase price itself, but the difference between the market replacement price and Paks’s production cost. This is an important clarification, because the HUF 37.4 billion does not refer to general “damage”, but to a replacement premium calculated using a specific methodology.

How was the HUF 37.4 billion figure reached?

Based on the available reports, REKK researchers Balázs Felsmann and András Mezősi compared the lost Paks generation with the cost of market replacement. If the electricity that was not generated had to be bought at high spot or import market prices, while Paks could have produced it at a much lower cost, then the difference between the two gives the additional bill.

According to reports by Telex and Infostart, this model produced a figure of HUF 37.4 billion. On peak days, the daily additional replacement cost may even have exceeded HUF 2 billion, according to figures published in the press. This clearly shows why a prolonged summer restriction can become a tens-of-billions item within a few weeks.

Why may the actual loss not have been exactly this much?

One of the most important uncertainties in the editorial package is precisely that there is no available MVM statement on the actual, recognised financial result. For that reason, the HUF 37.4 billion cannot be treated in the article as a final, official figure. It is more accurate to say that this is an independent model calculation by REKK researchers of the additional trading cost.

According to an analysis by Reakció, the figure may be a conservative upper estimate. The reason is that the calculation may have been based on spot market prices, while in reality MVM may have had forward or bespoke electricity procurement contracts that reduced the actual replacement cost. Since there are no public, verifiable data in the package on those contracts, no more precise claim can be made.

What does this show about the Hungarian energy market?

The story goes beyond one power plant in one summer. Paks generation plays a key role in domestic electricity supply, so if a lasting restriction occurs there, the system tries to balance it elsewhere, typically through imports or more expensive market purchases. In the end, this appears in energy market costs and, indirectly, in the burden on the entire supply system.

The current situation also shows that climate change is not an abstract future risk in the energy sector. Heatwaves, low water levels and warmer river water can already limit power plants that are built around stable baseload generation. The more frequent such summers become, the greater the cost of adaptation will be.

Could the loss have been avoided?

The editorial package also includes a claim that certain technical upgrades or water management investments would have been cheaper than the losses caused by the summer shutdown. However, this is only a medium-confidence claim based on secondary sources, and there is no primary technical or investment documentation behind it. For that reason, it cannot be written up as a firm conclusion.

A more cautious way to put it is that, based on the scale of the currently estimated additional cost, the importance of any development that could reduce the risk of lost generation arising from cooling constraints is increasing. Which specific investment would have been technically, legally and economically justified could only be judged responsibly on the basis of primary professional and regulatory documents.

Why is it important to clarify the methodology?

In cases like this, it is easy to confuse three different things: the amount of electricity that was not generated, the cost of market replacement and the actual loss shown at company level in the accounts. According to the available information, the HUF 37.4 billion cited here belongs to the second category: a modelled additional trading cost.

This matters because, in public debate, a large number can very quickly turn into a “final loss”. But given the current source situation, all that can be said with greater confidence is that, according to the model, the summer restriction at Paks may have caused a significant additional replacement cost in the tens of billions of forints. To arrive at a precise final figure, a primary REKK document, MVM data and ideally background material from MAVIR or the relevant authorities would also be needed.

What does this mean for readers?

The main lesson is that the cost of energy security is becoming increasingly linked to weather and water management risks. If environmental conditions limit the output of a large power plant, the effect does not stay within the plant’s fence line: it appears in wholesale electricity prices, import demand and, ultimately, in the financial balance of the entire system.

For that reason, this case is not only a summer technical episode, but also a warning. The Danube’s temperature and water level may continue to determine how steadily and at what cost Paks can generate electricity, and with it how much it costs Hungary to maintain supply during hot, drought-stricken periods.