2023-07-02 05:16:39
The Port-Saint-Louis-du-Rhône wind farm / Image: Jean Weber – Flickr CC, editing: RE.
Alone, a wind turbine produces less than a nuclear reactor, that’s obvious. But how many would be needed to replace or at least produce as much as a nuclear reactor? The question is worth dwelling on for a moment.
How many wind turbines are needed to replace a nuclear reactor? Over the course of press articles or posts on social networks, different figures are put forward. Several thousand for some. Barely a few hundred for the others. With results, you imagine, sometimes marred by a certain bias. So, let’s try to see it more clearly.
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It’s not just regarding power
We can, in a first approach, ask the question of power. In France, most nuclear reactors have a power of 900 MW. Some go up to 1,300 MW and others even up to 1,450 MW. Most of the wind turbines installed to date – mainly onshore wind turbines – display a power ranging from 1 to 3 MW “only”. At least 900 MW on one side and at most 3 MW on the other. The calculation is quickly done. It takes a minimum of 300 wind turbines to reach the power of a nuclear reactor. Less, however, if we choose to compare to offshore wind turbines. Their power is already up to 6 MW and might increase further – it is regarding 18 MW. Which brings us to at least 150 wind turbines — at sea — for a nuclear reactor.
But things are not so simple. Firstly, because a wind turbine only delivers its maximum power within a well-defined wind range, between 30 and 90 km/h. If there is no wind or if the wind speed is too low—or even if its direction does not coincide with that of the wind turbine—the wind turbine does not produce electricity. Or it produces them in limited quantities. Ditto when the wind is too strong. It is then necessary to limit the speed of rotation of the blades to avoid damage to the structure.
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Thus, if in fact, wind turbines turn more than 6,000 hours per year, they only produce, according to experts, between 1,500 and 3,500 hours at maximum power. An average of 2,000 hours in Europe out of the 8,760 hours in a year.
Nuclear reactors, too, do not produce every day of the year at full power. They are sometimes stopped to carry out maintenance operations in particular. “EDF defines what is called the availability factor”explains Dominique Vignon, president of the energy division of the Académie des technologies. “It gives an indication of the number of hours in the year during which a reactor is available. » Technically speaking, then. But another factor comes into play. The one that experts call the load factor. “In France, it is regarding 3 points lower than the availability factor. This reflects the fact that sometimes operators intentionally do not operate a reactor at full power. Because consumption needs are not there, or because wind power, for example, produces a lot. »
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The Importance of Load Factor
The concept of load factor is also valid for wind turbines. It corresponds, in general, to the ratio between the electricity actually produced during the year and the electricity which would have been produced if the installation had operated at full power 24/24 and 7/7.
The 2022 electricity report published by RTE thus gives a load factor for French wind power of 21.6%. The lowest in the last 10 years. In question, unfavorable weather conditions. In 2020, this load factor had reached a record on the other side of the scale of 26.6%. According to figures from the same RTE report, the nuclear load factor was 51.7% in 2022. A figure, once more, historically low. The calculations made for this year, which was ultimately unfavorable to the two means of production, show that a 900 MW reactor was able to produce approximately 4.1 TWh of electricity. To produce so much with wind turbines, it would have been necessary to count on an installed capacity of 2,170 MW, i.e. still considering wind turbines of 3 MW each, out of more than 720 wind turbines.
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But can this calculation for the year 2022 be generalized? “In fact, the load factor of onshore wind power in France has been fairly stable for ten years”, comments for us Dominique Vignon. About 23%. “Because even if it is true that the potential for capturing the wind by the most recent wind turbines has increased, the sites on which they are now located are no longer the best. There is probably a compensating effect between these two phenomena. For nuclear, it’s different. We had load factors that reached 80% over several periods. But due to the large fairing and stress corrosion issues, they went down a lot. I see no reason why they should not rise to 80% over the next ten years or so. Especially since it is not particularly high compared to what we see abroad. » In the United States, for example, the nuclear load factor is around 90%. The reactors there are however piloted differently from the French reactors.
What impact of climate change on production?
The question that may arise is whether these load factors will be affected by climate change. With regard to wind power, first of all, “Experts estimate that it might drop by one point by 2050”, explains the president of the Energy Pole of the Academy of Technologies. The reason: expected less powerful winds on the one hand and more frequent periods of storms on the other. Both situations being unfavorable to wind power generation. And as far as nuclear power is concerned, seaside power stations should not experience any variation in their load factor.
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Those on the banks of rivers will no doubt have to deal with longer periods during which they will have to operate at partial load. To avoid disturbing ecosystems by discharging water that is too hot. “But the effect will be small because in summer a number of reactors are shut down for maintenance anyway”, points out Dominique Vignon. So there too, the loss of production will remain minimal. “In the end, there will be an impact on both wind and nuclear, but it will not change the situation. »
What changes it, to a certain extent, is the arrival of offshore wind power. Today, there are still very few of them in France. But projects are launched. “And the load factor of offshore wind is significantly better than that of onshore wind. » Around 40%. Thus, to produce as much electricity as a 900 MW nuclear reactor, it would be necessary to install 1,170 MW of offshore wind power.. That is, for offshore wind turbines with a unit power of around 6 MW, something like 195 offshore wind turbines. “By adding offshore wind power, the overall average load factor for French wind power will therefore increase. »
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Beyond numbers, a system problem
But what these calculations do not yet take into account is the lifespan of wind turbines compared to that of nuclear reactors. From single to double. At the minimum. Since we give between 15 and 25 years for an onshore wind turbine, between 20 and 30 years for an offshore wind turbine and at least 50 years for a nuclear reactor. What, suddenly, double the number of wind turbines needed to produce as much as a nuclear reactor.
And even with that, these raw numbers are still not enough to draw a fair comparison. “Because it all has to fit into a system. Wind power produces according to the weather. Its deployment is necessarily accompanied by network costs and system costs linked to the need in particular to add storage capacities. Not to mention the issue of the environmental footprint. That of land use and material consumption”concludes Dominique Vignon.
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