You may have read it: in France, data centre projects are calling for 18 gigawatts of electricity. One gigawatt is roughly the output of a large nuclear reactor. Eighteen of them, and you can picture a grid on the verge of collapse.
The figure is accurate. But it does not mean at all what people think it means.
What the figures actually say
According to RTE, the French electricity grid operator, data centres today consume around 10 terawatt-hours a year, or close to 2% of the country's electricity. The vast majority are in the Île-de-France region.
What has exploded is the requests. By mid-2026, around 80 projects had booked close to 18 gigawatts of connection capacity, against 5 gigawatts at the end of 2024. Most are asking for between 100 and 200 megawatts, the equivalent of a city such as Le Mans. Around ten are targeting more than 400 megawatts. The largest, an AI campus in Fouju, in Seine-et-Marne, signed a contract in January to go up to 1.4 gigawatts.
The catch: booking is not consuming
Here is the essential point. Booking connection capacity is like reserving a very large pipe just in case. It does not mean you are going to fill it.
RTE has found as much: data centres connected over the past two or three years use on average only 20% of the capacity they had requested. Many projects book capacity without ever using it, or take ten to fifteen years to reach full operation. RTE calls them "phantom projects", which clog up the queue at the expense of solid ones.
As a result, official forecasts are far more modest than the 18 gigawatts: between 15 and 20 terawatt-hours in 2030, or around 3% of French electricity, then 23 to 28 terawatt-hours in 2035, around 4%.
The whole confusion comes from two units that look alike. The gigawatt measures power, like the diameter of a pipe. The gigawatt-hour, or the terawatt-hour, measures a quantity of energy, like the water that has actually flowed. A 1-megawatt device running all year consumes 8.76 gigawatt-hours. And the 10 terawatt-hours consumed each year by all French data centres correspond to an average power of barely more than one gigawatt. So we are a long way from the 18 gigawatts booked.
The real questions
That is not to say everything is fine. French electricity is more than 95% decarbonised, which is a real asset, and RTE considers production sufficient. But data centres raise other questions.
Land. The large campuses occupy dozens of hectares, often farmland.
Water, used to cool the machines in some facilities.
Consultation. A decree published in March 2026 removed some of these projects from consultation with the Commission nationale du débat public, and a bill was considering making them projects of major national interest, which worries environmental associations.
In the United States, a Virginia county with 250 data centres shows what happens when local residents' concerns are forgotten: tax revenue, and growing anger.
What to take away
The 18 gigawatts are not an imminent threat to the grid. They are bookings, a good share of which will never materialise.
The right question is therefore not "how many gigawatts?", but "which projects will actually be built, where, and with what trade-offs for the areas that host them?". That is where the acceptance of data centres in France will be decided.