What questions should you ask about a data centre project?

In May 2026, about 80 data centre projects had reserved nearly 18 GW of grid connection with RTE. For an elected official, an association or a resident, each project arrives with a thick technical file, and a public meeting where questions are often asked in no particular order. Our analysis of contested projects has read 3 of these files; this guide draws from them a list of questions, topic by topic.

For each question, we give the answer a project developer should be able to give, and a published reference value to judge it by. These values are averages or regulatory thresholds: they serve to place an answer in context.

The connection power is the figure put forward, and it says little about consumption. A centre almost never draws all of it: in 2025, data centres connected to the transmission network used only 22% of it on average, and operators expect to rise towards 80% in 10 to 15 years, according to RTE. Annual consumption says what the centre will consume; for the Microsoft project at Petit-Landau, the environmental authority of Grand Est estimates it at the consumption of more than 280,000 households, about 80% of that of the households of Haut-Rhin.

The connection substation counts as much as the power. A grid becomes saturated locally, as in the Dublin region, well before energy runs short at national scale; our analysis of the electricity shortfall details these quantities. A commitment to demand response at winter peak hours can feature among the questions: a centre that steps aside for a few hours a year frees up power for heating and industry.

Water depends first on the cooling method. Dry cooling, chosen for phase 1 at Fouju, withdraws almost nothing locally; it relies on chillers charged with fluids: 601 tonnes of refrigerant gas at Fouju, according to Next. Evaporative cooling consumes water; the question then becomes that of the basin and its summer stress. Our analysis of the water use of data centres gives benchmarks basin by basin.

Heat is almost all of the electricity consumed, rejected at low temperature. The 2023 European Energy Efficiency Directive requires centres of more than 1 MW to recover it, unless they demonstrate that this is not technically or economically feasible; according to the 2024 declarations, the EU's reporting centres reused 1.8% of it. Our explanation of heat says why: it takes a nearby heat network, and demand in summer.

Backup generators are tested regularly and emit nitrogen oxides. At Meudon, the environmental authority counted 33; at Petit-Landau, it notes a rise of about 20% in the nitrogen oxide emissions of Alsace. In the files submitted, their total thermal power is classified under combustion: declaration with inspection from 1 to 20 MW, registration from 20 to 50 MW, authorisation from 50 MW, a threshold that also makes environmental assessment systematic.

Surface area partly decides the procedure. Combustion of 50 MW or more, a development operation of 10 hectares or more, or a construction of 40,000 m² or more subject the project to environmental assessment, and therefore to a public inquiry; a substation of 63 kV or more, a plot of 5 to 10 hectares or an installation subject to registration go through a case-by-case review. At Aulnay-sous-Bois, the environmental authority took into account the combustion, the 225 kV substation and a plot of 12.1 hectares. The question of soils follows: farmland at Fouju and Petit-Landau, an industrial brownfield for the MRS5 centre in Marseille.

On jobs, no public source gives a ratio of jobs per megawatt: the developer must be asked for its direct operating jobs, distinct from those of the construction phase. A data centre pays the property tax on built properties; the amounts expected for the municipality and the intercommunal body appear in none of the 3 files we read.

On data, every centre of 500 kW of IT load or more reports each year to the European register its energy, its water, its reused heat and the types of refrigerant it uses. The 2024 regulation publishes these declarations only aggregated by country, and keeps those of each site confidential. In its September 2026 report, the Commission announces a delegated regulation creating a label per centre, built on some of these indicators and accessible to the public. The 2023 directive, on the other hand, asks operators to make their information public, subject to commercial secrecy. A developer can therefore commit to publishing each year, for its site, what it declares.

The environmental authority issues a simple opinion; the developer responds in writing, and the prefect decides on the environmental authorisation. The municipality sets the planning rules, RTE connects. A law of 26 May 2026 allows a data centre to be designated by decree as a project of major national interest, which entrusts the planning permit to the prefect. The questions in this list are useful at each of these moments: the prior consultation, the public inquiry, the local deliberation.