If the four projects ran continuously at full capacity, BBC calculations showed they would need 1.3 gigawatts and could produce an estimated 4.1 million tonnes of carbon emissions a year. One scheme would have a power load of 1 gigawatt, equivalent to 200,000 to 250,000 average UK homes.
Developers face waits of up to 10 years for National Grid upgrades. Some have been told they may wait that long for a connection to an already strained system.
Data centres — warehouses of servers for streaming, banking and public services — have been part of the British landscape for more than two decades. A new generation due in coming years will be far larger to serve more sophisticated AI.
They will consume considerably more energy than earlier sites while the grid struggles to meet demand.
A critic said that if gas plants were allowed, it would set a precedent for gas-fired stations across the country and make environmental and net-zero targets extremely difficult to hit. He said 1 gigawatt of solar would need an area equal to 15 per cent of Bedfordshire, and that wind power was intermittent and expensive.
In Cardiff, a developer is seeking permission for a temporary energy centre with turbines of up to 49.9 megawatts. Planning documents said it could run for up to five years if a grid link is not secured quickly. At Acre Slough, west of London, developers said they could use gas engines of up to 49.5 megawatts while waiting for a grid connection they expect could take at least 10 years.
Ofgem said data-centre developers are seeking connections totalling 72 gigawatts. Peak electricity demand across the country last year was 45 gigawatts. All four projects said they intend to connect to the national grid when it can meet their needs, reducing reliance on fossil fuels.