Data Centres in Slough: Capacity, Operators and Power Constraints
How big the Slough cluster is, who is there, why power is the constraint, and what a rooftop array can realistically do.
Slough's live data centre capacity grew from 115 MW in 2017 to 416 MW in 2025, according to DC Byte figures that SEGRO sent to Slough Borough Council on 13 October 2025. The same source puts the wider "London" market, which it draws across most of southern England and part of south Wales, at 1,478 MW live. Power, not land, is now the limit: the Greater London Authority's consultants report connection timelines of 7 to 13 years in West London.
How big is the Slough data centre cluster?
Slough's cluster sits along the M4 west of Heathrow and is usually described as the UK's densest. There is no official register of data centres, so the numbers below come from one commercial tracker (DC Byte), supplied to the council by a landowner and developer with an interest in the market. They are useful for direction and scale, not as an audited count.
| Year | Total live supply (MW) | New live supply that year (MW) |
|---|---|---|
| 2017 | 115 | n/a |
| 2018 | 132 | 17 |
| 2019 | 162 | 30 |
| 2020 | 177 | 15 |
| 2021 | 221 | 44 |
| 2022 | 290 | 68 |
| 2023 | 299 | 9 |
| 2024 | 369 | 70 |
| 2025 (to October) | 416 | 47 |
Source: DC Byte figures for the "Slough AZ" (availability zone), emailed by SEGRO to Slough Borough Council on 13 October 2025 and published in the council's examination documents (council file ID05). Capacity is the live supply in megawatts of IT power; it is not the same as the electricity each site draws.
Capacity added in 2022 (68 MW) and 2024 (70 MW) was the largest in the series, then 2025 slowed to 47 MW by October.
Who operates data centres in Slough?
No complete public list exists. Operators that have publicly reported Slough capacity or sites include Equinix, Rackspace and Iron Mountain (named in Financial Times reporting on West London power), Digital Realty (which bought a Slough campus), Kao Data (a 16 MW Slough facility), Microsoft, and VIRTUS. Treat the list as a starting point: operators merge, rebrand and sell campuses, and several buildings are colocation halls shared by many tenants.
SEGRO, which owns the Slough Trading Estate, supplied the capacity figures above to the council, so the numbers reflect a landowner's view of the market.
The West London grid constraint
Slough is outside Greater London, but it shares the West London power problem. In December 2025 Buro Happold published an evidence report for the Greater London Authority. It found that transmission grid limits have emerged particularly in West London, and that new connection timelines for data centres may run 7 to 13 years, against 3 to 7 years in other European markets. It also noted a surge in demand connection applications that prompted Ofgem to move connections reform from "first come, first served" to "first ready and needed, first connected" (GLA / Buro Happold, London's Data Centre Future Growth Forecasts and Strategic Insights, December 2025).
The distribution network operator for the Slough area is SSEN; the report names SSEN substations and National Grid transmission infrastructure as the assets serving the Park Royal, A40 and Heathrow corridor next door. For a new load, the practical meaning is that a site with an existing connection is worth more than the land around it. That explains both the growth on existing campuses and the attention on what on-site generation can and cannot do where the queue is long.
Planning: green belt and the 147 MW question
Slough has also been the test case for data centres on green belt. A scheme of 107 MW, expandable to 147 MW, went to a public inquiry opening on 14 October 2025 after the council signalled it would refuse. Data Center Dynamics reported that the Secretary of State approved it on 10 June 2026, concluding the benefits outweighed the harm, with the applicant arguing the part-brownfield land counted as "grey belt" (DCD; confirm against the decision letter on GOV.UK before relying on it).
What Slough's data centres mean for on-site solar
Slough's modelled rooftop yield is 928 kWh per kWp a year for a flat roof tilted 10 degrees facing south, with 14% system losses (PVGIS 5.2 (EU Joint Research Centre), standard calculation, 1 kWp). That is among the highest figures in the UK, in line with the rest of the Thames Valley.
The scale mismatch matters more than the yield. A 1 MWp rooftop array at 928 kWh/kWp generates about 928 MWh a year. A hall that averages 5 MW of IT and cooling load uses about 43,800 MWh a year, so that array covers roughly 2% of it (illustrative arithmetic, not a measurement). Rooftop solar on a data centre is therefore a cost, carbon and resilience measure at the margin, not a way around a grid queue. Because the load is flat, around the clock, almost every kilowatt-hour is self-consumed, which is why the economics are decided by roof area and structure rather than by export prices.
- Grid connection: any generator above the G98 limit of 16 A per phase needs a G99 application to the network operator; a zero-export design simplifies the study. See G99 for data centres.
- Roof and structure: flat membrane roofs over live halls need a ballasted design and an insurer-reviewed method. See data centre solar PV systems.
- Local solar guide: solar panels for data centres in Slough covers the Thames Valley cost and payback assumptions.
Frequently asked questions
How much data centre capacity does Slough have?
DC Byte figures supplied to Slough Borough Council by SEGRO on 13 October 2025 put live supply in the Slough availability zone at 416 MW in 2025, up from 115 MW in 2017. The wider London market is 1,478 MW on the same tracker. There is no official register, so counts differ by source.
Who is the network operator for Slough data centres?
SSEN is the distribution network operator for the Slough area, and National Grid Electricity Transmission owns the transmission network above it. Large new loads usually need both: a distribution connection and, above a certain size, transmission-level studies.
Why is West London's grid constrained?
A December 2025 report for the Greater London Authority found transmission limits in West London and connection timelines of 7 to 13 years for data centres, and a surge in connection applications that led Ofgem to reform the queue to favour projects that are ready and needed.
Can solar panels solve a data centre's power shortage in Slough?
No. At Slough's modelled 928 kWh per kWp, a 1 MWp roof array supplies roughly 2% of a hall averaging 5 MW. It reduces imported electricity and carbon, and the flat load means almost all of it is self-consumed, but it does not replace a grid connection.
Does a rooftop array on a Slough data centre need a G99 application?
Yes, if it exceeds the G98 limit of 16 A per phase, which any commercial array does. The application goes to the network operator before the system is energised, and a zero-export design usually simplifies it.
Pricing solar for a Slough or Thames Valley site?
Four short steps. Your details go to installers who work on critical-power sites; they quote, you compare, no obligation. This site is a publisher, not an installer.