At today’s build rate, Britain runs short of power from 2031.
Demand for electricity is set to almost double by 2040. Britain is building wind, solar and firm power far too slowly to keep up, and plants ordered today will not arrive until the 2030s. This independent model measures the gap and tests two ways of closing it.
Showing NESO’s central pathway, Holistic Transition.
Firm power Britain would be short of under current policy
Extra dispatchable capacity needed to meet the official reliability standard of no more than 3 hours a year without enough power.
Current policy
Wind, solar and batteries built at today’s pace. Gas replaced like-for-like. Nothing else added.
Explore this plan2030–50, incl. grid
Current policy delivered
The same policy built fast enough to work: Clean Power 2030 pace to 2050, plus gas back-up.
Explore this plan2030–50, incl. grid
Nuclear buildout
Small modular reactors from 2039 and one large reactor, with gas and coal back-up while they arrive.
Explore this plan2030–50, incl. grid
Real 2024 pounds, generation, storage, fuel and grid. Current policy looks cheapest only because it does not keep the lights on: the model puts no price on electricity that is not supplied.
Why this matters
- Demand is set to surge. In NESO’s central pathway demand nearly doubles, from about 291 TWh in 2025 to 564 TWh in 2040, as vehicles and heating switch to electricity.
- AI computing comes on top. By mid-2025 about 140 data centres, seeking roughly 50 GW, were queuing for grid connections. Our highest case plans for about 101 TWh a year by 2035 (why we chose that figure).
- Meeting that demand matters for growth. AI is set to be critical to economic growth. Services make up about 79% of the UK economy, and for a services economy like Britain’s, being able to power AI computing at home will be key to staying competitive.
- Wind and solar need firm back-up. In cold, still weeks renewable output stays low for days. NESO has issued seven capacity margin warnings this year.
- Lead times are long. Gas turbine order books are full four to five years ahead and a new combined-cycle station takes five to seven years. Plants needed in the mid-2030s have to be ordered now.
If nothing changes
Counting the projects now under construction, Britain is building about 2.2 GW of offshore wind, 0.55 GW of onshore wind and 1.9 GW of solar a year. That is roughly a quarter to two-fifths of the pace Clean Power 2030 needs. This plan carries that pace forward, with Sizewell C, the Wylfa reactors and the storage and interconnectors already in the pipeline, and replaces retiring gas stations like-for-like. Nothing else is added.
| GW added a year | 2021–25 average | Pace now, with projects under construction | Clean Power 2030 needs | Times faster |
|---|---|---|---|---|
| Offshore wind | 1.25 | 2.2 | 6.5 | 3.0× |
| Onshore wind | 0.47 | 0.55 | 2.3 | 4.2× |
| Solar | 1.63 | 1.9 | 4.8 | 2.5× |
| Batteries | about 1.5 | 2 | 3.6 | 1.8× |
Year-by-year additions and sources
| GW added a year | 2021 | 2022 | 2023 | 2024 | 2025 | Average 2021–25 | Under construction now | Pace used in current policy | Clean Power 2030 pace | Shortfall |
|---|---|---|---|---|---|---|---|---|---|---|
| Offshore wind | 0.87 | 2.59 | 0.89 | 1.41 | 0.51 | 1.25 | 11.85 GW | 2.2 | 6.5 | 3.0× |
| Onshore wind | 0.42 | 0.35 | 0.69 | 0.67 | 0.23 | 0.47 | 2.04 GW | 0.55 | 2.3 | 4.2× |
| Solar | 0.48 | 0.56 | 2.76 | 1.86 | 2.49 | 1.63 | 3.2 GW | 1.9 | 4.8 | 2.5× |
| Batteries | about 1.5 a year (6.8 GW operating at end-2025) | 1.5 | 9.9 GW | 2 | 3.6 | 1.8× | ||||
Not enough power. Under central demand, Britain is about GW short of firm power in 2035, GW in 2040 and GW in 2050. Expected shortfalls reach hours a year by 2050, against a standard of 3.
If the build problem is solved but policy stays the same
This is the best case for the current approach. Wind, solar and batteries are built at the Clean Power 2030 pace every year to 2050, gas is replaced like-for-like, and gas engines and open-cycle turbines are added, as fast as they can be delivered, to meet the 3-hour standard. Beyond Sizewell C and Wylfa, no new nuclear, carbon capture or hydrogen is assumed, because almost none is being built.
Gigawatts a year, built now and needed (average 2031–50)
That has to be sustained for twenty years, plus about GW of new gas engines and open-cycle turbines by 2050. The cost is scale. Wind and solar cannot cover long, cold, still spells and four-hour batteries cannot bridge them, so the system still needs gas back-up for those weeks, while much of the extra wind and solar arrives when there is already a surplus: about TWh is switched off in 2050.
Total cost over 2030–50, including grid connections and network upgrades: £bn.
What about carbon capture?
If the new combined-cycle stations were also fitted with carbon capture, their output would count as clean and this plan would reach about 98% by 2050, at an approximate additional cost of £100bn. It is too early to know that cost with enough precision to model: Britain’s first gas station with carbon capture, Net Zero Teesside Power (742 MW, about £4bn), is not due to start until 2028, and transport, storage and support costs have not been published. The figure scales Teesside’s cost per gigawatt to the plan’s 23 GW of new combined-cycle stations, so it is an indication, not a modelled result.
A different plan
The nuclear buildout keeps the renewables already built or contracted but adds no more. Instead it builds a fleet of small modular reactors from 2039 and one large reactor in 2037, rising to about GW of nuclear by 2050, with gas engines, open-cycle turbines and four coal stations as back-up while the reactors arrive. It is sized to the same 3-hour standard.
Total cost over 2030–50, including grid: £bn, about £bn less than delivering current policy, because reactors on existing sites need far less new grid and run whatever the weather.
The three plans side by side
Total cost 2030–50
| Current policy | Current policy delivered | Nuclear buildout |
|---|
How much AI demand are we planning for?
The AI expansion demand case plans for about 101 TWh a year of data-centre demand by 2035: the 41 TWh in NESO’s higher pathway plus 60 TWh more, or about 11.5 GW running day and night. It is built on that higher pathway, with its vehicle and heating mandates, so it shows the most demand Britain should plan for. It is a planning choice, not a forecast, and it is above every NESO estimate. The other three pathways are NESO’s own, so the finding that current plans fall short does not depend on it.
The evidence, the estimates and why we plan for about 101 TWh
The evidence
- The government’s own forecast. The UK Compute Roadmap (July 2025) forecasts that Britain “will need at least 6GW of AI-capable data centre capacity by 2030”, three times today’s data-centre capacity. Run at 75–95% of capacity, 6 GW is roughly 40–50 TWh a year, around double NESO’s central 2030 figure for all data centres (23 TWh), and it is for 2030, not 2035. The roadmap does not say whether 6 GW is computing load or whole-site capacity including cooling, so the TWh figure is approximate.
- Independent evidence to Parliament. LSE’s Centre for Economic Transition Expertise used a stylised 10 GW at 90% use, which is 79 TWh a year, with a 20 GW high case. Our 101 TWh sits between the two.
- The connection queue. By mid-2025 about 140 data centres were seeking roughly 50 GW of grid connections. NESO judges that close to half of pipeline capacity may be highly speculative or duplicative, but even a modest share would be very large.
- US forecasters keep revising up. BloombergNEF expects US data-centre demand to reach 106 GW by 2035, up from about 25 GW operating in 2024. That forecast is 36% higher than its own estimate eight months earlier. NERC, the North American grid reliability body, now expects peak demand to rise by over 224 GW in ten years, 69% more than it projected a year before, with data centres accounting for most of the increase. US national load forecasts have now been revised up for three years running.
- NESO’s latest view is lower. Its September 2026 Ten Year Outlook cut data-centre demand to about 15 TWh in 2031 and 24 TWh in 2036 (about 22 TWh in 2035), citing updated utilisation data and project attrition. That is well below its own 2025 scenarios and far below the government’s 6 GW forecast. The two official views now differ by a factor of two to three, which is why we plan for the higher end rather than the lower.
| Estimate | Data-centre demand | Year |
|---|---|---|
| NESO Ten Year Outlook 2026 (latest, revised down) | about 22 TWh | 2035 |
| NESO 2025 ten-year forecast (before the cut) | 33 TWh | 2035 |
| NESO 2025 scenarios, lower (Falling Behind) | 20 TWh | 2035 |
| NESO 2025 scenarios, central (Holistic Transition) | 37 TWh | 2035 |
| NESO 2025 scenarios, higher (Electric Engagement) | 41 TWh | 2035 |
| Government 6 GW forecast, at 75–95% use | 40–50 TWh | 2030 |
| LSE stylised case, 10 GW at 90% | 79 TWh | — |
| Our AI expansion case | 101 TWh | 2035 |
| LSE high case, 20 GW at 90% | about 158 TWh | — |
Why we plan for about 101 TWh
- The government’s forecast already exceeds every NESO figure, and it is a 2030 minimum. It implies tripling capacity in five years. If growth continues after 2030, demand in 2035 will be higher still.
- Forecasters have repeatedly underestimated this demand. In the US, the main forecasts have been revised up year after year as data-centre orders arrived faster than expected. NESO has moved the other way, cutting its figure for 2035 from 33 TWh to about 22 TWh. We would rather plan for the upward trend seen in the largest market than assume Britain will be the exception.
- It sits inside the independent range: just above LSE’s 10 GW case and well below its 20 GW high case.
- Government policy is trying to attract computing investment, including faster grid connections for data centres. The supply plan has to be sized for that policy succeeding.
- The risks are not symmetric. Firm power takes five to seven years or more to deliver. Planning too low means investment goes elsewhere and the grid runs short. Planning too high means some capacity is built early. Large loads that bring their own firm power reduce the public requirement one for one, so if demand arrives with its own power, the public plan shrinks.
Checked against NESO
Run on the 2030 system in NESO’s Clean Power 2030 advice, with NESO’s capacities and assumptions, the model reproduces NESO’s results.
| 2030 | NESO | This model |
|---|---|---|
| Renewables share of generation | 77–82% | 78% |
| Gas power stations | 14–15 TWh | 16 TWh |
| Clean share | 95% | 95% |
| Reliability standard (3 hours) | Met | Met (0.3 h) |
Method and evidence
The model is built on over 1,000 documented assumptions from about 100 cited sources and a record of nearly 3,000 existing power stations. For every year from 2030 to 2050 it replays each hour across seven historical weather years and two severe cold spells, with and without trade with Europe, and tests each plan against the official 3-hour reliability standard with random power station breakdowns. Grid connections and wider network upgrades are costed alongside generation, storage and fuel.
All three plans include the interconnectors already approved (rising to about 14.5 GW by 2033), Ofgem’s 16 provisionally selected long-duration storage projects (7.6 GW) and the current limit on moving power from Scotland to England. They narrow the gap but do not close it.
In the explorer the three plans are fully calculated for all four demand pathways. You can edit a plan’s build orders and see capacity and construction spending change straight away. Hour-by-hour results for an edited plan need the full model, which runs on your own computer.