The UK Energy Problem

An interactive model of Britain’s electricity system measuring how far current plans fall short and tests how to close the gap.

Model version 2.5 · updated 23 October 2026

Why we built this

Electricity demand is set to almost double by 2040, but current plans don’t provide enough power for cold, still winter days, and the plants needed take years to build, so Britain risks running short from the early 2030s. We built the model to test options for solving that problem, and to understand how big and how urgent it is.

Demand is set to surge. In NESO's central Holistic Transition pathway, demand nearly doubles, from about 291 TWh in 2025 to 564 TWh in 2040. In that pathway, which is built to meet today's net-zero targets including the vehicle and heating mandates, electric vehicles rise from 9 to 111 TWh and heat pumps and heat networks from about 1 to 44 TWh.
AI computing comes on top of that. By mid-2025 about 140 data centres, seeking roughly 50 GW, were queuing for grid connections. The government's own forecast that Britain will need at least 6 GW of AI-capable capacity by 2030 implies roughly 40–50 TWh a year, already above NESO's central 37 TWh for all data centres in 2035. Our programme case plans for about 97 TWh by 2035 (why we chose that figure).
Wind and solar need firm back-up. On cold, still winter days, renewable output can stay low for long periods. The grid then depends on dispatchable plant and imports: Britain has imported about a tenth of its electricity in recent years, and NESO issued six capacity-margin warnings this summer.
Lead times are long. Large gas turbines come mainly from three manufacturers, whose order books are full four to five years ahead. A turbine ordered today would not arrive until about 2031, and a new combined-cycle station takes five to seven years from order to power. New nuclear takes longer still and planning and grid-connection rules cause further delays. Plants needed in the mid-2030s have to be ordered TODAY.
Missing it has a cost. Without enough firm power, Britain risks losing AI and industrial investment to countries that can connect it, slower growth, greater dependence on imports, and a less stable grid.

The model's own results underline the urgency. Current plans miss the 3-hour reliability standard from 2031 under every NESO demand pathway (see below). Even if a government elected in 2029 embarked on a massive scaleup of energy generation, the buildout could not meet the standard in 2031–34 because no new plant can be built in time.

Figures: NESO Future Energy Scenarios 2025 (ED1 data table) and Ten Year Outlook 2026; Ofgem connections review, February 2026; S&P Global, October 2026; manufacturer order books reported in 2026. Details and links are in the audit report.

Open the explorer

How big is the gap?

The explorer opens on current policy: the Clean Power 2030 wind, solar and battery build and NESO’s renewables beyond it, Sizewell C and the planned Wylfa reactors, batteries and trade with Europe, and a gas fleet kept near today’s 35 GW by building about 25 replacement combined-cycle stations as older plants retire. The government would add supply to this, but at the moment only what is planned is in this model and demonstrates the shortfall and lack of urgency in current planning.

Extra firm power needed to meet the 3-hour reliability standard

Gap = the gas-engine capacity that, added to current policy, brings expected shortfalls down to the 3-hour standard. It is the capacity needed whatever the build time; plants ordered from 2029 cannot all arrive in time for the early 2030s.

Central demand: the standard is missed from 2031, and in 20 of the 21 years to 2050. Britain is about 6 GW short in 2035, 19 GW in 2040 and 32 GW in 2050. Expected supply shortfalls rise from about 19 hours a year in 2035 to 185 hours in 2050, against a standard of 3.
Range: 27 GW short by 2050 with lower demand, 42 GW with higher demand.

More renewables?

Based on current policy and the 95% clean target the government will build more wind and solar. We tested this in the 'current policy with 25% more' model (about 73 GW more by 2050), and 50% more, which could not be built in time but shows the limit. Central demand:

	Current policy	+25% wind and solar	+50% (not deliverable)	Renewables + gas
Expected shortfall, 2050 (standard 3 hours)	185 h	95 h	60 h	Under 3 h
Firm power still needed, 2050	32 GW	27 GW	22 GW	None
Meets the standard?	No, from 2031	No, from 2031	No, from 2034	Yes
Cost 2030–50 (real 2024 £)	£1,179bn	£1,312bn	£1,452bn	£1,205bn
CO₂ 2030–50	689 Mt	640 Mt	613 Mt	718 Mt

More renewables cut the shortfall, but each 100 GW of extra wind and solar replaces only about 5–7 GW of firm power. About 87% of the extra output in 2050 arrives when there is already a surplus and is curtailed. The hours that remain short are cold, still spells, when extra turbines add little. Meeting the standard therefore still needs firm power, and gas does it for about £26bn more than current policy.

Caveat. More interconnection, storage and flexible demand would let more of the surplus be used. They add costs the model does not include (as do grid connections for the extra wind and solar), and in Europe-wide cold, still spells neighbouring countries have less to spare: the government's expert panel on NESO's 2026 capacity report identifies low wind with high European demand as "evidently the key risk case for GB" (Panel of Technical Experts, 2026, para. 107).

The explorer then shows two ways of providing that firm power. Renewables + gas keeps current policy's renewables and adds the gas needed to keep the lights on and meet the 3-hour reliability standard. Existing plants are kept longer, then new engines, open-cycle and combined-cycle plants are added. The nuclear buildout keeps the renewables already built or contracted but adds no more, building a fleet of small modular reactors and one large reactor, with coal and gas backup. Both are sized to the same standard.

Solving the problem

We are so far behind in energy generation, that this problem cannot be solved by supply side changes alone. We are simply too far behind to be pursuing EV targets for vehicles and converting to heat pumps whilst supporting an industrial strategy and widespread AI adoption. Priority to AI buildout and economic growth has to come above other demands for power generation. These models assume there is at least some reform to improve the current planning timelines.

How much AI demand are we planning for?

The programme demand case plans for about 97 TWh a year of data-centre demand by 2035: NESO’s central 37 TWh plus 60 TWh more, or about 11 GW running day and night. It is a planning choice, not a forecast, and it is above every NESO estimate. The gap chart above uses NESO’s own pathways, so the finding that current plans fall short does not depend on it.

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 97 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 programme demand case	97 TWh	2035
LSE high case, 20 GW at 90%	about 158 TWh	—

Why we picked 97 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.
The reforms are designed to attract computing investment, through faster connections and routes for large loads to bring their own power. 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.

The 60 TWh step is a round planning increment, not derived from any one source, and full effect by 2035 is ambitious given connection and equipment lead times. It would make data centres about 22% of British electricity demand in 2035, a similar share to Ireland today and above the 9.5–15% US federal researchers project for the US in 2030; some US forecasters also judge utility projections to be overstated. Treat 97 TWh as the upper planning case; the explorer shows NESO’s lower pathways alongside it. Sources: DSIT, UK Compute Roadmap, July 2025, section 4.2; LSE CETEx written evidence DCU0046; NESO Future Energy Scenarios 2025; NESO, Ten Year Outlook 2026 briefing to the Electricity Markets Advisory Council, 22 September 2026 (slides 15–17); BloombergNEF via Utility Dive, December 2025; NERC Long-Term Reliability Assessment, January 2026; Grid Strategies, National Load Growth Report 2025; LBNL, US Data Center Energy Usage Report, June 2026.

Using the explorer: what is instant and what needs a run

Instant

About 50 fully calculated plans: current policy, current policy with 25% more renewables, renewables and gas, the nuclear buildout and the 95% clean experiment, under four demand pathways and several delivery settings. The explorer opens on current policy.
For each, year by year to 2050: capacity, generation, imports, fuel use, emissions, costs, supply checks across seven weather years and two cold-spell stresses, and hours against the 3-hour reliability standard.
If you edit a plan's build orders, its fleet, construction timetable and construction spending update immediately.

Needs a model run

Hour-by-hour results for an edited plan: generation, shortfalls, reliability hours, fuel, emissions and running costs.
These show as "Hourly recalculation required", so out-of-date figures are never displayed.
You can save an edited plan from the explorer as a file and open it again later. I may add the python script later so users can build their own plans and save.

What the delivery setting means

The two plans that add firm power, Renewables + gas and the nuclear buildout, can be built in different ways. Step 3 in the explorer chooses how:

Official standard (the default): the gas fleet is sized to meet the 3-hour reliability standard, within limits on how fast equipment can be delivered.
Tight equipment market: as Official, but with scarce, more expensive turbines and engines.
Planning case: existing gas kept for five years after inspection, and limited new equipment deliveries.
Stronger retention: existing gas kept for ten years, with a second overhaul.
Faster delivery: more new equipment each year.

Current policy, +25% renewables and the 95% clean constraint add no firm power beyond like-for-like gas replacement, so there is nothing for the setting to change and it is greyed out.

Explore the model

Start from current policy and its gap, then compare renewables and gas with the nuclear buildout across four demand pathways: capacity, generation, costs and security of supply, including the 3-hour reliability standard.

Open the explorer

Methods and evidence

The audit report sets out every method, source and assumption. The workbook lists the inputs and results.

Audit report Workbook