The GB Electricity System: Reference Data

Last updated: March 2026 Coverage: Most data is calendar year 2025 unless otherwise stated. All figures relate to Great Britain (England, Wales, Scotland) unless marked "UK" (which includes Northern Ireland).

1. Generation Mix

Installed Capacity

Wind capacity reached 33 GW total in Q3 2025, a 4% year-on-year increase. Solar grew 18% year-on-year to 21 GW. (Source: DESNZ Energy Trends, Dec 2025)

Electricity Generation (2025)

2025 was the first full calendar year with zero coal generation, following the closure of Ratcliffe-on-Soar in September 2024.

Capacity Factors (derived, 2025)

Note: Nuclear capacity factor was unusually low in 2025 due to AGR outages. Sizewell B alone achieved 99% load factor and generated 10.4 TWh. (Source: EDF fleet update, Jan 2026)

2. Demand

Demand grew for the second consecutive year after roughly two decades of decline.

Electrification Projections

3. Grid

Transmission Network Structure

The GB transmission network is operated by three Transmission Owners (TOs): - National Grid Electricity Transmission (NGET) -- England and Wales - SP Energy Networks (SPT) -- central and southern Scotland - SSEN Transmission (SHE-T) -- northern Scotland and islands

NESO (the system operator) coordinates dispatch and balancing across all three areas.

Key Constraints

The dominant constraint is the Scotland-England boundary (B6). Scottish generation capacity is approaching 20 GW today and is set to reach ~45 GW by 2030 under NESO's central transition pathway. Wind farms in Scotland have grown 50% since 2020, far outpacing transmission reinforcement. (Source: NESO Clean Power 2030 report, Dec 2024)

Key reinforcement projects: - Eastern Green Link 1 (EGL1): 2 GW subsea HVDC, Scotland to northeast England. Critical for 2030 targets. - Eastern Green Link 4 (EGL4): additional subsea capacity in development.

Balancing Costs and Curtailment

76% of constraint costs relate to gas generators being paid to increase output to replace curtailed renewables. (Source: NESO Annual Balancing Costs Report, Jun 2025)

Network Reliability

Transmission network reliability exceeded 99.9% in each year from 2021 to 2024. (Source: DESNZ Security of Supply Report 2025)

4. Market Structure

Wholesale Market

The GB wholesale electricity market operates under BETTA (British Electricity Trading and Transmission Arrangements), which has been in place since April 2005. It extended the earlier NETA arrangements to include Scotland.

How it works: 1. Forward/futures market -- Bilateral contracts traded months or years ahead. Front-quarter churn rate: ~3x (liquid market threshold). Bid-offer spreads: ~£0.4/MWh. Jan-Mar 2025 traded volumes: ~250 TWh. (Source: DESNZ Security of Supply Report 2025) 2. Day-ahead market -- Power exchanges (e.g. N2EX, EPEX) clear next-day positions. 3. Balancing Mechanism (BM) -- NESO's real-time tool. Generators submit bids and offers for each half-hour settlement period. NESO dispatches in merit order (cheapest first) to balance the system. 4. Imbalance settlement -- Parties whose actual position differs from contracted position pay/receive the system price, managed by Elexon under the Balancing and Settlement Code (BSC).

The wholesale price is set by the marginal generator -- in practice, usually a gas plant. This is why gas prices drive electricity prices even when renewables supply almost half of generation.

Capacity Market

The Capacity Market pays generators (and demand-side response) a fixed £/kW/year to be available during periods of system stress. Auctions run four years ahead (T-4) and one year ahead (T-1).

Forward-looking capacity procured: - 2026/27: 50.1 GW total de-rated capacity secured - 2027/28: 54.1 GW - 2028/29: 56.1 GW

(Source: DESNZ Security of Supply Report 2025)

De-rated margin for winter 2025/26: 6.1 GW (10.0% of average cold spell peak demand), with a Loss of Load Expectation below 0.1 hours/year. (Source: DESNZ Security of Supply Report 2025)

Contracts for Difference (CfD)

CfDs are the government's main mechanism for supporting new low-carbon generation. The generator receives a guaranteed "strike price" -- if the wholesale price is below the strike price, the government pays the difference; if above, the generator pays back.

5. Key Institutions

6. Prices

Wholesale Electricity Prices (2025)

Prices rose in early 2025 due to colder weather and reduced wind output, which increased gas-fired generation.

Retail Prices (Household, Electricity Only)

Typical dual-fuel annual bill (direct debit): ~£1,720/year as at Q3 2025 price cap. (Source: Ofgem)

Bill Breakdown (Electricity, Q1 2026 Price Cap)

VAT on domestic energy is charged at 5%.

7. Emissions

Grid Carbon Intensity

The slight increase in 2025 was driven by higher gas generation (+5%) and lower nuclear output (-12%), despite record renewables. 2025 was the first full year with zero coal generation. (Source: Carbon Brief, Jan 2026)

International Comparison

France's low intensity reflects its ~70% nuclear generation. GB performs well against the EU average but has roughly double France's intensity. (Source: Ember European Electricity Review 2025)

Trajectory

Peak renewable generation hit 31.3 GW on 4 July 2025. The grid operated at 97.7% zero-carbon for 30 minutes on 1 April 2025 and logged 87 hours of effectively 100% clean power through the year (accounting for exports). (Source: NESO 2025 Review; Carbon Brief)

8. Security of Supply

Gas Supply

GB has eight gas storage sites with the Rough offshore facility (reopened Oct 2022) providing roughly half of total storage capacity. Total storage is small by European standards -- approximately 1.5-1.7 bcm compared to Germany's ~24 bcm. (Source: Ofgem GB Gas Storage Facilities 2025; Energy UK)

Electricity Interconnectors

(Source: DESNZ Security of Supply Report 2025 -- reports 10.3 GW across ten interconnectors including both Irish links)

Under construction: NeuConnect to Germany, 1.4 GW, expected 2028.

2030 target: 12-14 GW of interconnector capacity. (Source: DESNZ Security of Supply Report 2025)

Net electricity imports in 2024: 33.4 TWh (+40% on 2023). (Source: DESNZ Security of Supply Report 2025)

9. Connection Queue

The pre-reform queue of ~739 GW was roughly four times what GB needs to meet its 2030 clean power goals. NESO has shifted to a "first-ready, first-needed, first-connected" model. Projects must demonstrate land rights, planning permission, and alignment with strategic energy needs to receive a connection offer. Ofgem gave in-principle approval to reforms in February 2025. (Source: BCG report, Sep 2025; Greenberg Traurig, Apr 2025; NESO)

10. Nuclear Fleet Status

Operational Stations (as of early 2026)

Total operational: ~5.9 GW (but effective output well below this due to outages on ageing AGRs -- 2025 generation was just 36 TWh, lowest in half a century).

New Build

Government target: 24 GW of nuclear capacity by 2050. (Source: World Nuclear Association)

11. Battery Storage

Sources

All numbers above are individually sourced. The main reference documents used:

• DESNZ, Digest of UK Energy Statistics (DUKES) 2025, Chapters 1, 4 and 5 (Jul 2025)
• DESNZ, Energy Trends December 2025 (Dec 2025)
• DESNZ, Statutory Security of Supply Report 2025 (2025)
• DESNZ, Contracts for Difference and Capacity Market Scheme Update 2025 (2025)
• DESNZ, CfD Allocation Round 7 Results (Jan 2026)
• NESO, Britain's Energy Explained: 2025 Review (Jan 2026)
• NESO, Clean Power 2030 Report (Dec 2024)
• NESO, Annual Balancing Costs Report (Jun 2025)
• Ofgem, Energy Price Cap quarterly updates (2025)
• Ofgem, GB Gas Storage Facilities 2025 (Jan 2025)
• Carbon Brief, Analysis: UK renewables enjoy record year in 2025 (Jan 2026)
• Ember, European Electricity Review 2025 (2025)
• Nesta, What's in an Energy Bill? (updated Nov 2025)
• IEA, Electricity Mid-Year Update 2025 (2025)
• EDF, Fleet Update (Jan 2026)
• World Nuclear Association, United Kingdom profile (2025)
• BCG, Mind the Queue: Connection Reform for the Electricity Grid (Sep 2025)