System architecture
How does energy flow through six layers from source to socket?
The GB energy system is a stack. Primary energy enters at the top, passes through conversion, transmission, distribution, and consumption, and is reconciled through market settlement at the bottom. Each layer has different operators, different regulators, and different technical constraints. This page maps the full stack.
What are the six layers of the GB energy system?
Energy flows downward through six layers. Each layer has its own operators, regulators, and technical characteristics. Market and settlement data flows back upward, closing the loop.
What passes between each layer?
Each layer boundary is a real interface where information, energy, or authority changes hands. These are the signals and instruments that cross each boundary.
| Interface | What crosses the boundary |
|---|---|
| Layer 6 (Policy) ↔ Layer 5 (Governance) | Carbon budgets, statutory net zero targets, legislative instruments (Energy Act 2023, Climate Change Act 2008) |
| Layer 5 (Governance) ↔ Layer 4 (Market) | Licence conditions, price cap methodology, industry codes (BSC, CUSC, Grid Code, DCUSA) |
| Layer 4 (Market) ↔ Layer 3 (Operations) | Gate closure (1 hour ahead), dispatch instructions, BM bids and offers, imbalance settlement |
| Layer 3 (Operations) ↔ Layer 2 (Network) | SCADA telemetry, protection relay settings, 132 kV transmission/distribution boundary (14 DNO licence areas, 318 GSPs) |
| Layer 2 (Network) ↔ Layer 1 (Physical) | Voltage regulation (400 kV to 230 V), fault current limits, thermal ratings, power quality standards |
What happens at each layer?
Click any layer to expand its detail card. Each card covers the key assets, operators, statistics, and interface to the next layer.
Primary Energy Sources
All energy in the GB system originates from a primary source: fossil fuel (gas, coal, oil), nuclear fission, renewable generation (wind, solar, hydro, biomass), or imports via interconnectors. The generation mix has shifted substantially since 2010, with coal falling from 28% to below 1% and wind rising from 3% to over 25% of annual output.
Key assets
- Fossil fuel: CCGT fleet (Drax, Pembroke, Carrington), remaining OCGT peakers
- Nuclear: Hinkley Point B (closing), Sizewell B, Hinkley Point C (under construction)
- Renewables: Hornsea, Dogger Bank, East Anglia offshore clusters; onshore wind predominantly Scotland
- Imports: IFA, BritNed, Nemo, NSL, Viking, ElecLink and others via subsea HVDC cables
Interface to Layer 2
Primary energy is converted into electricity at power stations or processed at gas terminals. The output connects to the transmission system at 400 kV or 275 kV, or to the distribution system at 132 kV and below for smaller generators.
Conversion and Processing
This layer converts primary energy into a form that can be transported and used. Gas-fired power stations convert natural gas into electricity. LNG terminals regasify imported liquefied natural gas. Nuclear stations convert fission heat into steam-driven electricity. Emerging hydrogen production facilities (electrolysis and reforming with carbon capture) sit here as the hydrogen economy develops.
Key assets
- Power stations: CCGT fleet provides the largest single block of dispatchable capacity
- LNG terminals: Milford Haven (South Hook, Dragon), Isle of Grain
- Gas processing: St Fergus terminal (North Sea gas landing), Easington, Bacton
- Hydrogen pilots: HyNet (North West), East Coast Hydrogen, Acorn (St Fergus)
Interface to Layer 3
Converted electricity enters the transmission network at high voltage. Processed gas enters the National Transmission System. Both energy vectors flow through separate but parallel bulk transport networks.
Transmission Networks
The transmission network carries bulk energy over long distances. For electricity, this means the 400 kV and 275 kV overhead lines and underground cables operated by three transmission owners. For gas, it means the National Transmission System of high-pressure mains. NESO (the National Energy System Operator) manages real-time balancing and system security across both.
Key functions
- Balancing: NESO dispatches generation up and down in real time to match demand second by second
- Frequency response: Mandatory and commercial services keep the system within 49.5 to 50.5 Hz
- Voltage management: Reactive power and transformer tap changers maintain voltage within limits
- Congestion management: Constraint payments resolve transmission bottlenecks, particularly the B6 Scotland-England boundary
- Interconnectors: 10 subsea HVDC links connect GB to France, Belgium, Netherlands, Norway, Denmark, and Ireland
Interface to Layer 4
Energy steps down from transmission to distribution at Grid Supply Points (GSPs). There are approximately 330 GSPs in GB, each feeding a distribution area. The 132 kV boundary is classified as transmission in Scotland and distribution in England and Wales.
Distribution Networks
Distribution networks carry energy the final miles to consumers. Electricity distribution operates at 132 kV (in England and Wales), 33 kV, 11 kV, and 400/230 V. Gas distribution operates at lower pressures through regional mains. Smart meters sit at the interface between distribution and consumption, providing half-hourly data that feeds settlement and network planning.
Key operators
- UK Power Networks: South East, East, London (3 licence areas)
- National Grid Electricity Distribution: West Midlands, East Midlands, South Wales, South West (4 licence areas)
- Northern Powergrid: North East, Yorkshire (2 licence areas)
- Electricity North West: North West (1 licence area)
- SP Energy Networks: South Scotland, Merseyside/North Wales (2 licence areas)
- SSEN Distribution: North Scotland, Southern England (2 licence areas)
- Gas Distribution Networks: Cadent, SGN, NGN, WWU (8 GDN areas across 4 groups)
Interface to Layer 5
Distribution networks deliver energy to consumer premises via service connections and meters. The smart metering rollout provides the data link that connects physical consumption to the settlement and market layers above.
Consumption and Response
This is where energy is used. Historically, consumption was passive: consumers drew power and paid a bill. The transition to net zero is making this layer active. Heat pumps, electric vehicles, battery storage, and smart tariffs are turning consumers into participants who can shift, store, and export energy. Demand-side response is becoming a system resource, not an afterthought.
Consumer segments
- Domestic: 29 million households, majority on single-phase 230 V supply, average consumption approx. 2,900 kWh/year
- Industrial and commercial: Large users on HV or EHV connections, many with half-hourly metering and access to wholesale markets
- Prosumers: Growing segment with rooftop solar, battery storage, and export capability via Smart Export Guarantee
- Flexibility providers: Aggregators, battery operators, and demand response platforms participating in balancing and capacity markets
Feedback to system
Metering data flows upward from consumers through data collectors to Elexon for settlement. Price signals from time-of-use tariffs and flexibility contracts create a feedback loop that shapes when consumers use energy and when they export or store it.
Market and Settlement
The market layer reconciles physical energy flows with financial flows. Every unit of electricity generated, consumed, or traded must be settled. The Balancing and Settlement Code (BSC), administered by Elexon, governs how this works. The wholesale market sets the price, the balancing mechanism handles real-time imbalances, and network charges (TNUoS, DUoS, BSUoS) recover the cost of operating the physical infrastructure.
Market mechanisms
- Wholesale market: Day-ahead and intraday trading on EPEX SPOT and N2EX, plus bilateral OTC contracts
- Balancing mechanism: NESO accepts bids and offers from generators in real time to balance supply and demand
- Capacity market: Annual auctions procure firm capacity to ensure security of supply four years ahead
- Contracts for Difference: CfD scheme provides long-term revenue certainty for renewable generators against a strike price
- Network charges: TNUoS (transmission), DUoS (distribution), BSUoS (balancing system) charges recover infrastructure costs
- Regulation: Ofgem sets price controls (RIIO), enforces licence conditions, and oversees code governance
Upward feedback
Settlement data and price signals flow upward from Layer 6 to every other layer. Wholesale prices inform generator dispatch decisions. Network charges influence where new capacity connects. Capacity market results shape investment in firm generation and storage.
How big is the GB energy system?
These numbers give a sense of the physical and institutional scale of the system. Each figure carries its own set of engineering, regulatory, and commercial implications.
Why six layers and not five or seven?
The six-layer model maps to the physical flow of energy and the institutional boundaries. Generation, conversion, transmission, distribution, consumption, and settlement each have different operators, regulators, and technical constraints. You could collapse generation and conversion into one layer, or split settlement from market trading, but the six-layer model reflects how the system is actually governed. Each layer boundary corresponds to a real organisational handoff, a change in regulatory regime, or a physical transformation of the energy carrier.
How do market signals flow upward?
Settlement data from meters flows upward through Elexon to generators and the system operator. Price signals from the wholesale market inform generator dispatch decisions and investment. Network charges signal where capacity is needed and where constraints exist. Capacity market results shape whether new gas peakers, batteries, or interconnectors get built. The system is a loop: physical energy flows downward and financial and data signals flow upward. Neither direction works without the other.
Current position
The layers are tightly connected in practice. Changes in physical assets or demand patterns often cascade into market outcomes, data requirements, operational procedures, and governance changes. Looking at the layers together helps explain why apparently simple reforms usually touch several parts of the system at once.
Why this matters now
Distribution networks now sit at the centre of many transition pressures because heat pumps, electric vehicles, rooftop solar, batteries, and most new local flexibility connect there. That is why visibility, active network management, data publication, and local reinforcement are becoming more prominent in current regulatory and investment programmes.
Methodology and sources
Last reviewed: 17 March 2026
This page maps the six-layer architecture of the GB energy system using official operator data, regulatory publications, and settlement documentation. Capacity figures are approximate and based on the most recent published data at the time of review.
Next route
How is the system operated day to day?
From NESO control rooms to automated frequency response. Understand the operating model that keeps the lights on.