Electricity domain
Electricity Markets
How electricity is bought, sold, balanced, and settled. The market structure that turns physics into money.
The three-stage market
Electricity trading happens in three distinct stages before physical delivery. Each stage has different timeframes, participants, and price mechanisms. Understanding which stage you are talking about is essential when discussing UK electricity pricing.
After forward trading closes, reality intervenes. Wind forecasts update, demand surprises, generators fail. NESO accepts final bids and offers to balance the system in real-time.
The gate closure process
- T-1 hour: Gate closes for physical trading. NESO knows the generation and demand forecast.
- T-60 to T-5 minutes: Participants submit bids (reduce generation) and offers (increase generation) to NESO
- T-5 to T-0 minutes: NESO runs algorithms to select cheapest bids and offers to balance
- T+30 min (after delivery): Elexon calculates imbalance prices based on what NESO accepted
After electricity is delivered, Elexon calculates who owes what. Every generator, supplier, and trader settles their half-hourly positions. The process takes up to 14 months because metered volumes must be reconciled against contracted positions for every half-hour.
Settlement mechanics
- Physical reconciliation: Metered generation and demand are compared
- Imbalance price calculation: Elexon publishes the System Price (SYS) and Imbalance Price (Exh, Inl) for each half-hour
- Who profits: Generators short (underproduced) pay Exh; generators long (overproduced) pay Inl
- Billing: Suppliers receive customer meter data from DNOs; they invoice consumers monthly
How electricity prices form
A wholesale electricity price is not a single thing. It is the sum of multiple costs and conditions. Understanding the price stack helps explain why electricity is sometimes free and sometimes costs GBP 500/MWh.
Why prices vary by generation type
Different generators have different cost stacks. Understanding this explains why wind runs at any price and gas is the marginal (price-setting) generator most of the time.
Behaviour: Runs whenever wind blows
Price impact: Drives prices down; goes first when spot price too low
Behaviour: Sets the price 70% of the time
Price impact: Most responsive to demand
Behaviour: Runs baseload always
Price impact: Reduces need for expensive peak generation
Market mechanisms
The eight main market mechanisms that coordinate electricity trading in GB. Each has a specific function and participant base.
Wholesale market
Day-ahead and intraday trading of physical electricity. Prices set by supply and demand; most transparent market.
Participants: Generators, suppliers, traders, large industrial consumers
Volume: Approx 70% of GB demand is hedged in forward market; 20% day-ahead; 10% intraday and spot
Balancing Mechanism
NESO's tool for real-time balancing. Generators and flexible resources submit bids and offers to adjust generation in the last hour before delivery.
Participants: Large generators, battery storage, demand-side response providers
Cost: GBP 2-5 billion annually depending on wind forecast errors and demand volatility
Settlement
Elexon calculates financial positions for all market participants. Every half-hour, generation and demand are reconciled; imbalance prices are set.
Administrators: Elexon (BSC Administrator); all participants must comply with Balancing and Settlement Code
Imbalance pricing: Penalises participants who do not balance themselves; rewards those who forecast accurately
Contracts for Difference (CfD)
Government guarantees a floor price for renewable electricity. If wholesale price falls below the strike price, government pays the difference. If price exceeds strike, generator pays back.
Eligibility: Wind, solar, tidal, nuclear, biomass
Strike prices (recent): Onshore wind GBP 45/MWh, solar GBP 40/MWh, offshore wind GBP 55/MWh
Capacity Market (CM)
Annual auction paying capacity providers (generators, storage, demand response) to ensure supply security. Payment is per derated MW regardless of whether the plant runs.
Duration: Typically 1-year or 15-year contracts; winners must be available next winter
Recent clearing price: GBP 25-35/kW/year for thermal; GBP 15-20/kW/year for renewable with CfD
Ancillary services
NESO buys frequency response, reactive power, and inertia to maintain system stability. Not about energy; about grid services.
Services: Fast Frequency Response (FFR), Enhanced Frequency Response (EFR), Reactive power, Inertia, Reserve
Annual cost: Approximately GBP 400-600 million
Network charging (TNUoS, DUoS, BSUoS)
Users of the grid pay network operators for transmission and distribution infrastructure. Three main charges.
TNUoS: Transmission charges; generators and large consumers pay to use 400kV/275kV backbone
DUoS: Distribution charges; all consumers pay local DNO for 33kV-230V networks
BSUoS: Balancing Services charge; all consumers pay NESO for system balancing cost
REMA (Review of Electricity Market Arrangements)
Government review of GB electricity market launched 2023. Aims to make market fit for net-zero. Status: Phase 2 underway.
Key proposals: Nodal pricing (replace TNUoS), long-term CfD contracts, storage incentives, demand response framework
Timeline: Consultation 2024, implementation 2026-2028
Key market participants by role
Understanding who makes money from which mechanism is essential to understanding incentives in the market. Each participant has a different business model.
Revenue streams: Wholesale market sales, Contracts for Difference (CfD), Capacity Market payments, Balancing Mechanism, Ancillary services, constraint payments from NESO. Example: A 100 MW gas plant earns GBP 20M wholesale, GBP 15M capacity, GBP 2M ancillary, GBP 1M constraints = roughly GBP 38M gross annually before operating costs.
Revenue streams: Markup on wholesale electricity, standing charges, network pass-through. Margin is typically GBP 20-40/year per household in a competitive market. Risk: If they buy wholesale at GBP 50/MWh but retail price cap only allows GBP 35/MWh, they lose money. 2021-2023 was catastrophic for suppliers.
Business model: Buy low (forward market, winter), sell high (spot market, peak hours). Provide liquidity. Example: Buy winter quarter forward at GBP 45/MWh, then sell day-ahead at GBP 52/MWh during peak demand; pocket GBP 7/MWh spread.
Power: Can dispatch any generator or flexible resource to balance the system. Pays for balancing services and imbalance settlement. Incentive: Minimise cost; NESO has no financial profit motive (public entity). BSUoS charge to consumers funds NESO operations and balancing costs.
Function: Calculates imbalance prices, settles all market participants half-hourly, manages Balancing and Settlement Code rules. Data: Publishes all settlement data via BMRS (Balancing Mechanism Reporting Service) which is open to the public and used extensively by traders, analysts, and researchers.
What is the difference between wholesale price and retail price?
The wholesale price is what generators and suppliers trade at on exchanges and bilateral contracts. The retail price is what you pay on your bill. Retail includes wholesale cost plus network charges (20-25%), policy costs (environmental levies, CfD payments), supplier margin, and VAT. The price cap limits the total retail price for standard tariffs.
Why does the balancing mechanism cost so much?
The Balancing Mechanism cost 7.2 billion pounds in 2024 because constraint management is expensive. When too much wind generation in Scotland cannot flow south due to transmission bottlenecks, NESO must pay Scottish wind farms to turn off and pay gas plants in England to turn on. This is not a market failure; it is a network capacity problem that can only be solved by building more transmission lines.
Methodology and sources
Last reviewed: 17 March 2026
Market structure and mechanisms described here reflect the current GB electricity market as of March 2026. Price examples are illustrative. Live data is available on the Live Dashboard page.
| Source | Elexon BMRS - Live market data, settlement, and balancing costs. |
| Source | Ofgem price cap - Retail price methodology and quarterly updates. |
| Source | Low Carbon Contracts Company - CfD allocation results and strike prices. |
| Source | EMR Delivery Body - Capacity Market auction results and clearing prices. |