How our numbers are worked out

The live generation mix is built from Elexon's FUELINST feed, which publishes metered output by fuel type roughly every five minutes for every large power station connected to the high-voltage transmission network in Great Britain.

We add up the published rows into the categories you see: wind, gas, nuclear, biomass, hydro, coal, oil and other. Nothing is scaled, smoothed or normalised, and there is no balancing row to make the totals look neat. Coal and oil are hidden when they are exactly zero, which is most of the time.

Percentages always come from the same snapshot as the megawatts beside them, and always use one denominator. We never take a percentage from one dataset and place it next to megawatts from another.

FUELINST only sees power stations connected to the transmission network. Most solar farms and many wind farms in Britain are connected to local distribution networks instead, so they are invisible to that feed. FUELINST publishes no solar row at all.

For solar we therefore use NESO's own estimate of embedded solar output for the current half hour, taken from the Demand Data Update. If NESO's estimated outturn is not yet available we use its forecast for that half hour and label it as a forecast. Because this plant is not in FUELINST, adding it cannot double count anything.

For wind we show the metered transmission-connected total plus NESO's estimated embedded wind, and the figure is labelled to say so. You can open the wind entry to see the two parts separately. If NESO's estimate is missing we show only the metered figure rather than treating the unknown part as zero.

“Other” is Elexon's own residual fuel category. It covers metered generation that does not fall into the named fuel types, such as smaller or mixed-fuel plant and some waste and landfill gas units. We pass it through exactly as published rather than guessing what sits inside it.

It is normally a small share of the total. If it ever looks large, that is what the official feed reported for that five-minute period.

The headline on the live electricity section is a simple identity: everything being used in Britain right now has to come from somewhere.

Electricity supplied = generated in Britain + net transfers

Net transfers is a single signed figure: the net flow across the subsea and undersea cables plus the net position of pumped storage. Imports and storage generating are positive; exports and storage charging are negative. If the combined figure is negative it is shown with a minus sign; we never reword it to hide the direction.

We deliberately do not use the official transmission-boundary demand figure as the denominator for the mix. That figure nets off embedded generation, so it measures a different boundary from the metered components shown here and would leave a permanent gap that no row on the page explains. Where the official demand figure is available we show it separately as context.

Pumped storage is the only component that regularly runs in both directions, so it always carries a sign.

• Positive means the stations are generating, releasing water downhill and putting power onto the grid.
• Negative means they are charging, using power to pump water back uphill. Charging is consumption, not generation.

Because of this, storage is never counted inside the renewable or low-carbon share. Those shares are worked out from generation only: renewables are wind, solar and hydro; low carbon adds nuclear and biomass. Both are expressed as a share of what Britain generated in the same snapshot, so they can never disagree with the mix shown beneath them.

Flows on the cables linking Britain to its neighbours come from the interconnector rows of the same five-minute Elexon feed used for generation, so the two always describe the same instant.

The rows are mapped to named cables and countries:

• France: IFA, IFA2, ElecLink
• Norway: North Sea Link
• Denmark: Viking Link
• Netherlands: BritNed
• Belgium: Nemo Link
• Ireland: East-West, Greenlink
• Northern Ireland: Moyle

Each cable keeps its sign: positive when Britain is importing, negative when exporting. Cables are then grouped by country for display, and the country totals are simply the sum of their cables. A country can import and export at the same time on different cables, and the grouping shows the net position.

A snapshot is only used when enough of the known cables are present. An incomplete or missing snapshot is never treated as zero flow.

Different sources publish at different speeds: the generation feed every five minutes or so, the gas flow data every twelve, and settlement-based series hours later. We therefore hold three rules.

• One snapshot, one moment. A source is only combined with the others when its observation time is within 30 minutes of them. Anything outside that window is excluded and listed with the reason, rather than quietly mixed in.
• Missing is never zero. If a source cannot be retrieved we keep the last good reading for a short period and mark it as delayed. After that it becomes unavailable and the affected figures disappear instead of reading as zero.
• The time you see is real. Update times are the publication or observation times of the data itself, not the time your browser loaded the page.

Live gas comes from National Gas Transmission's instantaneous flow data, which reports each entry point onto the national transmission system in millions of cubic metres per day, updated roughly every twelve minutes.

Gas demand, gas supply and linepack are National Gas's own published totals. The balance shown is supply minus demand, and it is only calculated when both readings come from within five minutes of each other.

The individual entry points are ours to group, and we group them by where the gas comes from: Norwegian pipelines, LNG terminals, UK production, European pipelines, storage sites and other entry points. The underlying site names, categories and observation times are shown when you open an entry, so you can always see which sites sit in which group.

Linepack is shown separately, because it is not a flow. It is the amount of gas held in the pipes themselves at that moment, and it rises and falls through the day as supply runs ahead of or behind demand.

All price cap figures are read from Ofgem's published “Final levelised cap rates model” workbook for each quarterly charge restriction period. We do not recalculate the cap.

Rates are stored as pence per kWh and pence per day at full precision, and rounded only when displayed. Every rate is specific to a region, a payment method and a meter type, because the cap differs on all three. Prices shown include VAT.

Annual cost = unit rate × annual kWh + standing charge × 365

A typical annual bill uses Ofgem's own typical domestic consumption benchmark for electricity and gas. It is an illustration for a household using that much energy, not a prediction of your bill. The cap limits unit rates and standing charges, not the total you pay.

Where the next cap period has been announced, we show the announced rates and the change against the current period. Anything not yet announced by Ofgem is not shown.

Most live figures on this site cover Great Britain, England, Scotland and Wales, because that is one electricity system with one set of operational data, run by NESO and settled through Elexon.

Northern Ireland is part of the United Kingdom but not of the GB electricity system. It shares the Single Electricity Market with Ireland and has its own regulator, so its generation and prices are not included in the live GB figures. The Moyle cable appears here only as a flow into or out of Britain.

The Ofgem energy price cap likewise applies to England, Scotland and Wales only. Northern Ireland has separate arrangements under its own regulator.

Some datasets, particularly project and capacity records from government, are published on a UK-wide basis. Where a figure covers the UK rather than Great Britain, we say so on the figure itself.