Glossary
The GB electricity system, in plain English
The grid runs on jargon - 27 of its most load-bearing terms, defined honestly and linked to where each number shows up live on the dashboard.
All terms
- Balancing Mechanism (BM)
- how NESO matches supply and demand second-by-second: it accepts bids (an instruction to turn down) and offers (turn up) from BM Units. Elexon BOALF = the acc...
- BESS
- Battery Energy Storage System. Discharge appears inside Elexon's OTHER/Misc; if shown separately it must be subtracted from OTHER to avoid double-counting.
- BM Unit (BMU)
- A registered unit (often a single generator or station) in the Balancing Mechanism. B1610 reports output per BMU, which is how you get per-station live MW fo...
- BMRS
- Balancing Mechanism Reporting Service. Elexon's data service. The modern, key-free API is the Insights Solution at data.elexon.co.uk.
- Carbon intensity
- gCO₂ per kWh of electricity. The Carbon Intensity API gives a national figure plus a forecast and an index band (very low → very high).
- CCGT / OCGT
- Combined-Cycle / Open-Cycle Gas Turbine. CCGT is the efficient, workhorse gas plant; OCGT is a fast-start peaker. Both roll up into "Gas".
- Curtailment
- a generator (typically wind) instructed below its notified plan - "paid to switch off" - usually because the grid can't carry its output (a network constrain...
- DNO region
- Distribution Network Operator area. The Carbon Intensity API's regional endpoints break GB into 14 DNO regions (modelled, not metered).
- Elexon
- Administers the Balancing and Settlement Code; runs the wholesale market settlement and publishes BMRS data. Source of metered MW and interconnector flows.
- Embedded (distributed) generation
- Generators connected to the distribution network (local, lower-voltage), not the high-voltage transmission network. The system operator has no real-time mete...
- GB vs UK
- This data covers Great Britain (England, Scotland, Wales). Northern Ireland is a separate market (SEM) and only appears here as an interconnector (Moyle). Sa...
- Generation mix
- The share of each fuel/technology generating right now. The Carbon Intensity API gives it as percentages, embedded-inclusive.
- Grid frequency
- the AC grid's frequency in hertz; GB targets 50.00 Hz. It rises when generation exceeds demand and falls when demand exceeds it, so it's a live balance signa...
- Imbalance / cash-out price
- the £/MWh price the operator charges or pays parties who were out of balance in a settlement period. Since the P305 reform a single price applies in both dir...
- INDO / NDF
- Initial National Demand Out-turn / National Demand Forecast. "Net" national demand: metered generation minus station load, pumped-storage demand and intercon...
- Interconnector
- A subsea/cross-border cable linking GB to another grid (France, Netherlands, Belgium, Norway, Denmark, Ireland). Flows either way: import (+) when GB pulls p...
- ITSDO / TSDF
- Initial Transmission System Demand Out-turn / Transmission System Demand Forecast. "Gross" transmission-system demand (includes those exclusions).
- Metered / transmission-connected
- Large generators wired to the transmission grid (big wind farms, nuclear, gas, biomass). Visible to the operator in real time; this is what Elexon FUELINST r...
- MID
- Market Index Data: the day-ahead/within-day wholesale reference price (£/MWh), from APX/N2EX. We use it as a context line next to the imbalance price.
- NESO
- National Energy System Operator (formerly National Grid ESO). Runs the system, publishes open data (data.nationalgrideso.com / neso.energy) and co-runs the C...
- NIV (Net Imbalance Volume)
- the system's signed net imbalance (MWh) for a settlement period. Positive = system short (more demand than contracted generation → NESO net-buys → price tend...
- PN (Physical Notification)
- a BM Unit's notified intended MW level for a half-hour. A near-real-time plan, submitted before gate closure - not a meter (it can diverge widely from actual...
- PS / NPSHYD
- Pumped Storage / Non-Pumped-Storage Hydro (run-of-river). Distinct Elexon fuel fields; "Hydro" in the UI usually means NPSHYD.
- PV Live
- Sheffield Solar's modelled live GB solar output (MW), since solar isn't metered by the operator.
- REMIT
- Regulation on Energy Market Integrity and Transparency: requires market participants to publish "inside information", including generation unavailability (pl...
- REPD
- Renewable Energy Planning Database (DESNZ): renewable sites with coordinates, capacity, technology and status. A primary source for the station map.
- Settlement period
- A 30-minute slot used for market settlement; 48 per day (numbered 1-48). Much UK energy data is reported per settlement period.