The energy industry is a complex system with many terms and acronyms. We have compiled a glossary of some of these to explain some of the details you may encounter.

National Data Terms

Exchange Trading (EPEX)

A trade executed on an authorised venue (for UK power this is either N2EX, EPEX or ICE). Only standard products are available, trading is anonymised but all transactions are available to members of the exchange

System Frequency (FREQ)

System Frequency is defined as the number of alternating current cycles in Hertz per second during the running time of a System.

Loss of Load Probability (LoLP)

The probability of demand having to be interrupted for security of supply reasons by National Grid.

Indicated Margin (MELNGC)

The System Operator communicates a forecast of Indicated Margin in the system each half hour for the following day. Each Settlement period is calculated by the sum of the National Demand Forecast by the System Operator and Maximum Export Limits submitted for that period.

Market Index Data (MID)

MID is a reflection of the price of wholesale electricity in the UK in short-term markets, where data is obtained for each Index Data Providers (MIDPs).

National Demand Forecast (NDF)

The System Operator oversees creating the National Demand Forecast. Based on the historically metered generation output for Great Britain, the System Operator will calculate this forecast. Transmission losses are included however demand from station transformers, pumped storage units and interconnector flows are not. These forecasts are unrestricted and include historical customer demand management data. A National Demand Forecast can be compared with an Initial National Demand Out-Turn INDO.

National Demand Forecast Day (NDFD)

A section of the 2-14 day forecast produced on a daily basis by the System Operator, the National Demand Forecast Day is produced in the same way as the daily National Demand Forecast. A half hourly average MW value is published each day in the 2-14 day forecast to illustrate the peak half hour of each day.

National Demand Forecast Week (NDFW)

A section of the 2-52 week forecast created each Wednesday by the System Operator, the National Demand Forecast Week is produced in the same methodology as the daily National Demand Forecast and includes the half-hourly average MW for the peak half hour in the week.

Net Imbalance Volume (NIV)

Each settlement period contains the Net Imbalance Volume which is the sum of the system and energy balancing action from this period, once netted off to provide the energy imbalance of a system. This is included in the System Sell/Buy Price Information received at this time. Pre-Gate Closure actions reported in BSAD are included.

Over the Counter (OTC)

A bilateral trade between two counterparties backed by a GTMA, this allows for trading of non-standard products. Prices/volumes are not publicly available.

System Sell Price (SSP)

Is the price received per MWh for over producing against your contracted level.

As of 05-11-2015: SBP = SSP

Short Term Operating Reserve (STOR)

Short Term Operating Reserve is required during specific times in the day to ensure the grid remains in balance. The Transmission Company will usually identify and resource this STOR requirement ahead of time.

Short Run Marginal Cost (SRMC)

Electricity production/consumption costs, i.e. the level at which an asset can generate profit by either increasing generation or decreasing consumption.

Wind Generation Forecast (WINDFOR)

A forecast of generation for all wind generation  Modules. This daily forecast is provided  4 times a day (04:30, 10:30, 16:30, 22:30) and each forecast includes 49 values covering the period from 21:00 on the current day (D) to 21:00 D+2.

General Industry Terms


An organisation that brings together distribution connected energy customers together as a group with the objective of obtaining better prices for energy services

Distribution network

A network that transports electricity from the transmission grid to end consumers.


High voltage transmission lines that transport electricity from power stations to major distribution substations.

Grid Event

Unseasonably cold temperatures and low wind speeds mean the UK’s generation is struggling to match national demand. National Grid needs help!


Import refers to the act of taking electricity from National Grid

National Grid UK

The National Grid UK is the transmission system operator (TSO) in Great Britain.

Price Management

We enable generators to take advantage of power price volatility throughout the day. This does expose you to risk as prices can be lower or higher than expected. We work with you to create a hedging strategy to manage this based on your risk appetite. We work with wind, solar, hydro, Hydro, AD, Landfill Gas and Battery Storage of every kind to maximise asset value and provide you with all market options.

We enable generators to leverage network charge/credits such as Balancing Service Use of System (BSUoS) and Generation Distribution Use of System (GDUoS) by ensuring generators are exporting at times when these prices are at their highest. GDUoS is known in advance, but BSUoS is forecast and hence has an additional risk as prices can be lower or higher than expected.

We work with customers to identify their profile to meet objectives, whilst considering a customer’s risk appetite. Our experienced traders will then actively manage this profile.


An organisation that sells electricity to end consumers.

Tagged Acceptance Volume

The amount of associated Acceptance Volume, excluded from the System Price Stacks by De Minimis Tagging, Arbitrage Tagging, NIV Tagging and/or PAR Tagging is called the Tagged Acceptance Volume.

Virtual Power Plant (VPP)

A VPP is a pool of small-scale generators and businesses with flexible demand that are aggregated and dispatched in response to grid balancing or market price signals, simulating the energy profile of a traditional power plant.