Energy Flexibility Glossary: Ireland and Great Britain

A company that combines flexibility from many sites or assets into one portfolio that meets a market's or operator's requirements, and offers it on their behalf. An independent aggregator is not the customer's electricity supplier: the site keeps its own supply contract.

Paid for being contracted and ready across a service window, whether or not you are instructed. Normally subject to testing, so it means ready and provably ready, not just signed up.

NESO's main real-time tool for keeping GB supply and demand matched. Participants offer to increase or decrease their generation or demand, and are paid for responding when NESO accepts.

The estimate of what a site or asset would have used if it had not been asked to flex, calculated from its historical meter data. Delivered flexibility is measured and settled as the difference between the baseline and what the meter records.

Equipment on the customer's side of the meter, such as on-site generation, batteries and loads, which serves the site first and reaches the grid only through the site's own connection.

A battery installation that charges from and discharges to the electricity system, either as a standalone grid-scale site or behind a customer's meter. In the EirGrid and SONI Grid Codes, a battery energy storage power station is classed as a Power Park Module.

The area a network operator draws around a specific network constraint; flexibility products are bought per zone. Also written Constraint Managed Zone. A shared industry term from the Flexible Power standard products, used by NGED, UK Power Networks and SSEN among others - not one operator's coinage.

Ireland's independent energy and water regulator. Set up under the Electricity Regulation Act 1999 and later named the Commission for Energy Regulation, it has been the CRU since 2 October 2017. With Northern Ireland's Utility Regulator it jointly regulates the all-island SEM through the SEM Committee.

A site changing how much electricity it takes from the grid, and when, in response to a signal such as a price or an operator's instruction. Explicit demand response is contracted, dispatched and paid for; implicit demand response is a site reacting to time-of-use prices on its own account.

Smaller generation, storage and flexible demand connected to the distribution network, close to where power is used: for example solar and wind farms, batteries, commercial EV fleet charging and industrial demand response. Ofgem uses DER for business-owned assets and Consumer Energy Resources (CER) for household ones such as EVs, heat pumps and rooftop solar.

NESO's demand-side service. Since April 2026 it has procured zonally as well as nationally, lowered its threshold to 0.1 MW, and paid for turning demand up as well as down.

The licensed owner-operator of the local electricity network, and who you contact about a connection. Great Britain has 14 distribution licence areas.

A programme set up by EirGrid and SONI in 2011 to run the all-island system securely with more renewable generation. Under it, DS3 System Services, the services other than energy needed to keep the system secure, such as fast frequency response and operating reserves, are bought from providers in Ireland and Northern Ireland at regulated tariffs. They are being replaced by the Future Arrangements for System Services (FASS), built around a Day-Ahead System Services Auction (DASSA).

A role rather than a company: actively managing the network and buying flexibility instead of building more of it. In Great Britain the DSO function sits inside each DNO business and is governed separately from it.

The all-island market unit for demand response: one or more Individual Demand Sites that EirGrid or SONI can instruct to cut net demand, by reducing load or running on-site generation. Under EirGrid's Grid Code a DSU needs at least 4 MW to register; sites under 10 MW can be aggregated, while a site of 10 MW or more must be its own DSU.

Charges for using the distribution and transmission networks. In Ireland the CRU sets them each year for a tariff year running 1 October to 30 September: DUoS recovers ESB Networks' allowed revenue and demand TUoS (D-TUoS) recovers EirGrid's. Both are charged to suppliers, who decide how to pass them on in customers' bills.

The transmission system operator (TSO) for Ireland. With SONI, the TSO for Northern Ireland, it runs SEMO, the market operator for the all-island SEM, and procures system services under DS3.

Administers the Balancing and Settlement Code, and since December 2025 has been the Market Facilitator for distributed flexibility.

Trade body for network operators across the UK and Ireland. Publishes the Standard Agreement for Flexibility Services.

The distribution system operator (DSO) for Ireland. It connects sites to the distribution network and sets each connection's MIC and MEC; every connection on its network has an MPRN. Its allowed revenue is recovered through DUoS.

The party that contracts with a network or system operator to deliver flexibility from one or more assets. ESB Networks defines it as the legal entity that contracts with it to provide flexibility with one or several Flexible Service Assets; it may be the customer itself or an aggregator.

The settlement region a supply point sits in, lettered _A to _P with no _I or _O. One per licence area and normally the same ground, but it is a settlement attribute carried on the meter point rather than a licensed boundary.

In Great Britain, 6.6 kV and 11 kV: the voltage of the feeders leaving a primary substation. 22 kV and above is EHV.

Holds a distribution licence that is not geographically restricted, and typically owns the last-mile network on a new estate or business park, connected into the host operator's network at a defined point of connection. Distributor IDs run from about 24 up.

One of the 14 geographic areas of Great Britain covered by a distribution licence. The 14 are held by six licence groups under five ultimate owners. The areas have not changed since 1990; every change since has been ownership.

Two limits in an Irish connection agreement. MIC is the maximum electricity demand the connection is designed to supply, stated in kVA, usually close to the kW figure. MEC is the most the customer may export onto the ESB Networks system.

Identifies a GB supply point. The 13-digit bottom row, the core, identifies the supply point; the 8-digit top row adds profile and loss data, making 21 digits in all. The distributor is the first two digits of the core - digits 9 and 10 of the 21.

The unique 11-digit number that identifies an electricity connection in Ireland. It always begins with 10, belongs to the premises, and does not change. The GB equivalent is the MPAN.

Publicly owned since 1 October 2024. Runs the national transmission-level system and buys national services, including the Demand Flexibility Service.

The GB energy regulator. Issues distribution licences and sets the price control.

The older name for the same 14 licence areas, from when one company both distributed and supplied electricity in each. The Utilities Act 2000 split distribution from supply in 2001. Still appears in legacy documents.

Steps sub-transmission voltage down to the HV distribution voltage, usually 33 kV to 11 kV. Most procured distribution constraints are defined at this level or the one above it.

The second electricity distribution price control under Ofgem's RIIO framework (Revenue = Incentives + Innovation + Outputs), running 1 April 2023 to 31 March 2028. It placed the DSO obligation on every distribution licensee and required the DSO function to be governed separately from the DNO function.

The next GB electricity distribution price control, following RIIO-ED2 from 1 April 2028.

The wholesale electricity market for the island of Ireland, covering Ireland and Northern Ireland. It first went live on 1 November 2007, and new market arrangements (I-SEM) came in on 1 October 2018. The CRU and the Utility Regulator regulate it jointly through the SEM Committee, and SEMO, a joint venture of EirGrid and SONI, operates it.

A business that sits between a customer and an energy supplier to help the customer buy energy, manage a switch, or get contract advice: for example an energy broker or a price comparison website. In October 2025 the UK government said it intends to appoint Ofgem as the TPI regulator, legislating when parliamentary time allows; Ofgem's TPI market review call for input ran from 4 June to 16 July 2026.

The direction of a flexibility action. In NESO's usage, turn-down means reducing consumption or increasing export, and turn-up means increasing consumption or reducing export. Since 9 April 2026 NESO's DFS has bought both.

Paid for energy actually delivered when instructed.

A portfolio of many small assets, such as batteries, EV chargers, heat pumps or flexible site loads, controlled together so that it can be offered to markets as if it were one larger plant.