# Energy Flexibility Glossary: Ireland and Great Britain

> Plain definitions of demand response and flexibility terms used in Ireland and Great Britain, with the differences between the two markets, sources and the date each was last checked.

Published by Triple Edge Energy. HTML version: https://tripleedge.energy/glossary/
Last updated: 2026-11-02

## Aggregator

Markets: IE, GB. Topic: Organisations.

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.

Why it matters: Pooling lets a site that is too small to bid alone reach a service's minimum size. In GB, since November 2024 a Balancing and Settlement Code change (P415) has let independent aggregators sell flexibility into the wholesale market, and the government's July 2026 Clean Flexibility Roadmap update flagged work on whether supply contract terms block non-domestic customers from working with aggregators.

In Ireland: In the all-island market the aggregator usually operates a [DSU](https://tripleedge.energy/glossary/#dsu), contracting with individual demand sites that keep a separate supplier.

Also: Independent aggregator, DSU aggregator

Sources: [NESO, On-Boarding Flexibility](https://www.neso.energy/industry-information/balancing-services/flex-onboarding); [DESNZ, Ofgem and NESO, Clean Flexibility Roadmap (July 2025)](https://assets.publishing.service.gov.uk/media/68874ddeb0e1dfe5b5f0e431/clean-flexibility-roadmap.pdf); [GOV.UK, Clean flexibility roadmap: July 2026 update](https://www.gov.uk/government/publications/clean-flexibility-roadmap/clean-flexibility-roadmap-july-2026-update-accessible-webpage); [EirGrid and SONI, TSO Demand Side White Paper (13 December 2024)](https://www.eirgrid.ie/sites/default/files/publications/EirGrid-and-SONI-TSO-Demand-Side%20White-Paper-December-2024.pdf)
Last checked: 2026-11-02. Link: https://tripleedge.energy/glossary/#aggregator

## Availability payment

Markets: All. Topic: Commercial and payments.

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.

Why it matters: The predictable part of flexibility revenue. Unlike a [utilisation payment](https://tripleedge.energy/glossary/#utilisation-payment), it does not depend on how often the operator calls.

Sources: [Flexible Power, standard flexibility products](https://www.flexiblepower.co.uk/)
Last checked: 2026-08-24. Link: https://tripleedge.energy/glossary/#availability-payment

## Balancing Mechanism

Markets: GB. Topic: Markets and services.

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.

Why it matters: Fast assets such as batteries are well suited to it. Independent aggregators can take part as Virtual Lead Parties, alongside suppliers.

In Ireland: In the all-island market, EirGrid and SONI issue dispatch instructions to demand-side units at an aggregate level, and the unit operator spreads the response across its sites. See [DSU](https://tripleedge.energy/glossary/#dsu).

Also: BM

Sources: [NESO, On-Boarding Flexibility](https://www.neso.energy/industry-information/balancing-services/flex-onboarding); [GOV.UK, Clean flexibility roadmap: July 2026 update](https://www.gov.uk/government/publications/clean-flexibility-roadmap/clean-flexibility-roadmap-july-2026-update-accessible-webpage); [EirGrid and SONI, TSO Demand Side White Paper (13 December 2024)](https://www.eirgrid.ie/sites/default/files/publications/EirGrid-and-SONI-TSO-Demand-Side%20White-Paper-December-2024.pdf)
Last checked: 2026-11-02. Link: https://tripleedge.energy/glossary/#balancing-mechanism

## Baseline

Markets: All. Topic: Metering and data.

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.

Why it matters: The baseline method decides what counts as delivery, and methods differ between services. ESB Networks' April 2026 Local Business Flex consultation proposed a rolling quarterly baseline from the previous 12 months' meter data, excluding event days; NESO's [DFS](https://tripleedge.energy/glossary/#dfs) offers non-domestic participants an optional self-nominated baseline.

Sources: [ESB Networks, Local Business Flex Product Proposal Consultation (April 2026)](https://www.esbnetworks.ie/docs/default-source/database-documents/local-business-flex-product-proposal-consultation.pdf); [NESO, On-Boarding Flexibility](https://www.neso.energy/industry-information/balancing-services/flex-onboarding)
Last checked: 2026-11-02. Link: https://tripleedge.energy/glossary/#baseline

## Behind the meter

Markets: All. Topic: Technology and assets.

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.

Why it matters: Behind-the-meter generation and storage can provide demand-side flexibility by changing what the site draws from the grid. Export is limited by the connection agreement; in Ireland, by the [MEC](https://tripleedge.energy/glossary/#mic-mec).

Also: BTM, On-site

Sources: [NESO, On-Boarding Flexibility](https://www.neso.energy/industry-information/balancing-services/flex-onboarding); [EirGrid and SONI, TSO Demand Side White Paper (13 December 2024)](https://www.eirgrid.ie/sites/default/files/publications/EirGrid-and-SONI-TSO-Demand-Side%20White-Paper-December-2024.pdf); [ESB Networks, Conditions Governing the Connection and Operation of Export Limiting Schemes at LV and MV](https://www.esbnetworks.ie/docs/default-source/publications/conditions-governing-connection-operation-els.pdf)
Last checked: 2026-11-02. Link: https://tripleedge.energy/glossary/#behind-the-meter

## BESS (Battery Energy Storage System)

Markets: All. Topic: Technology and assets.

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.

Why it matters: Behind the meter, a battery can provide demand response by raising site demand when charging and cutting what the site takes from the grid when discharging. UK grid-scale battery capacity reached 7.5 GW in 2025, according to DESNZ.

Also: Battery storage, Battery ESPS

Sources: [EirGrid and SONI, Battery ESPS Grid Code Implementation Note v3.0 (December 2021)](https://www.eirgrid.ie/sites/default/files/publications/Integration-of-Batteries-Implementation-Note.pdf); [EirGrid and SONI, TSO Demand Side White Paper (13 December 2024)](https://www.eirgrid.ie/sites/default/files/publications/EirGrid-and-SONI-TSO-Demand-Side%20White-Paper-December-2024.pdf); [GOV.UK, Clean flexibility roadmap: July 2026 update](https://www.gov.uk/government/publications/clean-flexibility-roadmap/clean-flexibility-roadmap-july-2026-update-accessible-webpage)
Last checked: 2026-11-02. Link: https://tripleedge.energy/glossary/#bess

## CMZ (Constraint Management Zone)

Markets: GB. Topic: Network and connection.

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.

Why it matters: A site only earns local flexibility revenue if it sits inside a zone that is being tendered. Sites cannot be combined across zones to reach a minimum size, because the product is locational.

Also: Constraint Managed Zone

Sources: [Flexible Power](https://www.flexiblepower.co.uk/)
Last checked: 2026-08-24. Link: https://tripleedge.energy/glossary/#cmz

## CRU (Commission for Regulation of Utilities)

Markets: IE. Topic: Organisations.

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](https://tripleedge.energy/glossary/#sem) through the SEM Committee.

Why it matters: The CRU approves ESB Networks' and EirGrid's allowed revenues and the network tariffs ([DUoS and TUoS](https://tripleedge.energy/glossary/#duos-tuos)) that suppliers pass through to business bills. The GB counterpart is [Ofgem](https://tripleedge.energy/glossary/#ofgem).

Formerly: Commission for Energy Regulation (CER), Commission for Electricity Regulation

Sources: [CRU, About us](https://www.cru.ie/about-us/); [CRU, Policy and Statutory Framework](https://www.cru.ie/about-us/what-we-do/policy-and-statutory-framework/); [Law Reform Commission, Electricity Regulation Act 1999, section 8 (revised, with change-of-name annotation)](https://revisedacts.lawreform.ie/eli/1999/act/23/section/8/revised/en/html); [SEM Committee, The SEM](https://www.semcommittee.com/sem); [CRU, CRU approves 2026/27 electricity network charges and reduced PSO Levy (29 July 2026)](https://www.cru.ie/about-us/news/cru-approves-202627-electricity-network-charges-and-reduced-pso-levy/)
Last checked: 2026-11-02. Link: https://tripleedge.energy/glossary/#cru

## Demand response

Markets: All. Topic: Markets and services.

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.

Why it matters: Response can come from reducing load, moving it to another time, or running on-site generation or storage, so taking part does not always mean shutting plant down.

Also: DSR, Demand side response, Demand-side flexibility

Sources: [EirGrid and SONI, TSO Demand Side White Paper (13 December 2024)](https://www.eirgrid.ie/sites/default/files/publications/EirGrid-and-SONI-TSO-Demand-Side%20White-Paper-December-2024.pdf); [NESO, On-Boarding Flexibility](https://www.neso.energy/industry-information/balancing-services/flex-onboarding); [ESB Networks, Flexible demand](https://www.esbnetworks.ie/services/optimise-my-energy-use/flexible-demand)
Last checked: 2026-11-02. Link: https://tripleedge.energy/glossary/#demand-response

## DER (Distributed Energy Resources)

Markets: All. Topic: Technology and assets.

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.

Why it matters: These are the assets that distribution-level flexibility markets are designed to reach.

Also: Distributed energy assets

Sources: [Ofgem, Flexibility Market Asset Registration: Decision (March 2025)](https://www.ofgem.gov.uk/sites/default/files/2025-03/Flexibility-Market-Asset-Registration-Decision.pdf)
Last checked: 2026-11-02. Link: https://tripleedge.energy/glossary/#der

## DFS (Demand Flexibility Service)

Markets: GB. Topic: Markets and services.

[NESO](https://tripleedge.energy/glossary/#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.

Why it matters: The 0.1 MW threshold brings smaller sites, or small groups of sites, within reach of a national service.

Sources: [NESO, Demand Flexibility Service](https://www.neso.energy/industry-information/balancing-services/demand-flexibility-service-dfs)
Last checked: 2026-11-02. Link: https://tripleedge.energy/glossary/#dfs

## DNO (Distribution Network Operator)

Markets: GB. Topic: Organisations.

The licensed owner-operator of the local electricity network, and who you contact about a connection. Great Britain has 14 distribution [licence areas](https://tripleedge.energy/glossary/#licence-area).

In Ireland: Ireland has one distribution system operator, ESB Networks, so there is one distribution counterparty rather than several.

Sources: [Energy Networks Association, Who's my network operator?](https://www.energynetworks.org/customers/find-my-network-operator); [NESO, GIS Boundaries for GB DNO Licence Areas](https://www.neso.energy/data-portal/gis-boundaries-gb-dno-license-areas)
Last checked: 2026-08-24. Link: https://tripleedge.energy/glossary/#dno

## DS3 (Delivering a Secure Sustainable Electricity System)

Markets: IE, NI. Topic: Markets and services.

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).

Why it matters: In June 2025 the SEM Committee extended the DS3 regulated arrangements until DASSA go-live or 30 September 2027, whichever comes first (SEM-25-031). In June 2026 EirGrid and SONI said a May 2027 go-live was not feasible, and at July 2026 a new date was not yet confirmed.

Also: DS3 System Services, FASS, DASSA

Sources: [EirGrid and SONI, DS3 Programme Overview (2011)](https://www.eirgrid.ie/sites/default/files/publications/DS3-Programme-Overview-2011.pdf); [EirGrid, DS3 Programme](https://www.eirgrid.ie/ds3-programme-delivering-secure-sustainable-electricity-system); [SEM Committee, Future Arrangements for System Services: The Gap Decision Paper (SEM-25-031, 23 June 2025)](https://www.semcommittee.com/node/4081); [EirGrid, Future Markets Industry Workshop Q&A (24 June 2026)](https://www.eirgrid.ie/sites/default/files/publications/June-Future-Markets-Industry-Workshop-Q%26A.pdf); [EirGrid, Future Markets Technical Liaison Group Q&A (July 2026)](https://www.eirgrid.ie/sites/default/files/publications/Q%26A-July-2026-FM-Technical-Liaison-Group.pdf)
Last checked: 2026-11-02. Link: https://tripleedge.energy/glossary/#ds3

## DSO (Distribution System Operator)

Markets: GB, IE. Topic: Organisations.

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](https://tripleedge.energy/glossary/#dno) business and is governed separately from it.

Why it matters: The DSO is the buyer of local flexibility. It decides which constraints are tendered, and when.

In Ireland: ESB Networks is the DSO for Ireland.

Sources: [Ofgem, Electricity distribution price control 2023 to 2028 (RIIO-ED2)](https://www.ofgem.gov.uk/energy-regulation/how-we-regulate/energy-network-price-controls/electricity-distribution-price-control-2023-2028-riio-ed2)
Last checked: 2026-08-24. Link: https://tripleedge.energy/glossary/#dso

## DSU (Demand Side Unit)

Markets: IE, NI. Topic: Markets and services.

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.

Why it matters: The DSU is usually run by a third-party aggregator that is not the sites' supplier, so each site keeps its own supply contract.

Also: Individual Demand Site, IDS

Sources: [EirGrid, Demand Side Units](https://www.eirgrid.ie/grid/grid-codes-and-compliance-overview/grid-code-compliance-testing/dsu-setup-and-testing); [EirGrid and SONI, TSO Demand Side White Paper (13 December 2024)](https://www.eirgrid.ie/sites/default/files/publications/EirGrid-and-SONI-TSO-Demand-Side%20White-Paper-December-2024.pdf)
Last checked: 2026-11-02. Link: https://tripleedge.energy/glossary/#dsu

## DUoS / TUoS (Distribution Use of System / Transmission Use of System)

Markets: IE, GB. Topic: Commercial and payments.

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.

Why it matters: In Ireland, a site that draws more than its [MIC](https://tripleedge.energy/glossary/#mic-mec) may incur an excess capacity charge. GB uses DUoS for distribution and TNUoS (Transmission Network Use of System) for transmission, plus BSUoS (Balancing Services Use of System) for the system operator's balancing costs.

Also: Network charges, D-TUoS, TNUoS

Sources: [CRU, Electricity Distribution Network Allowed Revenues 2025 / DUoS Tariffs 2024/2025](https://www.cru.ie/publications/28251/); [CRU, Electricity Transmission Network Allowed Revenues 2025 / D-TUoS Tariffs 2024/2025](https://www.cru.ie/publications/28256/); [CRU, CRU approves 2026/27 electricity network charges and reduced PSO Levy (29 July 2026)](https://www.cru.ie/about-us/news/cru-approves-202627-electricity-network-charges-and-reduced-pso-levy/); [ESB Networks, Increase/decrease my supply](https://www.esbnetworks.ie/existing-connections/increasing-decreasing-supply/changing-your-level-of-supply-); [Ofgem, Targeted Charging Review glossary](https://www.ofgem.gov.uk/sites/default/files/docs/2019/11/tcr_glossary_0.pdf)
Last checked: 2026-11-02. Link: https://tripleedge.energy/glossary/#duos-tuos

## EirGrid

Markets: IE. Topic: Organisations.

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](https://tripleedge.energy/glossary/#sem), and procures system services under [DS3](https://tripleedge.energy/glossary/#ds3).

Why it matters: EirGrid and SONI dispatch demand-side units, and EirGrid's revenue is recovered through [D-TUoS](https://tripleedge.energy/glossary/#duos-tuos) charges. The closest GB counterpart is [NESO](https://tripleedge.energy/glossary/#neso).

Sources: [EirGrid and SONI, Battery ESPS Grid Code Implementation Note v3.0 (December 2021)](https://www.eirgrid.ie/sites/default/files/publications/Integration-of-Batteries-Implementation-Note.pdf); [SEMO, About the Single Electricity Market](https://www.sem-o.com/about); [EirGrid and SONI, TSO Demand Side White Paper (13 December 2024)](https://www.eirgrid.ie/sites/default/files/publications/EirGrid-and-SONI-TSO-Demand-Side%20White-Paper-December-2024.pdf); [CRU, Electricity Transmission Network Allowed Revenues 2025 / D-TUoS Tariffs 2024/2025](https://www.cru.ie/publications/28256/)
Last checked: 2026-11-02. Link: https://tripleedge.energy/glossary/#eirgrid

## Elexon

Markets: GB. Topic: Organisations.

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

Sources: [Elexon, Market facilitator for distributed flexibility](https://www.elexon.co.uk/what-we-do/about-our-services/market-facilitator-for-distributed-flexibility/)
Last checked: 2026-08-24. Link: https://tripleedge.energy/glossary/#elexon

## ENA (Energy Networks Association)

Markets: GB, IE, NI. Topic: Organisations.

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

Sources: [Energy Networks Association, Open Networks](https://www.energynetworks.org/work/open-networks/)
Last checked: 2026-08-24. Link: https://tripleedge.energy/glossary/#ena

## ESB Networks

Markets: IE. Topic: Organisations.

The distribution system operator (DSO) for Ireland. It connects sites to the distribution network and sets each connection's [MIC and MEC](https://tripleedge.energy/glossary/#mic-mec); every connection on its network has an [MPRN](https://tripleedge.energy/glossary/#mprn). Its allowed revenue is recovered through [DUoS](https://tripleedge.energy/glossary/#duos-tuos).

Why it matters: Working with the CRU, ESB Networks develops local flexibility products for business customers, such as Local Business Flex, consulted on in April 2026. The GB counterparts are the [DNOs](https://tripleedge.energy/glossary/#dno) in each licence area.

Sources: [CRU, Electricity Distribution Network Allowed Revenues 2025 / DUoS Tariffs 2024/2025](https://www.cru.ie/publications/28251/); [ESB Networks, Increase/decrease my supply](https://www.esbnetworks.ie/existing-connections/increasing-decreasing-supply/changing-your-level-of-supply-); [ESB Networks, What is an MPRN?](https://www.esbnetworks.ie/customer-support/customer-support-queries/meter-reading/details/manage-my-meter/what-is-an-mprn); [ESB Networks, Local Business Flex Product Proposal Consultation (April 2026)](https://www.esbnetworks.ie/docs/default-source/database-documents/local-business-flex-product-proposal-consultation.pdf)
Last checked: 2026-11-02. Link: https://tripleedge.energy/glossary/#esb-networks

## FSP (Flexibility Service Provider)

Markets: IE, GB. Topic: Organisations.

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](https://tripleedge.energy/glossary/#aggregator).

Why it matters: The FSP carries the contract obligations: in ESB Networks' proposed Local Business Flex products, a minimum number of delivery days a week and performance measured against the [baseline](https://tripleedge.energy/glossary/#baseline). GB uses the same term; Ofgem's March 2025 asset registration decision treats the FSP as the party holding the contract with the consumer.

Also: Flexible Service Provider

Sources: [ESB Networks, Local Business Flex Product Proposal Consultation (April 2026)](https://www.esbnetworks.ie/docs/default-source/database-documents/local-business-flex-product-proposal-consultation.pdf); [ESB Networks, Flexible demand](https://www.esbnetworks.ie/services/optimise-my-energy-use/flexible-demand); [Ofgem, Flexibility Market Asset Registration: Decision (March 2025)](https://www.ofgem.gov.uk/sites/default/files/2025-03/Flexibility-Market-Asset-Registration-Decision.pdf)
Last checked: 2026-11-02. Link: https://tripleedge.energy/glossary/#fsp

## GSP group (Grid Supply Point group)

Markets: GB. Topic: Metering and data.

The settlement region a supply point sits in, lettered _A to _P with no _I or _O. One per [licence area](https://tripleedge.energy/glossary/#licence-area) and normally the same ground, but it is a settlement attribute carried on the meter point rather than a licensed boundary.

Sources: [Elexon, Market Domain Data](https://www.elexon.co.uk/bsc/data/market-domain-data/)
Last checked: 2026-08-24. Link: https://tripleedge.energy/glossary/#gsp-group

## HV (GB usage) (High voltage)

Markets: GB. Topic: Network and connection.

In Great Britain, 6.6 kV and 11 kV: the voltage of the feeders leaving a [primary substation](https://tripleedge.energy/glossary/#primary). 22 kV and above is EHV.

In Ireland: ESB Networks calls 10 kV and 20 kV MV and reserves HV for 38 kV and up, so a GB "HV feeder" is an Irish "MV feeder".

Also: HV

Sources: [Triple Edge Energy, GB distribution licence areas, flexibility markets and owners](https://tripleedge.energy/blog/gb-distribution-licence-areas-flexibility-markets-owners/)
Last checked: 2026-08-24. Link: https://tripleedge.energy/glossary/#hv-gb

## IDNO (Independent Distribution Network Operator)

Markets: GB. Topic: Organisations.

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.

Why it matters: Being on an IDNO network changes how you identify the host operator for flexibility, not whether the site can take part.

Sources: [Ofgem, List of all electricity licensees including suppliers](https://www.ofgem.gov.uk/data/list-all-electricity-licensees-including-suppliers)
Last checked: 2026-08-24. Link: https://tripleedge.energy/glossary/#idno

## Licence area

Markets: GB. Topic: Network and connection.

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.

Why it matters: For a flexibility provider the useful unit is the licence group, because each group tenders across all its areas as one market: one registration, one qualification, one calendar. Fourteen when you read a licence, six when you register, five when you read the news.

Sources: [NESO, GIS Boundaries for GB DNO Licence Areas](https://www.neso.energy/data-portal/gis-boundaries-gb-dno-license-areas); [Ofgem, List of all electricity licensees including suppliers](https://www.ofgem.gov.uk/data/list-all-electricity-licensees-including-suppliers)
Last checked: 2026-08-24. Link: https://tripleedge.energy/glossary/#licence-area

## MIC / MEC (Maximum Import Capacity / Maximum Export Capacity)

Markets: IE. Topic: Network and connection.

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.

Why it matters: A site that draws more than its MIC may incur an excess capacity charge. Exporting from on-site generation or a battery is capped by the MEC; ESB Networks' export limiting scheme standard covers sites whose installed generation is larger than their MEC.

Also: Maximum Import Capacity, Maximum Export Capacity

Sources: [ESB Networks, Increase/decrease my supply](https://www.esbnetworks.ie/existing-connections/increasing-decreasing-supply/changing-your-level-of-supply-); [ESB Networks, Understanding connection capacity](https://www.esbnetworks.ie/services/get-connected/understanding-connection-capacity); [ESB Networks, Conditions Governing the Connection and Operation of Export Limiting Schemes at LV and MV](https://www.esbnetworks.ie/docs/default-source/publications/conditions-governing-connection-operation-els.pdf)
Last checked: 2026-11-02. Link: https://tripleedge.energy/glossary/#mic-mec

## MPAN (Meter Point Administration Number)

Markets: GB. Topic: Metering and data.

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.

Why it matters: Eligibility is checked per meter point, so the MPAN on a bill is the first thing to look up. Its distributor digits tell you which network operator, and so which flexibility market, the site belongs to.

In Ireland: Ireland uses the MPRN.

Also: Supply number, S-number

Sources: [Energy Networks Association, Who's my network operator?](https://www.energynetworks.org/customers/find-my-network-operator)
Last checked: 2026-08-24. Link: https://tripleedge.energy/glossary/#mpan

## MPRN (Meter Point Reference Number)

Markets: IE. Topic: Metering and data.

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](https://tripleedge.energy/glossary/#mpan).

Why it matters: Flexibility contracts identify each asset by its MPRN: in ESB Networks' Local Business Flex proposal, each Flexible Service Asset is a single MPRN.

Sources: [ESB Networks, What is an MPRN?](https://www.esbnetworks.ie/customer-support/customer-support-queries/meter-reading/details/manage-my-meter/what-is-an-mprn); [ESB Networks, How do I find my MPRN number](https://www.esbnetworks.ie/services/manage-my-meter/how-to-find-my-mprn); [ESB Networks, Local Business Flex Product Proposal Consultation (April 2026)](https://www.esbnetworks.ie/docs/default-source/database-documents/local-business-flex-product-proposal-consultation.pdf)
Last checked: 2026-11-02. Link: https://tripleedge.energy/glossary/#mprn

## NESO (National Energy System Operator)

Markets: GB. Topic: Organisations.

Publicly owned since 1 October 2024. Runs the national transmission-level system and buys national services, including the [Demand Flexibility Service](https://tripleedge.energy/glossary/#dfs).

In Ireland: EirGrid is the transmission system operator in Ireland, and SONI in Northern Ireland.

Formerly: National Grid ESO

Sources: [Ofgem, Decision notice to establish the National Energy System Operator](https://www.ofgem.gov.uk/publications/decision-notice-establish-national-energy-system-operator-neso)
Last checked: 2026-08-24. Link: https://tripleedge.energy/glossary/#neso

## Ofgem (Office of Gas and Electricity Markets)

Markets: GB. Topic: Organisations.

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

Sources: [Ofgem, List of all electricity licensees including suppliers](https://www.ofgem.gov.uk/data/list-all-electricity-licensees-including-suppliers)
Last checked: 2026-08-24. Link: https://tripleedge.energy/glossary/#ofgem

## PES region (Public Electricity Supplier region)

Markets: GB. Topic: Network and connection.

The older name for the same 14 [licence areas](https://tripleedge.energy/glossary/#licence-area), 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.

Sources: [NESO, GIS Boundaries for GB DNO Licence Areas](https://www.neso.energy/data-portal/gis-boundaries-gb-dno-license-areas)
Last checked: 2026-08-24. Link: https://tripleedge.energy/glossary/#pes-region

## Primary substation

Markets: GB. Topic: Network and connection.

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.

Why it matters: It is the last point with continuous telemetry and the point below which the network runs radially, which is why it is the usual boundary for whether a site's flexibility helps a constraint.

Also: Primary

Sources: [Triple Edge Energy, GB distribution licence areas, flexibility markets and owners](https://tripleedge.energy/blog/gb-distribution-licence-areas-flexibility-markets-owners/)
Last checked: 2026-08-24. Link: https://tripleedge.energy/glossary/#primary

## RIIO-ED2

Markets: GB. Topic: Regulation and policy.

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.

Sources: [Ofgem, Electricity distribution price control 2023 to 2028 (RIIO-ED2)](https://www.ofgem.gov.uk/energy-regulation/how-we-regulate/energy-network-price-controls/electricity-distribution-price-control-2023-2028-riio-ed2)
Last checked: 2026-08-24. Link: https://tripleedge.energy/glossary/#riio-ed2

## RIIO-ED3

Markets: GB. Topic: Regulation and policy.

The next GB electricity distribution price control, following [RIIO-ED2](https://tripleedge.energy/glossary/#riio-ed2) from 1 April 2028.

Sources: [Ofgem, Electricity distribution price control 2023 to 2028 (RIIO-ED2)](https://www.ofgem.gov.uk/energy-regulation/how-we-regulate/energy-network-price-controls/electricity-distribution-price-control-2023-2028-riio-ed2)
Last checked: 2026-08-24. Link: https://tripleedge.energy/glossary/#riio-ed3

## SEM (Single Electricity Market)

Markets: IE, NI. Topic: Markets and services.

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](https://tripleedge.energy/glossary/#cru) and the Utility Regulator regulate it jointly through the SEM Committee, and SEMO, a joint venture of EirGrid and SONI, operates it.

Why it matters: Rules that affect demand-side participation, such as those for a [DSU](https://tripleedge.energy/glossary/#dsu), are decided at all-island level by the SEM Committee rather than separately in each jurisdiction.

Also: I-SEM, Integrated Single Electricity Market

Sources: [SEM Committee, The SEM](https://www.semcommittee.com/sem); [SEMO, About the Single Electricity Market](https://www.sem-o.com/about); [SEMO, Quick Guide to the Integrated Single Electricity Market](https://www.sem-o.com/sites/semo/files/documents/training/Quick-Guide-to-the-I-SEM.pdf)
Last checked: 2026-11-02. Link: https://tripleedge.energy/glossary/#sem

## TPI (Third Party Intermediary)

Markets: GB, NI. Topic: Regulation and policy.

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](https://tripleedge.energy/glossary/#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.

Why it matters: TPIs are often paid a commission that the supplier adds to the customer's bill and passes on; in GB, suppliers must be transparent about TPI costs on non-domestic contracts signed on or after 1 October 2024. The government expects TPIs to play a growing role in time-of-use contracts and demand flexibility services.

In Ireland: In Ireland, brokers and energy consultants play the same role. In Northern Ireland, the Utility Regulator's May 2026 position paper set out a licence condition requiring suppliers to publish third party costs on a customer's principal terms and on request.

Also: Energy broker, Broker, Third-Party Intermediary

Sources: [GOV.UK, Regulating third-party intermediaries (TPIs) in the retail energy market: government response (updated 23 October 2025)](https://www.gov.uk/government/consultations/regulating-third-party-intermediaries-tpis-in-the-retail-energy-market/outcome/regulating-third-party-intermediaries-tpis-in-the-retail-energy-market-government-response-accessible-webpage); [Ofgem, Third-Party Intermediaries market review: call for input (4 June 2026)](https://www.ofgem.gov.uk/sites/default/files/2026-06/Third-Party_Intermediaries_Market_Review_Call_for_Input.pdf); [Ofgem, Non-domestic market review: decision (April 2024)](https://www.ofgem.gov.uk/sites/default/files/2024-04/Non-domestic_market_review_decision.pdf); [Utility Regulator, Third Party Intermediaries in the Energy Market: Position Paper (May 2026)](https://www.uregni.gov.uk/files/uregni/documents/2026-05/Position%20Paper-%20Final_0.pdf)
Last checked: 2026-11-02. Link: https://tripleedge.energy/glossary/#tpi

## Turn-up / turn-down

Markets: GB, IE. Topic: Markets and services.

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](https://tripleedge.energy/glossary/#dfs) has bought both.

Why it matters: Turn-up lets sites with flexible load earn from using more power when there is surplus on the system, as well as from cutting back at peaks.

In Ireland: Conventions differ, so check each contract. EirGrid and SONI use "turn-up" for raising on-site generation to cut a [DSU](https://tripleedge.energy/glossary/#dsu)'s net demand, and a DSU dispatched to a positive MW level is reducing demand. ESB Networks calls reducing demand or injecting power "Upward Flexibility".

Also: Demand turn-up, Demand turn-down, DTU

Sources: [NESO, On-Boarding Flexibility](https://www.neso.energy/industry-information/balancing-services/flex-onboarding); [NESO, Demand Flexibility Service (DFS)](https://www.neso.energy/industry-information/balancing-services/demand-flexibility-service-dfs); [EirGrid and SONI, TSO Demand Side White Paper (13 December 2024)](https://www.eirgrid.ie/sites/default/files/publications/EirGrid-and-SONI-TSO-Demand-Side%20White-Paper-December-2024.pdf); [ESB Networks, Local Business Flex Product Proposal Consultation (April 2026)](https://www.esbnetworks.ie/docs/default-source/database-documents/local-business-flex-product-proposal-consultation.pdf)
Last checked: 2026-11-02. Link: https://tripleedge.energy/glossary/#turn-up-turn-down

## Utilisation payment

Markets: All. Topic: Commercial and payments.

Paid for energy actually delivered when instructed.

Why it matters: Unlike an [availability payment](https://tripleedge.energy/glossary/#availability-payment), it cannot be forecast reliably, because it depends on how often the operator calls.

Sources: [Flexible Power, standard flexibility products](https://www.flexiblepower.co.uk/)
Last checked: 2026-08-24. Link: https://tripleedge.energy/glossary/#utilisation-payment

## VPP (Virtual Power Plant)

Markets: All. Topic: Technology and assets.

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.

Why it matters: The GB government's July 2026 Clean Flexibility Roadmap update names virtual power plants among the business models that market-access reforms will be assessed against.

Sources: [GOV.UK, Clean flexibility roadmap: July 2026 update](https://www.gov.uk/government/publications/clean-flexibility-roadmap/clean-flexibility-roadmap-july-2026-update-accessible-webpage)
Last checked: 2026-11-02. Link: https://tripleedge.energy/glossary/#vpp