Glossary – UK Grid News

Network companies and organisations

DNO (distribution network operator): A company licensed to own and run the electricity distribution network in one of the 14 licence areas in Great Britain, carrying power from the transmission network to homes and businesses. Six groups hold the 14 licences. See our organisations pages.
IDNO (independent distribution network operator): A company with a distribution licence but no fixed area. IDNOs build or adopt networks, usually for new developments, that connect to a DNO's network, and charge for their use.
ICP (independent connection provider): An accredited contractor that builds the contestable parts of a connection, which are then adopted by a DNO or IDNO.
NERS (National Electricity Registration Scheme): The accreditation scheme, run by Lloyd's Register, that ICPs need in order to design and build connection works for adoption.
TO (transmission owner): A company that owns the high-voltage transmission network: National Grid Electricity Transmission in England and Wales, SP Transmission in central and southern Scotland, and SSEN Transmission in the north of Scotland.
OFTO (offshore transmission owner): A company that owns the transmission link from an offshore wind farm to the shore, appointed through Ofgem's tender process.
NESO (National Energy System Operator): The publicly owned body that operates the GB electricity system, runs the transmission connections process and leads strategic planning of the energy system. It took over from National Grid ESO in October 2024.
Ofgem: The GB energy regulator. It licenses network companies, sets their price controls and decides on changes to industry codes and charging.
DESNZ: The Department for Energy Security and Net Zero, the UK government department responsible for energy policy.
ENA (Energy Networks Association): The industry body for the companies that run the electricity and gas networks in Great Britain and Ireland.
NIE Networks and SONI: In Northern Ireland, NIE Networks owns the transmission and distribution networks and runs distribution, while SONI operates the transmission system. The Utility Regulator regulates them.

Connections

Connections queue: The list of projects holding connection agreements, each with a connection date. It grew far larger than the system needs, which led to connections reform.
Gate 1 and Gate 2: The stages of NESO's reformed connections process. At Gate 2, projects that meet readiness criteria and fit strategic plans are given a firm connection date and queue position.
Contestable and non-contestable works: Contestable works can be done by an accredited ICP. Non-contestable works, such as the final connection to the existing network and reinforcement, must be done by the network company.
Reinforcement: Upgrading the existing network, for example a bigger transformer or new cable, so it can take extra load or generation.
Flexible (non-firm) connection: A connection whose import or export can be reduced when the network is constrained, often in return for connecting sooner or at lower cost.
Co-location: Two or more technologies, such as solar and battery storage, sharing one site and grid connection.
GSP (grid supply point): A substation where the transmission network feeds the distribution network.
MW, MVA and kV: Megawatts (MW) measure real power, the usual unit for project size. MVA measures apparent power, often used for connection and transformer capacity. Kilovolts (kV) give the voltage level: transmission in Great Britain runs at 400kV and 275kV, and 132kV in Scotland.

Network charging

DUoS (distribution use of system): Charges that recover the cost of the distribution networks, set by each DNO under common methodologies (the CDCM and EDCM).
TNUoS (transmission network use of system): Charges that recover the cost of the transmission network, set by NESO. They vary by location.
BSUoS (balancing services use of system): Charges that recover NESO's costs of balancing the system.
Access and Forward-looking Charges review: An Ofgem review that, from April 2023, reduced what customers pay towards distribution network reinforcement when they connect.
Industry codes: The detailed rules for using the networks, such as the CUSC (transmission connection and use), the DCUSA (distribution use) and the Grid Code. Changes are proposed as modifications and decided by Ofgem.

Price controls and regulation

RIIO: Revenue = Incentives + Innovation + Outputs: Ofgem's framework for network price controls. See price controls.
RIIO-ED2: The price control for the distribution networks, from 1 April 2023 to 31 March 2028.
RIIO-T3: The price control for the transmission networks, from 1 April 2026 to 31 March 2031.
RIIO-ED3: The next distribution price control, due to start in April 2028.
Draft and final determinations: Ofgem's proposed and final decisions on each company's allowed spending, outputs and returns for a price control.
Totex: Total expenditure, capital and operating together, which RIIO uses to set allowances.

System operation and markets

DSO (distribution system operator): The role distribution companies take on in actively managing their networks: forecasting, buying flexibility and sharing data, rather than only building capacity.
Flexibility: Changing when or how much power is used or generated in response to a signal, so the network or system needs less capacity. Network companies buy it through flexibility markets.
Balancing Mechanism: NESO's main tool for matching supply and demand in real time, by accepting offers to change output or demand.
Capacity Market: Auctions that pay providers to be available when the system is tight, held four years ahead (T-4) and one year ahead (T-1).
CfD (Contract for Difference): The government's main support scheme for low-carbon generation. Projects bid in allocation rounds for a fixed strike price.
Cap and floor: A revenue scheme, regulated by Ofgem, that limits a project's income to a range: topped up to the floor and returned above the cap. It is used for interconnectors and long-duration storage.
LDES (long-duration energy storage): Storage that can deliver power for many hours, such as pumped hydro. See long-duration storage.
BESS (battery energy storage system): A grid-scale battery. See battery storage.

Planning and policy

Clean Power 2030: The government's mission for clean sources to supply almost all of Great Britain's electricity by 2030, set out in an action plan in December 2024.
SSEP (Strategic Spatial Energy Plan): NESO's plan for where generation and storage should be built across Great Britain.
CSNP (Centralised Strategic Network Plan): NESO's plan for the transmission network needed to deliver the SSEP.
RESP (Regional Energy Strategic Plan): Regional plans, led by NESO, that set out energy needs in each area of Great Britain to guide distribution network investment.
HVDC (high-voltage direct current): Technology used for long-distance and subsea links, such as interconnectors and links between Scotland and England.
Interconnector: A cable linking the GB system to another country's.
DCO and section 37 consent: Planning routes for major grid projects. In England, major schemes such as new high-voltage overhead lines need a development consent order (DCO). In Scotland, overhead lines need consent under section 37 of the Electricity Act 1989.
Great British Energy: The publicly owned energy company set up by the government to invest in clean power. See Great British Energy.

For the key dates behind these terms, see the policy timeline.