Transmission Network Use of System (TNUoS)

Transmission Network Use of System (TNUoS)
Name	Transmission Network Use of System (TNUoS)
Country	United Kingdom
Introduced	1990s
Administered by	National Grid ESO
Tariff type	Fixed capacity and locational charging
Affected	Generators; suppliers; consumers

Transmission Network Use of System (TNUoS)

TNUoS is the principal locational charging regime for high-voltage transmission access in the United Kingdom, administered by National Grid ESO and implemented under licences and codes involving Office of Gas and Electricity Markets and statutes such as the Electricity Act 1989. It sets tariffs that recover transmission investment and running costs from parties connected to the National Electricity Transmission System and interfaces with market arrangements overseen by Department for Energy Security and Net Zero and regulated through mechanisms linked to Ofgem decisions and Energy Networks Association consultations. Its operation intersects with policy instruments and events such as the Wholesale Electricity Market reforms, the Great Britain Balancing Mechanism, and capacity arrangements coordinated with ENTSO-E standards.

Overview

TNUoS allocates charges to users of the high-voltage transmission grid, distinguishing locational signals across the England and Wales, Scotland, and Northern Ireland networks with settlement and invoicing administered by Elexon and system planning inputs from National Grid ESO and Scottish Power transmission owners. The framework evolved alongside privatisation milestones involving British Electricity Authority, Central Electricity Generating Board, and later structural changes influenced by the New Electricity Trading Arrangements and market events such as the Winter of Discontent (historical regulatory context). It is embedded in industry codes including the Connection and Use of System Code and the Balancing and Settlement Code.

Purpose and Legal Framework

TNUoS aims to allocate transmission network costs in a manner consistent with statutory duties under the Electricity Act 1989 and licence obligations of transmission owners such as National Grid Electricity Transmission and SP Energy Networks. Regulators like Ofgem set price controls (e.g., RIIO-2) and implement direction under ministers in Department for Business and Trade or Department for Energy Security and Net Zero policy statements. Legal challenges and judicial reviews have referenced tribunals such as the Competition Appeal Tribunal and judgments under the Administrative Law corpus, while industry stakeholders including RenewableUK, Energy UK, and Citizens Advice engage in consultations.

Charging Methodology

TNUoS charges combine locational tariffs derived from transmission investment models with fixed entry/exit components governed by methodologies produced by National Grid ESO and approved by Ofgem. The calculation uses loadflow and reinforcement cost allocations similar to methodologies discussed by European Network of Transmission System Operators for Electricity and parallels in frameworks such as the Nord Pool arrangements. Charges are applied under periods determined by settlement bodies like Elexon and involve treasury and regulatory oversight similar to interactions between Public Accounts Committee reviews and industry code governance by Energy Networks Association.

Impact on Generators and Consumers

TNUoS signals influence generator siting decisions for entities such as ScottishPower, SSE plc, RWE, EDF Energy, Centrica, Iberdrola, Statkraft, Ørsted, E.ON, Engie, Vistra Energy, Drax Group, SSE Renewables, Duke Energy, and merchant developers financing projects with lenders like European Investment Bank or investors such as BlackRock. For suppliers and large consumers including Tesco, British Steel, Tata Steel, Rolls-Royce, and Siemens, TNUoS affects wholesale pass-through, procurement strategies, and location-linked costs, interacting with contracts traded on venues like ICE and EPEX SPOT. Distribution network operators such as UK Power Networks and Western Power Distribution coordinate where relevant.

Calculation and Tariff Components

Tariffs comprise locational demand and generation residuals, capacity-related charges, and cost allocation elements determined from models of marginal reinforcement costs and long-run incremental cost studies managed by National Grid ESO engineers and approved through Ofgem consultation processes. Inputs draw on data sources and models used by bodies such as Carbon Trust, Committee on Climate Change, and academic groups at institutions like Imperial College London, University of Oxford, and University of Cambridge's energy research centres. Settlement uses metering rules aligned with Elexon and auditing standards akin to those applied by National Audit Office.

Criticisms and Reforms

Critiques by stakeholders including RenewableUK, Energy UK, Citizens Advice, and Members of Parliament across parties such as Conservative Party (UK), Labour Party (UK), and Scottish National Party cite distortions in siting incentives, cross-subsidisation between regions, and impacts on Scottish renewable projects versus English demand centres. Reforms considered in Ofgem determinations and policy white papers echo proposals from think tanks like the Institute for Public Policy Research, Policy Exchange, and Green Alliance and regulatory reviews including RIIO processes. Legal challenges and appeals have involved courts such as the High Court of Justice and UK administrative review mechanisms.

Case Studies and Historical Changes

Historical changes include tariff reforms following privatisation milestones and market redesigns tied to episodes like the Dash for Gas, the rise of offshore wind projects by developers such as Ørsted and ScottishPower Renewables, and the adaptation to low-carbon policy drivers from the Climate Change Act 2008. Notable case studies cover the effect on major projects: Beatrice Wind Farm, Hornsea Project, Dogger Bank Wind Farm, Whitelee Wind Farm, and terrestrial reinforcement investments like the Western HVDC Link and Celtic Interconnector planning interactions. Policy shifts after reviews by Ofgem and government initiatives such as regional network reinforcement and locational charging alternatives illustrate the evolving interaction among transmission owners, market participants, and policymakers.

Category:Electric power transmission in the United Kingdom