Enduring Auction Capability (EAC) | National Energy System Operator
Summary
NESO publishes detailed guidance for its Enduring Auction Capability (EAC) platform, which conducts co-optimised day-ahead procurement for frequency response and reserve services. The platform uses N-SIDE's algorithm to clear Dynamic Response, Quick Reserve, and Balancing Reserve services together at 14:00 daily, with Slow Reserve to be added in March 2026. Results are published via data portal with monthly archiving for sell orders and annual archiving for other datasets.
Why it matters
The EAC represents a shift from bilateral contracting to transparent auction-based procurement for ancillary services, allowing price discovery and co-optimisation across multiple balancing products. This creates clearer price signals for flexibility providers but concentrates procurement risk into daily auction windows rather than spreading it across longer-term contracts.
Key facts
- •Daily auctions at 14:00 for day-ahead delivery
- •Co-optimises Dynamic Response, Quick Reserve, and Balancing Reserve
- •Slow Reserve integration planned March 2026
- •Minimum 2-hour duration for flexible service windows
- •Results archived monthly (sell orders) and annually (other data)
Timeline
Areas affected
Related programmes
Memo
What this is about
NESO has launched its Enduring Auction Capability (EAC) platform, marking a fundamental shift from bilateral contracting to transparent auction-based procurement for ancillary services. The EAC uses N-SIDE's optimization algorithm to conduct co-optimised day-ahead auctions at 14:00 local time for Dynamic Response, Quick Reserve, and Balancing Reserve services, with Slow Reserve joining in March 2026.
This represents the clearest signal yet of NESO's commitment to market-based price discovery for balancing services. By co-optimising multiple products simultaneously, the platform allows providers to participate across services while NESO procures its requirements at least cost. The shift concentrates procurement risk into daily auction windows rather than spreading it across longer-term bilateral contracts, creating both opportunities and challenges for flexibility providers.
Key points
Platform mechanics: The EAC clears auctions daily at 14:00 using N-SIDE's power matching algorithm, which co-optimises across multiple balancing products to minimise total system cost. Providers submit sell orders specifying price, volume, and technical parameters, while NESO submits buy orders reflecting system requirements. The algorithm determines which orders clear and at what prices.
Service integration timeline: Dynamic Response and Quick Reserve launched first, with Balancing Reserve moving from its separate 08:15 auction to join the co-optimised 14:00 auction from October 29, 2025. The final morning Balancing Reserve auction runs October 28, after which all reserve procurement occurs at 14:00. Slow Reserve adds a third product layer from March 2026.
Flexible service windows: The January 2026 release introduces configurable service windows allowing providers to submit orders across consecutive 30-minute periods with minimum duration requirements (default 2 hours). This addresses the "crossover problem" at service window boundaries that previously created operational complexity.
Data transparency: Results publish via NESO's data portal with differentiated archiving schedules—sell orders archive monthly due to data volume while other datasets archive annually by financial year. The platform provides granular clearing data including marginal pricing, volumes cleared, and performance factors.
Overbidding prevention: New validation rules prevent battery units from submitting response service bids exceeding technical capability across multiple baskets. This addresses concerns about unrealistic bidding strategies that could distort price signals.
Locational procurement development: NESO is developing locational procurement capabilities for response and reserve services, recognising that system constraints increasingly drive requirements for services in specific network locations. This represents a significant evolution from the current national procurement model.
What happens next
Immediate implementation: Balancing Reserve completes its migration to the 14:00 co-optimised auction on October 29, 2025. The January 27, 2026 platform release enables flexible service windows functionality, though it only activates when Slow Reserve launches in March 2026.
Slow Reserve integration: March 2026 brings Slow Reserve into the co-optimised auction with three linked service windows covering morning (06:00-10:30), midday (10:30-15:00), and evening (15:00-21:00) periods. This reflects analysis of historical demand patterns and STOR availability.
Data architecture evolution: Annual archiving begins April 15, 2026, with pre-April 2026 data moving to financial year archives. Monthly archiving continues for sell orders due to file sizes. This improves data accessibility while maintaining historical transparency.
Locational procurement progression: Following November 2025 stakeholder engagement, NESO is developing detailed proposals for locational procurement of response and reserve services. This could fundamentally reshape how providers bid and how services clear, moving from national to constraint-driven procurement.
Platform expansion potential: The EAC architecture supports additional services and auction frequencies beyond the current day-ahead model. NESO has flagged potential for intraday auctions and new service types as the platform matures.
Market monitoring implications: The transparent auction format enables unprecedented visibility of balancing service costs and provider behaviour. Ofgem's market monitoring function will likely scrutinise clearing patterns for evidence of market power or coordination, particularly as the platform scales to include more services.
The EAC represents more than a procurement platform change—it signals NESO's strategic direction toward market-based solutions for system operation. Success depends on achieving sufficient competition across all service windows and locations to ensure robust price discovery while maintaining system security. The locational procurement development suggests NESO recognises that national markets may not adequately address increasingly complex network constraints.
For providers, the EAC creates opportunities for portfolio optimisation across multiple services but requires sophisticated bidding strategies and risk management as daily auction outcomes become less predictable than bilateral contract revenues. The platform's evolution toward locational procurement adds another layer of complexity that could advantage providers with geographically diverse portfolios.
Source text6,014 words
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Maybe later [Go to your account](/user/dashboard) # Enduring Auction Capability (EAC) The Enduring Auction Capability (EAC) is being designed to deliver co-optimised procurement for our day-ahead Frequency Response and Reserve products. It is envisioned that this method of procurement will allow us to meet our needs in the most efficient way, while enabling providers to participate in multiple markets. In the future, this procurement method could extend to new services and products. This may require different algorithms for auctions at various regularity, such as intra-day, day-ahead, and so on. We are eager to understand your views and so encourage you to [contact us](/cdn-cgi/l/email-protection#096b6671276f7c7d7c7b6c666f6b686568676a60676e7a6c7b7f606a6c7a497c622767687d60666768656c676c7b6e707a66276a6664) if you have any questions, feedback or would like to set up a meeting with the team. [Market information](#Market-information) [Locational procurement](#Locational-procurement) Market information Locational procurement Market information Please find below information on previous events we have held for the EAC, including webinar recordings and slides available to download. #### The EAC market design report This report provides a description of the EAC design and N-SIDE’s power matching algorithm. The purpose of this supporting document is to provide clarity and transparency on technical aspects of the EAC calculations, including the objective function of the algorithm, co-optimisation, the order format and associated functionalities, and the approach to determining clearing prices. [Download the market design report](/document/282401/download) #### Market design explainer We have published an explainer document, which gives an overview of some of the elements of the market design, and contains some simple examples of the construction of basic sell orders. [Download the market design explainer](/document/277671/download) #### Mock auction guidance document We have also published a mock auction guidance document, which gives an overview of how to register for the mock auctions, as well as the upcoming key dates. [Download the mock auction guidance document](/document/287581/download) #### EAC - Production environment access guidance document We have now published a guidance document for the production environment, this gives an overview of how to register for the production auctions, as well as gaining your API tokens. [Download the access guidance document](/document/289911/download) You can also download our [Q&A document](/document/274191/download) which will be regularly updated. Webinars/drop-in sessions Workshops Consultation drop-in sessions Legal Documents Training material EAC Releases Webinars/drop-in sessions Workshops Consultation drop-in sessions Legal Documents Training material EAC Releases ### EAC drop-in session - 09 December 2025 On 09 December 2025, we held a drop-in session to update industry on the proposed changes that are coming to the EAC UI changes in preparation for Slow Reserve. Below you can find the webinar recording and download the slides. | | | | --- | --- | | [Download slides](https://www.neso.energy/document/374211/download) | [Watch the webinar](https://players.brightcove.net/6415851838001/default_default/index.html?videoId=6386233842112) | ### ### EAC Webinar - 02 July 2025 On 02 July 2025, we held a webinar to update industry on the proposed changes that are coming to the EAC UI when Slow Reserve goes live. Below you can find the webinar recording. | | | --- | | [Watch the webinar](https://players.brightcove.net/6415851838001/default_default/index.html?videoId=6375201969112) | ### ### EAC webinar – 23 May 2023 On 23 May 2023, we held a webinar to update industry on the proposed sell-order design, a demo of the new UI, as well as project updates. Below you can find the relevant material shared during the webinar as well as an API quick start guide: | | | | | | --- | --- | --- | --- | | [Download slides](/document/280886/download) | [Watch the webinar](https://players.brightcove.net/867903724001/default_default/index.html?videoId=6328264835112) | [Download the Q&A](/document/280881/download) | [API Quick Start Guide](/document/280876/download) | ### Detailed Market Design – 17 February 2023 On 17 February 2023, we held the second webinar to update industry on the progress we have made on the Detailed Market Design of the EAC project. | | | | --- | --- | | [Download slides](/document/276866/download) | [Watch the webinar](https://players.brightcove.net/6415851838001/default_default/index.html?videoId=6351774102112) | ### Industry Webinar – 15 December 2022 On 15 December 2022, ESO held the first webinar to update industry on the progress we have made on the High-Level Market Design of the Enduring Auction Capability (EAC) project, including the feedback we have received from industry to date. | | | | --- | --- | | [Download slides](/document/273621/download) | [Watch the webinar](https://players.brightcove.net/6415851838001/default_default/index.html?videoId=6351775180112) | EAC results file for data portal As we proceed with development of the Enduring Auction Platform (EAC), we can now provide templates of the results files that market providers will be able to access post-auction via the data portal. [EAC results - sell orders](/document/286531/download) [EAC results format](/document/286536/download) [EAC results summary](/document/286541/download) [EAC results by unit](/document/286546/download) [EAC results - buy orders](/document/286551/download) Sell Order Design – 19 January 2023 As part of the SMP Show and Listen workshop on 19 January 2023, we presented the format of the sell order design for the EAC as part of our work for the Detailed Design phase of the project. [Download the EAC Sell Order Design](/document/275366/download) [Watch the EAC Sell Order Design presentation](https://players.brightcove.net/6415851838001/default_default/index.html?videoId=6351775180112) We recently held a number of consultation drop-in sessions, providing market participants with support following the release of Article 18 EBR consultation for the Enduring Auction Capability (EAC). Below you can find the session recordings alongside an example spreadsheet for calculation of settlement values that participants can use to visualise the changes to the settlement calculation, and see how much they would be paid (or pay ESO) for different clearing prices and performance factors. ### [EAC Roadmap - July 2023](/document/283721/download) [Consultation drop-in session - 05/07/23](https://players.brightcove.net/6415851838001/default_default/index.html?videoId=6351772536112) [Consultation drop-in session - 07/07/23](https://players.brightcove.net/6415851838001/default_default/index.html?videoId=6351774501112) [Consultation drop-in session - 12/07/23](https://players.brightcove.net/6415851838001/default_default/index.html?videoId=6351772922112) [Example spreadsheet for calculation of settlement value](/document/283281/download) ## Legal Documents | [Name](?order=title&sort=asc "sort by Name") | | --- | | [EAC - consultation changes summary](/document/290586/download) | | [EAC - mapping document](/document/290581/download) | | [EAC - response services service terms](/document/290576/download) | | [EAC - response services procurement rules](/document/290571/download) | | [EAC - new response services procurement rules](/document/290566/download) | | [EAC - proforma responses](/document/286016/download) | ## Archive | [Name](?order=title&sort=asc "sort by Name") | | --- | | [EAC - Summary of Changes Post Consultation](/document/286036/download) | | [EAC - New Response Services Service Terms Post Consultation](/document/286031/download) | | [EAC - New Response Services Procurement Rules Post Consultation](/document/286026/download) | | [EAC - Reserve/Response Procurement Rules (Combined EAC Procurement Rules) Post Consultation](/document/286021/download) | | Name | Published | | --- | --- | | [Add Basket With Children](https://players.brightcove.net/6415851838001/default_default/index.html?videoId=6351775165112) | 11 Jan 2023 | | [View results training video](https://players.brightcove.net/6415851838001/default_default/index.html?videoId=6351773626112) | 11 Jan 2023 | | [Add basket training video](https://players.brightcove.net/6415851838001/default_default/index.html?videoId=6351774310112) | 21 Sep 2023 | | [EAC Market Participant guide](/document/288801/download) | 21 Sep 2023 | ## EAC Results Annual Archiving — 15 April 2026 To improve data accessibility and usability, Results Summary, Buy Orders and Results by Unit will be archived annually by financial year, while Sell Orders will continue to be archived monthly due to data size. From 15 April 2026, all EAC data before 1 April 2026 will be removed from the four live datasets and moved to archives. Existing multi‑year archives will be split into one archive per financial year. Note: For clarity, all existing monthly archive datasets for Sell Orders will remain unchanged. Live datasets All data prior to 1 April 2026 will be removed from the following live datasets: * NESO Response-Reserve Results Summary * NESO Response-Reserve Buy Orders * NESO Response-Reserve Results By Unit * NESO Response-Reserve Sell Orders New archive datasets The removed data will be saved in the following archive files: * Results Summary / Buy Orders / Results by Unit (annual archives) + NESO Response-Reserve Results Summary FY2025 (Archive) + NESO Response-Reserve Buy Orders FY2025 (Archive) + NESO Response-Reserve Results By Unit FY2025 (Archive) * Sell Orders (monthly archives) + NESO Response‑Reserve Sell Orders 202504 (Archive) + NESO Response‑Reserve Sell Orders 202505 (Archive) + NESO Response‑Reserve Sell Orders 202506 (Archive) + NESO Response‑Reserve Sell Orders 202507 (Archive) + NESO Response‑Reserve Sell Orders 202508 (Archive) + NESO Response‑Reserve Sell Orders 202509 (Archive) + NESO Response‑Reserve Sell Orders 202510 (Archive) + NESO Response‑Reserve Sell Orders 202511 (Archive) + NESO Response‑Reserve Sell Orders 202512 (Archive) + NESO Response‑Reserve Sell Orders 202601 (Archive) + NESO Response‑Reserve Sell Orders 202602 (Archive) + NESO Response‑Reserve Sell Orders 202603 (Archive) Existing archive datasets The historical archive datasets for Results Summary, Buy Orders, and Results by Unit will be reorganised into one archive per financial year. The archived file names will be: * NESO Response-Reserve Results Summary FY2023-FY2024 (Archive) → NESO Response-Reserve Results Summary FY2023 (Archive) * NESO Response-Reserve Buy Orders FY2023-FY2024 (Archive) → NESO Response-Reserve Buy Orders FY2023 (Archive) * NESO Response-Reserve Results By Unit FY2023-FY2024 (Archive) → NESO Response-Reserve Results By Unit FY2023 (Archive) * NESO Response-Reserve Results Summary FY2024 (Archive) * NESO Response-Reserve Buy Orders FY2024 (Archive) * NESO Response-Reserve Results By Unit FY2024 (Archive) Going forward * Results Summary, Buy Orders and Results by Unit will be archived annually every April. Details of the process will be shared each March. * Sell Orders will be archived monthly, further details on the monthly archiving process will be shared in April. ## EAC Results Webpage Update — 3 March 2026 EAC Results Webpage Update — 3 March 2026 The existing archive file for EAC sell orders is very large, which can slow download speeds and make the data difficult to process. To improve data accessibility and usability, the NESO Response‑Reserve Sell Orders FY2023–FY2024 (Archive) dataset will be restructured into monthly files on Tuesday, 3 March. This change will make data access faster, more stable, and easier to use. The other three archived datasets and all four live datasets will remain unchanged. Updated Archive File Structure The archived file names will be: * NESO Response‑Reserve Sell Orders FY2023‑FY2024 (Archive) → NESO Response‑Reserve Sell Orders 202311 (Archive) * NESO Response‑Reserve Sell Orders 202312 (Archive) * NESO Response‑Reserve Sell Orders 202401 (Archive) * NESO Response‑Reserve Sell Orders 202402 (Archive) * NESO Response‑Reserve Sell Orders 202403 (Archive) * NESO Response‑Reserve Sell Orders 202404 (Archive) * NESO Response‑Reserve Sell Orders 202405 (Archive) * NESO Response‑Reserve Sell Orders 202406 (Archive) * NESO Response‑Reserve Sell Orders 202407 (Archive) * NESO Response‑Reserve Sell Orders 202408 (Archive) * NESO Response‑Reserve Sell Orders 202409 (Archive) * NESO Response‑Reserve Sell Orders 202410 (Archive) * NESO Response‑Reserve Sell Orders 202411 (Archive) * NESO Response‑Reserve Sell Orders 202412 (Archive) * NESO Response‑Reserve Sell Orders 202501 (Archive) * NESO Response‑Reserve Sell Orders 202502 (Archive) * NESO Response‑Reserve Sell Orders 202503 (Archive) Upcoming Activities EAC results for financial year 2025 will be archived in April 2026, with further details to be shared in March 2026. ## EAC Release - 27th Jan 2026 EAC Release (27th Jan 2026) There will be a new release of the EAC on 27th January 2026, this release will consist of the updates below: Slow Reserve. The new product will be visible in the UIs and APIs only at the business go-live date (currently planned for March 2025) Flexible Service Windows. The new feature will allow market participants to submit sell orders across multiple consecutive 30-minute periods, with a configurable minimum duration (default 2 hours), and the algorithm will ensure that the selected orders meet the minimum duration and have the same volume across the consecutive service windows. This new feature resulted in a redesign of the User Interfaces, as well as an introduction of new validation rules and constraints in the algorithm. The new User Interfaces will already be visible as of January 27th, but the new validation rules and algorithm modifications will be effective only at the business go-live of Slow Reserve when the feature will be activated (currently planned for March 2025). User Interface Enhancements. * The version of EAC is now displayed in the footer of the UI. * Added the possibility to delete all bids for all assets in a product/auction. API Enhancement. Improved handling of GraphQL errors and associated error messages. EAC Sandbox – linked windows update From 27th January 2026, we will be linking service windows in the sandbox for Slow Reserve. There will be three separately procured linked SR Window periods for each operational day during the transition period, as follows: Image  The three linked SR windows are supported by a detailed review of historical demand and STOR availability. These cover: * A morning window which will run from 06:00 to 10:30 * A midday window which will run from 10:30 to 15:00 * An evening window which will run from 15:00 to 21.00 Please revert to the [Transition Plan](https://www.neso.energy/document/370841/download "https://www.neso.energy/document/370841/download") and the [Slides](https://www.neso.energy/document/374926/download "https://www.neso.energy/document/374926/download") for more information on linked windows for Slow Reserve. ## EAC - Nov 2025 Release CIAM URL changes: The EAC production environment will be unavailable from 7:00 AM to 8:00 AM on 27th November 2025 as we implement CIAM URL updates. From 8:00 AM, the following CIAM endpoints will switch to: * OpenID Configuration <https://signin.neso.energy/as/.well-known/openid-configuration> * Authorisation Endpoint [https://signin.neso.energy/as/authorize](https://gbr01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fsignin.neso.energy%2Fas%2Fauthorize&data=05%7C02%7CSherry.Li%40neso.energy%7C44b1dd0779ed4d3d9b2a08de1b89c0ce%7Ca63c9e9eb4db442aa94f08718d788e8c%7C0%7C0%7C638978475651796774%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=xAsIcVb6H6tV0FigkHVh%2BGR1DACpFnd50Dl4Ob2D%2B58%3D&reserved=0) * Token Endpoint [https://signin.neso.energy/as/token](https://gbr01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fsignin.neso.energy%2Fas%2Ftoken&data=05%7C02%7CSherry.Li%40neso.energy%7C44b1dd0779ed4d3d9b2a08de1b89c0ce%7Ca63c9e9eb4db442aa94f08718d788e8c%7C0%7C0%7C638978475651814498%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=y90WK77yq4Os6icrbYgJDUCTn4gA%2BeelzK7COZsNSco%3D&reserved=0) * Token Introspection [https://signin.neso.energy/as/introspect](https://gbr01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fsignin.neso.energy%2Fas%2Fintrospect&data=05%7C02%7CSherry.Li%40neso.energy%7C44b1dd0779ed4d3d9b2a08de1b89c0ce%7Ca63c9e9eb4db442aa94f08718d788e8c%7C0%7C0%7C638978475651825582%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=uE1fylk%2Bo3yhAtPncrx4PLz9uywTNEoRUH002stYHxQ%3D&reserved=0) * Token Revocation [https://signin.neso.energy/as/revoke](https://gbr01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fsignin.neso.energy%2Fas%2Frevoke&data=05%7C02%7CSherry.Li%40neso.energy%7C44b1dd0779ed4d3d9b2a08de1b89c0ce%7Ca63c9e9eb4db442aa94f08718d788e8c%7C0%7C0%7C638978475651836784%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=%2BVVzDJxT7lSqM7EbLi7BbTjz1fSsJDMeiHgP%2Fz3h9fM%3D&reserved=0) * User Info Endpoint [https://signin.neso.energy/as/userinfo](https://gbr01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fsignin.neso.energy%2Fas%2Fuserinfo&data=05%7C02%7CSherry.Li%40neso.energy%7C44b1dd0779ed4d3d9b2a08de1b89c0ce%7Ca63c9e9eb4db442aa94f08718d788e8c%7C0%7C0%7C638978475651851221%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=B0GwNbUNM1GSTLVWc0%2FnURJrkCHi3RnWV8edE3Psf%2Fg%3D&reserved=0) * Signoff Endpoint [https://signin.neso.energy/as/signoff](https://gbr01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fsignin.neso.energy%2Fas%2Fsignoff&data=05%7C02%7CSherry.Li%40neso.energy%7C44b1dd0779ed4d3d9b2a08de1b89c0ce%7Ca63c9e9eb4db442aa94f08718d788e8c%7C0%7C0%7C638978475651866530%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=Ae%2BkA%2FQtLb4KhjoCvJ6hSqHsHO%2Bl%2Fw5U8BV7pRa%2BehA%3D&reserved=0) The EAC Production UI and EAC GraphQL API Endpoint will remain unchanged: * <https://eac.neso.production.n-side.com/marketparticipant> * <https://eac.neso.production.n-side.com/market-participant/api/graphql> This is a permanent change for the EAC production environment. Note: The CIAM URL has already been updated for the EAC sandbox environment since 9 October 2025. Please refer to previous release notes for more information. #### Industry drop-in session – 9th December We will be holding a drop-in session on Tuesday 9th December at 10:30am which will demo some UI changes we have made to the EAC platform in preparation for Slow Reserve in March 2026. To register your attendance to this session, [sign up here](https://events.teams.microsoft.com/event/7145cc21-e7c5-482b-8406-e16a2c0156c0%40a63c9e9e-b4db-442a-a94f-08718d788e8c) ## EAC Balancing Reserve Auction Update – 15 October 2025 The auction timing for Balancing Reserve will move from 08:15 to 14:00 local time (UK) to co-optimise with the day-ahead auctions for Dynamic Response services and Quick Reserve. * The final Balancing Reserve morning auction, "Balancing Reserve @ 08:15", will take place on Tuesday, 28 October at 08:15. After this date, all BR submissions will need to be entered into the afternoon auction. * The current co-optimised Dynamic Response and Quick Reserve auction, "Response & QR @ 14:00", will be renamed to "Response & Reserve @ 14:00" and will include the Balancing Reserve service. The renamed auction will appear as an upcoming auction from Wednesday, 15 October, with the first auction taking place on Wednesday, 29 October. After this date, providers will only see this auction on the EAC platform. * Auction results will be published [here](https://www.neso.energy/data-portal/eac-auction-results "https://www.neso.energy/data-portal/eac-auction-results") from Wednesday, 29 October. * For more information, please visit [here](https://www.neso.energy/industry-information/balancing-services/reserve-services/balancing-reserve). Note: The EAC sandbox environment will mirror production. In sandbox, the Balancing Reserve morning auction will expire on 28 October, and from 29 October onwards, there will be only one auction per day. ## EAC Sandbox Update (CIAM URLs Change) – 9 October 2025 The EAC sandbox environment will be unavailable from 10:00 AM to 2:00 PM on 9 October 2025 to implement CIAM URL updates. From 2:00 PM, the following CIAM endpoints will switch to: * OpenID Configuration [https://preprod.signin.neso.energy/as/.well-known/openid-configuration](https://preprod.signin.neso.energy/as/.well-known/openid-configuration "https://preprod.signin.neso.energy/as/.well-known/openid-configuration") * Authorisation Endpoint [https://preprod.signin.neso.energy/as/authorize](https://preprod.signin.neso.energy/as/authorize "https://preprod.signin.neso.energy/as/authorize") * Token Endpoint [https://preprod.signin.neso.energy/as/token](https://preprod.signin.neso.energy/as/token "https://preprod.signin.neso.energy/as/token") * Token Introspection [https://preprod.signin.neso.energy/as/introspect](https://preprod.signin.neso.energy/as/introspect "https://preprod.signin.neso.energy/as/introspect") * Token Revocation [https://preprod.signin.neso.energy/as/revoke](https://preprod.signin.neso.energy/as/revoke "https://preprod.signin.neso.energy/as/revoke") * User Info Endpoint [https://preprod.signin.neso.energy/as/userinfo](https://preprod.signin.neso.energy/as/userinfo "https://preprod.signin.neso.energy/as/userinfo") * Signoff Endpoint [https://preprod.signin.neso.energy/as/signoff](https://preprod.signin.neso.energy/as/signoff "https://preprod.signin.neso.energy/as/signoff") The EAC Sandbox UI and EAC GraphQL API Endpoint will remain unchanged: * [https://sandbox.eac.neso.production.n-side.com/marketparticipant](https://gbr01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fsandbox.eac.neso.production.n-side.com%2Fmarketparticipant&data=05%7C02%7CSherry.Li%40neso.energy%7Cae2083453fcb498d964e08de0660d197%7Ca63c9e9eb4db442aa94f08718d788e8c%7C0%7C0%7C638955210059518665%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=3Yq%2FfYbZS4CEDRq4g4itwIJIH%2BIZtbql2svDCNs%2FjtM%3D&reserved=0) * [https://sandbox.eac.neso.production.n-side.com/market-participant/api/graphql](https://gbr01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fsandbox.eac.neso.production.n-side.com%2Fmarket-participant%2Fapi%2Fgraphql&data=05%7C02%7CSherry.Li%40neso.energy%7Cae2083453fcb498d964e08de0660d197%7Ca63c9e9eb4db442aa94f08718d788e8c%7C0%7C0%7C638955210059538982%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=o7DIqSFl1kj0faCj71%2BGtYeQo88a2PqFYfg43nRxJhg%3D&reserved=0) This is a permanent change for the EAC sandbox environment. The production environment URLs remain unchanged. ## EAC Results Webpage Update 23 September 2025 Auction results for the 2PM Response and Reserve auctions will be archived on 23 September 2025, after publishing the daily auction results. Results for delivery dates on and after 1 April 2025 will remain in the current dataset. The resource IDs will remain unchanged, and the file names will be: * NESO Response-Reserve Results Summary * NESO Response-Reserve Buy Orders * NESO Response-Reserve Sell Orders * NESO Response-Reserve Results By Unit Results for delivery dates before 1 April 2025 will be archived. The archive file names will be: * NESO Response-Reserve Results Summary FY2023-FY2024 (Archive) * NESO Response-Reserve Buy Orders FY2023- FY2024 (Archive) * NESO Response-Reserve Sell Orders FY2023- FY2024 (Archive) * NESO Response-Reserve Results By Unit FY2023- FY2024 (Archive) Both live and archived datasets will be published [here](https://www.neso.energy/data-portal/eac-auction-results). Note: Auction results for the 8:15AM Balancing Reserve auction will remain unchanged, as the 8:15AM Balancing Reserve auction will move to the 2PM Response and Reserve auction soon. ## EAC Mock Auction Update 10 September 2025 The mock auctions will facilitate the transition of the Balancing Reserve from the 8:15 AM auction to the 2PM Response and Reserve auction. * Mock Auction Environment: The Mock Auction environment will be available to access from Wednesday 10th September. All data in Sandbox will be transferred to Mock Auction environment on Tuesday 9th September. + Auction URL: <https://mock-auction.eac.neso.production.n-side.com/marketparticipant> + API credentials: Credentials used in the sandbox environment can also be used in the mock auction environment. * Auction Dates: Mock Response and Reserve auctions, including 5 services (DC, DM, DR, BR, and QR), will be scheduled daily at 2PM from Monday 15th September to Sunday 21st September. * Auction Results: Mock auction results will be published [here](https://www.neso.energy/data-portal/eac-mock-auction-results). Results for auctions from 15th September to 19th September will be published on the same day. Results for auctions from 20th September to 21st September will be published on Monday 22nd September. * How to Participate:All participants in the sandbox will automatically have access to Mock Auction environment, and do not require additional registration. If you are already in the sandbox and wish to add any additional units or if you are not in the sandbox environment, please contact [[email protected]](/cdn-cgi/l/email-protection#04666b7c2a456a676d686865767d45777761777769616a70446a61776b2a616a6176637d) by the close of play on Tuesday 9th September. ## EAC Sandbox Update 19 August 2025 The EAC sandbox update scheduled for 19 August 2025 includes the following improvements: * Cloning Feature Fix: An issue with the cloning functionality in the Market Participant UI has been resolved. * Report API Enhancements: Two new fields, "consecutive" and "groupID", have been added to the report API. These fields are specifically applicable to Slow Reserve and do not apply to Response, Balancing Reserve, or Quick Reserve services. ## EAC Sandbox Update 11 August 2025 Starting from 11 August, Balancing Reserve will be added to the Response & Reserve @ 14:00 auction in the EAC sandbox environment. This update aims to facilitate the testing of a co-optimised auction of 5 services: DC, DM, DR, BR and QR. ## EAC Release 25 June 2025 The upcoming EAC Release on 25 June focuses on implementing a new validation rule to prevent overbidding and adding a new Linked Service Windows feature to prevent the crossover problems at service windows boundaries. The release includes: Prevent Overbidding * A new validation rule to prevent overbidding is applied to baskets associated with battery units providing Response services. Detailed information on this rule is available in the release documentation. * The sandbox environment will be updated with the overbidding feature from 20th June, we encourage providers to go in and test this ahead of the release in production on 25 June. Linked Service Window (LSW) * Introduction of the concept of Linked Service Windows to prevent the crossover problems at service windows boundaries. Initially, this feature will remain deactivated. NESO plans to provide advance notice to the market regarding the activation timeline. Market participants are encouraged to stay updated by following NESO communications for information on when this feature will become active. API Changes * Basket Composites feature added allowing providers to submit groups of baskets. * The API documentation has been expanded with new sections on Basket Composites and the Linked Service Windows feature. The Postman Collection has also been updated with examples of the new queries and mutations. * The API documentation ([Home](https://sandbox.eac.neso.production.n-side.com/docs/market-participant/api/home "https://sandbox.eac.neso.production.n-side.com/docs/market-participant/api/home")) will be updated after the release. ## EAC Release 4 Feb 2025 The upcoming EAC Release on 4th Feb includes significant improvements and fixes across multiple areas of the platform. This release focuses on enhancing API documentation. The improvements include: * API documentation: improve the section explaining how to retrieve the service windows, following a comment raised by a market participant and enhance section describing auction timings ## EAC Release 4 Dec 2024 The upcoming EAC Release on 4th Dec includes significant improvements and fixes across multiple areas of the platform. This release focuses on enhancing unit versioning capabilities, expanding order management functionalities, and improving overall platform accessibility. The improvements include: * Functionality to submit substitutable buy order families across: + Services with different service windows + Reserve and Response services * Fixed cloning functionality in Market Participant UI * Addressed maximum basket size limitation via API * Improved bookmark handling for CIAM-registered users * Added additional logging for invalid token usage * Fixed various UI display inconsistencies * Addressed order creation issues in the Operator UI Data Portal files Following our change from ESO to NESO, the EAC results files displayed on data portal will have their name changed. From Monday 25 November the files displayed will be named: * NESO Response-Reserve Results Summary 2023-2024 * NESO Response-Reserve Buy Orders 2023-2024 * NESO Response-Reserve Sell Orders 2023-2024 * NESO Response-Reserve Results By Unit 2023-2024 [EAC Auction Results](https://www.neso.energy/data-portal/eac-auction-results) AND * NESO Balancing-Reserve Results Summary 2023-2024 * NESO Balancing-Reserve Buy Orders 2023-2024 * NESO Balancing-Reserve Sell Orders 2023-2024 * NESO Balancing-Reserve Results By Unit 2023-2024 [EAC Auction Results](https://www.neso.energy/data-portal/eac-auction-results) Locational procurement Response & Reserve locational procurement webinar Response & Reserve locational procurement webinar ## Response & Reserve locational procurement webinar - 20 Nov On 20 November 2025 we shared our latest thinking on the Locational Procurement Service Design for Response and Reserve. [Download Slides](https://www.neso.energy/document/373051/download) [Download Q&A](https://www.neso.energy/document/373056/download) [Watch Webinar](https://players.brightcove.net/6415851838001/default_default/index.html?videoId=6385686697112) ## Response & Reserve locational procurement webinar - July 9 On July 9 we held a webinar to introduce our thinking on Locational procurement of Response and Reserve where we reviewed the key drivers and discussed early thinking on market design. [Download Slides](https://www.neso.energy/document/365031/download) [Download Q&A](https://www.neso.energy/document/365036/download) [Watch Webinar](https://players.brightcove.net/6415851838001/default_default/index.html?videoId=6375753010112) ## Stay Connected ### [Sign up for updates](https://neso.createsend.com/h/d/918820CF9659BD06) [](https://neso.createsend.com/h/d/918820CF9659BD06) Sign up to our newsletter and be the first to hear any news. ### [View our latest newsletter](https://neso.createsend.com/h/d/918820CF9659BD06) [](https://neso.createsend.com/h/d/918820CF9659BD06) Read our August 2024 update. ## Footer * [About NESO](/about-neso) + [Who we are](/about/our-people) + [Operational information](/about/operational-information) + [Careers](/careers) + [Applications, portals and APIs](/applications-portals-and-apis) * [Contact us](/contact-us) + [How to report a power cut](/energy-outages) + [Help centre](https://portal.nationalenergyso.com/nesoHelpCentre/s/) + [Media centre](/news-and-events/media-centre) * [Corporate information](/corporate-information) + [Suppliers](/suppliers) + [Freedom of Information and Environmental Information Regulations](/corporate-information/freedom-information-and-environmental-information-regulations) + [Modern Slavery Statement](/corporate-information/modern-slavery-statement) + [Public Sector Equality Duty (PSED)](/corporate-information/public-sector-equality-duty-psed) ## Site * [Accessibility](/accessibility) * [Privacy notice](/privacy-notice) * [Cookie policy](/cookie-policy) * [Terms and Conditions](/terms-and-conditions) * [Security](/security) * [Responsible Disclosure](/responsible-disclosure) ## Social * [Twitter](https://x.com/NESO_energy) * [LinkedIn](https://www.linkedin.com/company/neso-energy) * [YouTube](https://www.youtube.com/%40NESO_energy)  logo--facebook