GC0166 Q&A Workshop (1)
Summary
NESO's first Q&A workshop on GC0166 explains the MDO/MDB (Maximum Delivery Output/Bid) mechanism that replaces the 30-minute rule for battery dispatch in the Balancing Mechanism. Control points must submit minute-granularity energy availability data from real-time to 05:00 D+2, protecting volumes committed to frequency response and reserve contracts. Go-live is 22 June 2026, with transition running to November 2026 as individual control points certify readiness.
Why it matters
GC0166 is the most significant operational reform for battery storage since BM access. It replaces an arbitrary time-based assumption with actual state-of-energy data, which means NESO can finally dispatch storage assets based on what they can physically deliver rather than a crude 30-minute proxy. This is a structural improvement to dispatch accuracy that should reduce curtailment costs and improve battery utilisation — pricing capability rather than queuing it.
Key facts
- •MDO/MDB submissions at 1-minute granularity from current minute to 05:00 D+2
- •Go-live date: 22 June 2026, transition period to November 2026
- •Future State of Energy (FSoE) model uses real-time SoC via SCADA plus static parameters via Single Markets Platform refreshed every 30 minutes
- •Energy must be protected 4 settlement periods before and 2 after reserve/response contracts
- •Dynamic Containment requires 12.5 MWh protected per 50 MW contract (15-min delivery); Dynamic Moderation 25 MWh (30-min); Dynamic Regulation 50 MWh (60-min)
- •MDO/MDB can only be redeclared in BM gate for plant breakdown, post-BOA acceptance, PN changes, or exhausted ancillary service energy
- •Linked to Elexon P499, also going live 22 June 2026
- •BM system continues using 30-minute rule during transition; OBP uses mixture of MDO/MDB and 30-minute rule BMUs
Timeline
Areas affected
Related programmes
Memo
What this is about
GC0166 replaces the 30-minute rule — the crude assumption that every battery in the Balancing Mechanism can deliver for exactly 30 minutes — with actual state-of-energy data. From 22 June 2026, control points must submit Maximum Delivery Output (MDO) and Maximum Delivery Bid (MDB) values at minute-level granularity, telling NESO precisely how much energy a battery can deliver or absorb at any given moment. This is the operational infrastructure that makes accurate battery dispatch possible.
The first Q&A workshop walks through the mechanics: how MDO/MDB data flows, how operators must protect energy volumes committed to frequency response and reserve contracts, and how the transition works. It is detailed, operational, and aimed squarely at battery operators and their software suppliers who need to be ready by June.
Key points
MDO/MDB replaces a fiction with data. The 30-minute rule assumed uniform capability across all storage assets regardless of actual charge state, efficiency losses, or contractual commitments. MDO/MDB submissions run from the current minute through to 05:00 on D+2, at one-minute granularity, matching the Physical Notification submission horizon. NESO will finally know what a battery can actually do, not what a rule of thumb says it should be able to do.
Volume protection is the core complexity. Operators cannot simply declare their full state of energy as available. Energy committed to ancillary service contracts — Dynamic Containment, Dynamic Moderation, Dynamic Regulation, and reserve products — must be ring-fenced. The rules are specific:
- Reserve and response contracts: Protect energy in the 4 settlement periods before the delivery window (plus any additional trading time) and 2 settlement periods after. - Response contracts: Energy stays protected throughout the delivery window because response is delivered automatically as frequency deviates. The minimum volumes are prescribed: DC requires 12.5 MWh per 50 MW of contract (15 minutes continuous), DM requires 25 MWh (30 minutes), DR requires 50 MWh (60 minutes). - Reserve contracts: Energy is released back to NESO during the delivery window because reserve is instructed via Balancing Orders, not delivered automatically. This distinction matters — it means reserve-contracted batteries have more available volume for BM dispatch during their contract windows than response-contracted ones. - Physical Notifications: Protect 4 settlement periods before, but no protection needed after delivery, because the operator knows exactly when the PN will deliver.
The 4-SP protection window has a specific rationale. A Balancing Order could be accepted one minute before the BM gate moves. Once the gate moves, there is no opportunity to submit a new PN to recharge before the contract delivery period. Four settlement periods (two hours) is the minimum buffer to prevent a BOA from stranding the asset without enough energy to honour its commitments.
Redeclaration is tightly constrained. MDO/MDB values can only be changed within the BM gate window for: unavoidable events (breakdown or safety), after accepting a BOA, for PN changes in the settlement period after the BM window, or if ancillary service energy has been fully utilised. This is not a soft guideline — the conditions are codified in BC2.5.3.4.
The Future State of Energy (FSoE) model sits alongside MDO/MDB. NESO will use static data — daily cycle limits, MWh cycle limits, import/export power capability, charging and discharging efficiency — submitted via the Single Markets Platform, combined with real-time state of charge via SCADA, to model battery trajectories across the scheduling horizon. FSoE improves scheduling accuracy; MDO/MDB is the hard constraint that prevents any Balancing Order from exceeding actual capability by even a minute. The two systems are complementary, not substitutes.
Transition is per-control-point, not a single cutover. From 22 June to November 2026, NESO will run a mixed environment. Some control points will be submitting MDO/MDB; others will still operate under the 30-minute rule. The Optimal Balancing Platform will dispatch using whichever data each BMU provides. During transition, the BM system itself does not use MDO/MDB — it still assumes the 30-minute rule. The scheduling layer uses FSoE. This split means dispatch accuracy improves progressively as individual control points certify.
What happens next
- Now to June: Software suppliers test against BM EDL specification V8. Control points install EDL software and prepare MDO/MDB data generators. NESO publishes GC0166 Best Practice guidance. - 22 June 2026: Go-live. Elexon P499 (the corresponding BSC change) also goes live. ENCC business procedures updated. End-to-end training complete. - June to November 2026: Transition period. Control points individually agree go-live dates with NESO and begin submitting MDO/MDB data. No fixed deadline for individual cutover within this window, but the direction is clear. - FSoE trials: Running in parallel to validate exact data requirements. The model will not be 100% accurate — which is precisely why MDO/MDB exists as the hard constraint underneath it.
Battery operators who are not already engaged with their software suppliers on EDL V8 readiness have less than three months. The mechanism is well-designed — it prices capability rather than queuing it — but the implementation burden falls entirely on control points.
Source text
1 Public 1 Public GC0166 – Q&A Workshop 27/03/26 2 Public • Max SoE, ( NESO calculate time varying limits from Reserve and Response contracts) • Min SoE, • Charging efficiency • Discharging efficiency • SoE limit positive • SoE limit negative FSoE modelling will use data to allow NESO to schedule over the full PN submission time horizon in conjunction with other static data provided under GC166 (listed below) Once MDO/MDB is received we will start implementing the FSoE Model to increase the accuracy of the Scheduling process. As the FSoE model will not be 100% accurate the MDO/MDB data will ensure the actual BOA does not exceed the MWh capability by even a minute. The FSoE model will require a combination of the below data. The trials we are running will validate exact data requirements. All below is static , one value covering the operational day received via Single Markets Platform (SMP), apart from Real time SoE – which will be received via the SCADA system (IEMS). SMP values can be changed at any time and the system will refresh every 30 minutes. Future State of Energy (FSoE) model Implementation • Daily cycle limit • MWh cycle limit • MW power capability import • MW power capability export • MWh export • MWh import • Real time SoE SP 1 SP2 SP3 SP4 SP5 SP6 SP7 SP8 05:00 D+2 Real time SoC to 05:00 D+2 TimeNow MDO/MDB data submission horizon 3 Public Summary of Methodology • Main function of MDO/MDB to inform NESO about available MWh volume for BOA instruction (inside BM window) & scheduling (outside BM window) • MDO/MDB submissions made from the current minute onwards, with 1-min granularity, matching the time horizon for which PNs submitted (11:00 to 05:00 D+2) • MDO/MDB should be calculated ensuring any reserve/response contract volumes and PNs are protected SP 1 SP2 SP3 SP4 SP5 SP6 SP7 SP8 05:00 D+2 Real time SoC to 05:00 D+2 TimeNow MDO/MDB data submission horizon 4 Public GC0166 Transition Software Suppliers test against BM EDL Control Points inform NESO when ready EDL software installed MDO/MDB data generator ready GC0166 Best Practice Published EDL Specification V8 Published DVCD Rules V5 Published Control Points agree go-live date with NESO Elexon P499 Go-Live Control Points transition to send MDO/MDB E-2E Training for ENCC NESO Dispatch and Scheduling go-live Production files sent to Elexon ENCC Business Procedures Updated Complete testing with Elexon 22 June 2026 22 June 2026 22 June 2026 to November 2026 22 June 2026 5 Public Overview MDO/MDB or 30-minute rule Control Points BM System OBP BM EDL OBP EDL 30-minute rule Engineering Adjustment Battery BOAs (Path for BOAs depends on transition) Path depends on transition Data depends on control point readiness BM does not use MDO/MDB – still assumes 30-minute rule OBP FD TD, NDO using mixture of BMUs still on 30- minute rule and those on MDO/MDB Scheduling uses FSOE Battery Volume Calculator Path for BOAs depends on transition MDO/MDB or 30-minute rule Battery BOAs MDO/MDB or 30-minute rule Battery BOAs 6 Public 6 Public MDO/MDB 7 Public MDO/MDB MDO /MDB can be redeclared in the BM gate under the following conditions: • For unavoidable events (plant breakdown or safety grounds) • After a BOA is accepted • For a submitted PN change in the Settlement Period after the BM window • If the BMU has fully utilised energy reserved for delivery of ancillary services (Full details captured in BC2.5.3.4) 8 Public Protecting Energy Volume using MDO/MDB MDO/MDB must account for energy needed to deliver committed level and contracted ancillary services. In order to ensure these can be delivered, energy volumes must be protected. The two key scenarios where energy volume must be protected are: 1) For reserve & response contracts 2) For PNs 9 Public Protecting Energy Volume using MDO/MDB 1) For reserve & response contracts It is necessary to protect energy volume in the 4 SPs before the delivery window (+ any additional time needed for trading) and 2 SPs after. For response, volume remains protected during the delivery window, as it is delivered automatically, but for reserve, it is released back to be instructed by NESO (as per service design). 2) For PNs It is necessary to protect energy volume in the 4 SPs before the delivery window (+ any additional time needed for trading) only. As the provider knows exactly when the PN will deliver, the MDO/MDB can be submitted to reflect this. 10 Public Protect 4 SPs prior to reserve/response contract or PN Example: contract or PN starts at 12:30. In theory a BOA could be issued and accepted 1-min before the BM gate moves at 10:59. The BM gate moves at 11:00 and now covers 11:00 to 12:30 meaning no PN can be submitted before the contract or PN delivery SP and so no opportunity to adjust the asset SoC. Therefore the 10:30 to 11:00 SP should also be protected, and hence a minimum of 4 SPs protection is needed (10:30 to 12:30), plus any additional time required for trading. 11 Public Protect 2 SPs post reserve/response contract 12 Public No need to protect 2 SPs post PN 13 Public Response – minimum energy volumes to protect Response volume protected 4 SPs before contract delivery, 2 SPs after but also throughout as response is not instructed and is delivered automatically as frequency changes In this example, frequency was at 50Hz throughout and so no response volume was utilised. Dynamic Containment - Must be able to deliver continuously for 15 mins (for e.g. if DC contract is for 50MW, the unit must protect a minimum of 12.5MWh to be able to deliver response for 15 mins) Dynamic Moderation - Must be able to deliver continuously for 30 mins (for e.g. if DM contract is for 50MW, the unit must protect a minimum of 25MWh to be able to deliver response for 30 mins) Dynamic Regulation - Must be able to deliver continuously for 60 mins (for e.g. if DR contract is for 50MW, the unit must protect a minimum of 50MWh to be able to deliver response for 60 mins) 14 Public Use of MEL/MIL to protect frequency response 15 Public Reserve - energy volumes to protect and release Reserve volume protected 4 SPs before contract delivery, 2 SPs after but released during contract period as NESO need to instruct via BOAs, as designed In this example, PQR volume not utilised by NESO 16 Public PNs – fully charged 17 Public BOAs