G98 or G99? The Solar-plus-Battery Grid Application Decision Framework
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Get the grid application wrong and a finished solar-and-battery install can sit switched off for weeks, waiting on the DNO. G98 or G99 is the first decision on every project – and a battery quietly changes the answer. This framework shows installers how to choose correctly, before commissioning day.
What is the difference between a G98 and a G99 application?
G98 and G99 are the two Energy Networks Association (ENA) engineering recommendations that govern how a small generator connects to the local distribution network. The difference is the approval route. G98 is a connect-and-notify process: the installer commissions the system, then notifies the Distribution Network Operator (DNO) within 28 days (Energy Networks Association, 2025). G99 reverses that order – the DNO must assess and approve the connection before the system is energised.
The dividing line is capacity per phase. A single-phase installation up to 16 A per phase – about 3.68 kW – falls under G98; anything above it needs G99. On a three-phase supply the G98 ceiling rises to roughly 11 kW, because the 16 A limit is measured on each phase (SurgePV, 2026).
When does a solar-plus-battery system need G99 instead of G98?
A battery pushes a project into G99 territory only when it can export to the grid above the 3.68 kW per-phase limit. The panels alone rarely trip the threshold on a domestic roof – it is the battery's inverter, and how it is configured, that usually decides the route (Capture Energy, 2025).
A battery counts toward the limit only if it is set to export. A hybrid inverter that can discharge to the grid adds its output to the PV export on that phase. Hold the export behind a hard, locked limit at or below 3.68 kW per phase and the system can often stay on G98 – though this depends on the DNO accepting the arrangement (Capture Energy, 2025).
- Solar only, inverter at or below 3.68 kW: G98 – connect and notify.
- Solar plus battery, export capped at or below 3.68 kW per phase: Often still G98, provided the export limit is hard-set and the DNO accepts it.
- Solar plus battery exporting above 3.68 kW per phase: G99 – full approval before energising.
How do you decide which application a project needs?
Four checks settle the question before design sign-off:
- Count the phases: Establish whether the property has a single-phase or three-phase supply – it sets the capacity ceiling of 3.68 kW per phase.
- Add up the inverter output: Total the export rating of every inverter that can push power to the grid – PV and battery together – on each phase.
- Check the export setting: Confirm whether the battery is set to export or held behind a hard export limit; only exporting capacity counts toward the threshold.
- Match to the route: At or below 3.68 kW per phase with no islanding, G98 applies; above it, or with non-standard equipment, prepare a G99 application.
Getting these figures onto the DNO form is where projects stall. autarc's grid registration keeps the inverter ratings, single-line diagram and equipment data consistent between the quote and the DNO submission, which cuts the rejections that come from mismatched paperwork.
What is the G99 Fast Track, and which projects qualify?
G99 Fast Track is a streamlined Stage 1 route for standard small systems, so most domestic and light-commercial battery jobs never touch the full G99 process. It applies to single- or three-phase inverters exporting up to 50 kW that use standard, MCS-certified equipment on a network with no immediate capacity objection.
A project usually qualifies when it meets all of these conditions:
- Export up to 50 kW, single- or three-phase.
- Standard, MCS-certified equipment, inverters and batteries the DNO already recognises.
- No islanding: Fast Track is not available for batteries designed to run during a power cut.
- Spare network capacity: The DNO can still object where the local network is constrained.
The reward is speed. Under Fast Track the DNO responds within roughly 20 business days, and some operators move faster – SSEN, for example, aims to reply within 10 working days (SSEN, 2026; GridGuru, 2026).
How long does each route take, and what does it cost?
Timelines and fees track the three routes closely, so the choice of application also sets the customer's expectation for switch-on.
What happens if you get the application wrong?
An incorrect or missing application can leave a commissioned system that the DNO orders switched off until it is regularised. Connecting a G99-scale system without approval breaches the connection agreement, and a retrospective application is slower and more exposed to refusal than one filed in advance (SolarGridCheck, 2026).
The cost lands beyond the connection itself. Export payment schemes such as the Smart Export Guarantee require a valid DNO notification alongside the MCS certificate before a supplier will pay for exported power (MCS, 2026). A missing G98 or G99 record can stall that registration, so the customer generates but earns nothing.
Conclusion: The battery's export setting decides the route
For most domestic jobs the decision turns on one figure: how much the system can export per phase. Establish the supply's phases, total the exporting inverters and confirm the export limit before design sign-off. Get that right and the G98 or G99 choice – and the DNO timeline – falls into place.
autarc: one platform for solar design, documentation and grid registration
The G98/G99 decision is only as reliable as the data behind it – inverter ratings, the single-line diagram and the export configuration all have to line up on the form. autarc brings solar design, construction documentation and DNO applications into one workflow, so the figures an installer signs off in design carry straight through to the grid application. Book a free demo and an autarc team member will show you the platform live.
References
- Demystifying the DNO G99 Application & Fast Track Notification System – GridGuru, accessed 30 July 2026, gridguru.co.uk
- Engineering Recommendation G98 Issue 2 (2025) – Energy Networks Association, accessed 30 July 2026, dcode.org.uk
- G98 & G99 Applications for UK Solar & Batteries – Capture Energy, accessed 30 July 2026, capture.energy
- G98 vs G99: Complete UK Solar Grid Connection Guide 2026 – SurgePV, accessed 30 July 2026, surgepv.com
- G99 Application UK: Avoid Rejection – SolarGridCheck, accessed 30 July 2026, solargridcheck.co.uk
- G99 Fast Track Process – SSEN, accessed 30 July 2026, ssen.co.uk
- Notifying DNOs – MCS, accessed 30 July 2026, mcscertified.com