G98 or G99? The Solar-plus-Battery Grid Application Decision Framework
🔍 The key points at a glance
- G98 is a connect-and-notify route; G99 needs the DNO’s approval before the system energises.
- A battery only counts toward the 3.68 kW limit when it is set to export.
- A three-step check – phase, inverter rating, export setting – decides which application a project needs.
- G99 Fast Track clears standard sub-50 kW systems in about 20 business days.
- G98 notifications are usually free; full G99 assessments carry fees that vary by DNO.
- Skipping or misjudging the application risks disconnection and invalidated SEG payments.
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. 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 energises.
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 (SurgePV, 2026).
| G98 | G99 | |
|---|---|---|
| Route | Connect, then notify | Apply, then await approval |
| Single-phase limit | Up to 3.68 kW (16 A/phase) | Above 3.68 kW |
| Three-phase limit | Up to ~11 kW | Above ~11 kW |
| Approval timing | Within 28 days of commissioning | Before the system energises |
| Typical fee | Usually free | Depends on route and DNO |
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. A battery counts toward the limit only if it is set to export (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?
- Count the phases: Establish whether the property has a single-phase or three-phase supply.
- 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.
- Match to the route: At or below 3.68 kW per phase with no islanding, G98 applies; above it, prepare a G99 application.
What is the G99 Fast Track, and which projects qualify?
G99 Fast Track is a streamlined Stage 1 route for standard small systems. 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. Under Fast Track the DNO responds within roughly 20 business days (SSEN, 2026).
How long does each route take, and what does it cost?
| G98 | G99 Fast Track | G99 (full) | |
|---|---|---|---|
| Approval to energise | Not required | Required | Required |
| Typical DNO response | Notify within 28 days after commissioning | ~20 business days | Up to 45 working days |
| Best-fit system | ≤3.68 kW single-phase | Standard export ≤50 kW | Larger or non-standard |
| Typical fee | Usually free | Often free | Varies by DNO |
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. 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).
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.
autarc: one platform for solar design, documentation and grid registration
autarc brings solar design, construction documentation and DNO applications into one workflow. Book a free demo and an autarc team member will show you the platform live.
💬 FAQs
Do I need a DNO application for a battery-only installation with no solar?
Yes, if the battery can export to the grid. A storage system that charges from the grid and discharges back to it is treated as generation, so the same 3.68 kW per-phase threshold and G98/G99 split apply.
What is G100 and how does export limitation work?
G100 is the ENA framework for export limitation. It lets a system with a larger inverter cap its actual export to a set value – for example, holding a battery to 3.68 kW per phase so the project can stay on G98.
Can the system be installed before the G99 approval comes through?
No, under G99 the DNO must approve the connection before the system is energised. The equipment can be fitted, but it cannot be commissioned and switched on until approval is granted.
Who is responsible for the DNO application – the installer or the customer?
In practice the installer almost always handles it. The application needs technical detail – inverter data, a single-line diagram, MCS information – that only the installer holds.
Is DNO approval the same as planning permission?
No, they are separate consents. DNO approval covers the electrical connection to the grid; planning permission, or permitted development, covers the physical installation on the building.
Does MCS certification affect the grid application?
Yes, indirectly. Fast Track and the simpler routes assume standard, MCS-certified equipment, and export schemes such as the Smart Export Guarantee require both a valid DNO notification and an MCS certificate.
References
- G98 & G99 Applications for UK Solar & Batteries – Capture Energy, accessed 30 July 2026, https://www.capture.energy/blog/g98-and-g99-applications-for-solar-and-battery-storage
- G98 vs G99: Complete UK Solar Grid Connection Guide 2026 – SurgePV, accessed 30 July 2026, https://www.surgepv.com/solar-compliance/uk/guides/g98-vs-g99
- G99 Fast Track Process – SSEN, accessed 30 July 2026, https://www.ssen.co.uk/our-services/new-supplies/generation-connections/micro-generation-connections/g99-fast-track-process/
- Notifying DNOs – MCS, accessed 30 July 2026, https://mcscertified.com/installers/help-resources/notifying-dnos/