Securing DNO approval for connecting solar panels and domestic battery storage to the UK electrical grid involves meeting strict safety and capacity standards set by local Distribution Network Operators (DNOs). Whether you are installing a compact 3.68 kW array or an extensive hybrid solar and battery storage system, understanding the difference between ENA Engineering Recommendation G98 and G99 is essential..
In this guide, we break down what a DNO is, how the notification and permission process works, and how to avoid costly delays when connecting to the National Grid.
What is DNO Approval and Why Does It Matter?
A Distribution Network Operator (DNO) is the licensed company responsible for maintaining the physical cables, substations, and electrical infrastructure that bring electricity to your property. Unlike your energy supplier (such as Octopus Energy, British Gas, or E.ON Next), who bills you for consumption, your DNO manages grid capacity and network stability.
There are six major DNO licence holders operating regional networks across Great Britain:
- UK Power Networks (UKPN): London, South East, and East of England
- National Grid Electricity Distribution (formerly Western Power): Midlands, South Wales, and South West
- SP Energy Networks: Central & Southern Scotland, Merseyside, and North Wales
- Scottish & Southern Electricity Networks (SSEN): Northern Scotland and Southern England
- Northern Powergrid: North East England and Yorkshire
- Electricity North West: North West England
Whenever you install a generation asset (such as solar PV) or energy storage that can feed electricity back into the grid, your DNO must be notified or give prior consent to prevent network overloading.
G98 vs G99: The Key Differences
The primary dividing line between application routes is the combined maximum inverter export capacity per phase.
| Feature | G98 (Connect & Notify) | G99 (Apply to Connect) |
|---|---|---|
| Max Capacity (Single Phase) | Up to 3.68 kW (16A per phase) | Greater than 3.68 kW |
| Max Capacity (Three Phase) | Up to 11.04 kW (16A per phase) | Greater than 11.04 kW |
| Prior Approval Needed? | No | Yes (written permission required) |
| Application Timeline | Within 28 days post-commissioning | 4 to 12 weeks before installation |
| Typical Cost | Free of charge | Usually free, unless network reinforcement is needed |
Understanding G98: “Connect and Notify”
If your combined inverter output does not exceed 3.68 kW on a single-phase domestic supply, your installation qualifies under G98.
How G98 Works:
- Your MCS-certified installer designs and fits the system.
- The system is fully commissioned and turned on immediately.
- Your installer submits the standard G98 commissioning notification form to your local DNO within 28 days of commissioning.
- The DNO logs the asset in their registry and issues a formal confirmation letter.
Note: Because 3.68 kW matches the standard 16 Amp single-phase ceiling, standard microgeneration setups (e.g., 8–10 panels with a 3.6 kW string inverter) almost always fall under G98.
When Does G99 Become Mandatory?
A G99 application is required if any of the following apply:
- Inverter Capacity Over 3.68 kW: You install an inverter rated at 5 kW, 6 kW, or 8 kW.
- AC-Coupled Battery Storage: If you have an existing 3.68 kW solar inverter and subsequently add an AC-coupled battery with its own 3 kW inverter, the total potential generation capacity becomes 6.68 kW.
- Export Limitation Failure: You install oversized hardware without certified export-limiting devices.
What is G99 “Fast Track”?
For many domestic systems between 3.68 kW and 7.36 kW that include an approved Export Limitation Scheme (ELS) adhering to ENA standards, DNOs offer a streamlined fast-track assessment (often called G99 Fast Track A1-1 or Fast Track A2). This reduces the waiting period from months to roughly 10–20 working days.
How to Check Your Current Connection
Before proceeding with an oversized solar array or substantial battery pack, verify your current domestic connection:
- Check Your Main Service Fuse: Look inside your meter cabinet. Most UK properties feature a 60A, 80A, or 100A cutout fuse. A 60A fuse may require a free fuse upgrade from your DNO before high-power inverters can be cleared.
- Look for Looped Supplies: Some terraced and semi-detached properties share an incoming service cable with a neighbour (a “looped supply”). If you share a supply, the DNO must unloop the cable before approving high-capacity generation.
Summary Checklist for Homeowners
- Under 3.68 kW export: Install, turn on, and let your installer notify within 28 days under G98.
- Over 3.68 kW export: Require installer to submit G99 paperwork and wait for official DNO approval before commissioning.
- Keep Your Documentation: Retain your DNO approval letter and MCS certificate; your energy supplier will require both before enrolling you into Smart Export Guarantee (SEG) export tariffs.
