G98 vs G99: How to Choose the Right DNO Route in Two Minutes
If you install solar panels or battery storage in the UK, knowing whether a job falls under G98 or G99 is essential.
We often get asked the same question: Does this installation need a G98 notification or G99 approval?
The answer depends on the system’s electrical output, the equipment already installed at the property and whether the installation meets the relevant requirements.
As a general guide, G98 covers eligible small-scale installations with a maximum output of 3.68 kW per phase (16 A). G99 applies to installations that exceed this limit or do not meet the G98 requirements.
Let’s look at how to tell the difference and what to check before starting a job.
G98 vs G99: What’s the Difference?
| Requirement | G98 | G99 |
|---|---|---|
| Maximum output | Up to 3.68 kW per phase (16 A) | Above 3.68 kW per phase, or installations outside G98 eligibility |
| When to contact the DNO | Notify the DNO within 28 days of commissioning | Apply before installation and obtain the required approval |
| Prior approval | Generally not required for eligible installations at a single premises | Required before connecting the installation |
| Common paperwork | G98 notification, commonly Form B | G99 application, such as A1-2 (Fast Track), A1-1 or the applicable simplified application form |
| Typical projects | Smaller domestic solar installations | Larger domestic systems, solar with battery storage and commercial installations |
Important: These are general guidelines. The correct route depends on the equipment, its operating settings and the relevant DNO requirements. Always check the latest guidance before submitting an application.
Four Things to Check Before Choosing G98 or G99
Before quoting for a job or submitting an application, check these four things.
1. What equipment is already installed?
Don’t look at the new solar system in isolation.
Check whether the property already has solar panels, a battery, a heat pump or an EV charger capable of exporting electricity.
Existing generation equipment can affect the total output that the DNO needs to consider. The way different devices operate also matters, so check the existing installation rather than assuming every piece of equipment can simply be added together.
2. What’s the inverter’s AC output?
The size of the solar array isn’t the same as the system’s electrical output.
For example, a 4.5 kWp solar array connected to a 3.68 kW inverter may fall within G98 limits, provided the complete installation meets the relevant requirements.
Always check the inverter’s rated AC output and the system’s configuration before deciding which route to follow.
3. Is there a battery that can export electricity?
This is an important check, especially when adding battery storage to an existing solar installation.
A battery with its own AC inverter may increase the site’s potential export capacity. If the combined installation exceeds the G98 limit, or otherwise falls outside G98 eligibility, a G99 application may be needed.
For example, adding a 5 kW AC-coupled battery inverter to an existing 3.6 kW solar inverter could take the site’s potential output well above the G98 threshold.
Don’t assume an existing G98 notification automatically covers a new battery installation.
4. Is it a single property or a group of properties?
If you’re working on several properties close together, such as a housing development, the DNO may need to assess the installations together.
The requirements depend on the project and the local network, so don’t assume that every small installation can be notified separately under G98.
Check with the relevant DNO before proceeding.
Three Common Installation Examples
Here are three examples to show how the rules can apply to real jobs.
Example 1: A straightforward domestic solar installation
A three-bedroom semi-detached house has a 3.6 kW inverter, a single-phase supply and no battery storage.
If the installation is type-tested and meets all the G98 requirements, it can generally follow the G98 route.
The installer completes the installation, commissions the system and notifies the DNO within 28 days.
Example 2: Adding a battery to an existing solar system
A homeowner already has a 3.6 kW solar inverter installed under G98. Two years later, they decide to add a 5 kW AC-coupled battery system.
The new battery inverter could increase the property’s potential output to 8.6 kW on a single phase.
This would normally require a G99 application, subject to the equipment configuration and applicable requirements. The necessary approval must be obtained before the new equipment is connected.
Depending on the DNO’s requirements, the project may qualify for the G99 Fast Track process. An export limitation may also help where the network has limited capacity.
Example 3: A larger domestic solar installation
A detached house has an 8 kWp solar array and a 6 kW hybrid inverter on a single-phase supply.
In this case, G99 would generally be the appropriate route because the inverter output exceeds the G98 limit.
If the local network has limited capacity, the DNO may require an export limit. A G100-compliant export limitation scheme may help the application meet the DNO’s requirements.
For example, limiting export to 3.68 kW could be an option, but it does not guarantee approval. The DNO must assess and accept the proposed arrangement.
What Happens If You Choose the Wrong Route?
Choosing the wrong application route can lead to delays, extra work and problems for your customer.
If a G99 installation is treated as G98: Connecting the equipment without the required DNO approval can breach the applicable connection requirements. The DNO may require the installation to be disconnected or its operation to be restricted until the issue is resolved. It can also delay export arrangements and any related payments.
If a G98 installation is submitted as G99 unnecessarily: You may end up completing extra paperwork and waiting for an approval process that the installation did not need. This can delay the project and affect your installation schedule.
The best approach is to confirm the correct route before installation rather than trying to fix the paperwork afterwards
