Adding a battery to an existing solar installation counts as a change to the site's generation configuration. The DNO needs to know about it.
What determines the application route
The existing installation, the new battery inverter, and the combined behaviour all matter.
If the combined system stays within the G98 threshold, the addition can usually be notified as a G98 in its own right, provided the battery inverter is type-tested to G98.
If the combined system pushes past the G98 threshold, a G99 application (often via Fast Track SGI-2) applies. This is common on domestic hybrid systems where a battery inverter is added alongside an existing solar inverter.
If the site already had a G99, the battery addition may be a G99 variation or a fresh G99 depending on the DNO. We'll work out which applies once we see the existing installation details.
What we need
- Details of the existing system: inverter make/model, kW rating, when it was notified/approved, and (if available) the original G98 or G99 reference.
- Details of the new battery: battery inverter make/model, kW rating, battery capacity in kWh, and mode of operation.
- Whether you're introducing an export limitation scheme.
Common mistakes
- Notifying only the new battery inverter. The DNO needs to see the whole picture, not just the new equipment.
- Missing the original G98/G99 reference. Not fatal, but slows things down. We can help find it if you know the original installer.
- Assuming the site is 'already approved'. Approval was for the original configuration. Adding a battery is a change.