G99 is the UK industry rule set for connecting larger embedded generation to the distribution network. It replaced the older G59 standard. The formal name is Engineering Recommendation G99, from the Energy Networks Association (ENA).
If your solar, battery, or combined system is above G98 limits, or the DNO treats it as non-small-scale, the connection goes through G99.
When G99 applies
G99 typically applies when generation:
- Exceeds 16 A per phase nameplate current (above roughly 3.68 kW single-phase or 11 kW three-phase under G98 thresholds), or
- Does not qualify for notify-only treatment under G98, or
- Needs specific DNO consent before export or energisation.
Commercial rooftops, large domestic arrays, and some battery export setups often use G99. Your installer assesses the correct route.
What happens under G99
G99 is usually an application and approval process with your DNO, not a simple post-install notification.
Typical steps:
- Application with site details, equipment specs, and your MPAN.
- DNO review, which may include limits on export or extra protection settings.
- Commissioning and compliance evidence before or after energisation, depending on the DNO.
- Registration of the connection on the network.
Timelines vary by DNO and system size. Plan ahead for larger installs.
G99 vs G98 (short comparison)
| G98 | G99 | |
|---|---|---|
| Typical size | Small (up to 16 A per phase) | Larger or complex |
| DNO process | Notification after install | Application and approval |
| Lead time | Usually short | Can take weeks |
Many Fox ESS home systems fall under G98, but hybrid inverters with high export capacity or additional generation may need G99.
G99 and monitoring your system
G99 governs permission to connect and export on the network. It does not change how Fox Cloud reports data once the system is running.
Check My Solar shows live and historical Fox ESS data (PV, battery, grid) when your plant is linked and reporting. See grid import and export for what appears in the app.
FAQ
Do I need G99 for a 10 kW home solar system?
It depends on phase, inverter rating, and DNO rules. A 10 kW inverter on a three-phase supply may still fit G98 on each phase. A 10 kW single-phase system often needs G99. Your installer confirms.
Can I export before G99 approval?
No. Energising or exporting without DNO approval where G99 applies can breach connection conditions. Follow your installer’s and DNO’s process.
Does G99 affect SEG export payments?
SEG is a supplier tariff. You still need a compliant grid connection (G98 or G99) and suitable export metering to receive export payments.