G98 vs G99 in one paragraph
Both are Engineering Recommendations published by the Energy Networks Association. They tell DNOs how small generation and storage can connect to the low-voltage network without destabilising local voltage or protection. G98 covers the smaller end: inverters up to 16 A per phase. The process is a notification. G99 covers everything larger, including many 5 kW-plus hybrid inverters and stacked battery systems. The process is an application that the DNO must approve before energisation.
A G99 application is the formal request your installer sends to the DNO when the battery inverter exceeds the G98 size limit. It is not optional for those larger systems. Approval must come before the battery is allowed to export or operate in parallel with the grid.
When a home battery needs G99
The trigger is the inverter rating, not the battery kilowatt-hours. A 10 kWh pack with a 3 kW inverter can still sit under G98. A 5 kWh pack with a 5 kW inverter usually cannot.
- G98 territory: continuous AC output at or below 16 A per phase (roughly 3.68 kW on a normal single-phase domestic supply). Most compact all-in-one units aimed at overnight arbitrage are designed to sit here.
- G99 territory: anything above that continuous rating, three-phase systems in many cases, or sites where the DNO has already flagged local constraints.
If you already have solar with an existing G99 or G100 export limit, adding storage can interact with those settings. Your installer should check the existing agreement rather than assume a clean G98 path.
What the G99 application actually contains
Your installer prepares the pack. As a homeowner you rarely fill the form yourself. Typical contents include:
- Site address, MPAN and single-line diagram showing how the battery sits relative to the consumer unit and meter.
- Inverter make, model, continuous and peak ratings, and G99 type-test certificates.
- Protection settings (under/over voltage, frequency, loss-of-mains) and any export limitation scheme.
- Existing generation on site (solar, EV charger if relevant) so the DNO can assess aggregate impact.
The DNO reviews whether the local network can accept the connection without reinforcement. Most domestic battery applications are approved without physical works. A minority trigger a request for export limitation or, rarely, a contribution to network upgrades.
How long a G99 takes in 2026
There is no single national clock. DNOs publish their own service levels. A common target for a standard G99 application is around 45 working days from a complete submission. Incomplete forms, missing certificates or known network constraints push that out. Some regions are faster; some are slower when application volumes are high.
Compare that with G98. A G98 notification is often acknowledged within a few working days. The installer can usually schedule the fit once the notification is in, subject to the usual survey and wiring rules. That difference in calendar time is one practical reason many households choose a G98-class unit when 5 kWh is enough for their overnight-to-daytime shift on a tariff such as Octopus Go.
| G98 notification | G99 application | |
|---|---|---|
| Typical inverter limit (single-phase) | Up to ~3.68 kW continuous | Above ~3.68 kW |
| Process type | Notification | Application and approval |
| Typical DNO response | Days | Weeks (often ~45 working days target) |
| Can install before response? | Usually yes once notified | No. Wait for approval |
| Installer paperwork | Lighter | Full form, diagrams, certificates |
| Habo 5 kWh STREAM / Solarbank | Designed for this route | Not required for the standard unit |
Cost: what you actually pay
DNOs do not usually charge a separate application fee for a straightforward domestic G99. The cost sits in installer time: preparing the single-line diagram, collecting certificates, chasing the DNO if the file sits, and adjusting settings if the DNO asks for export limitation. Some quotes show that as a line item. Others fold it into the install price. Ask.
G98 is cheaper because the paperwork is lighter and the calendar risk is lower. That is part of why a fully installed 5 kWh G98-class system from £2,499 (0% VAT where that still applies in England, Scotland and Wales until 31 March 2027) can undercut larger G99 systems even before you compare the battery capacity you actually use each day.
Rule of thumb. If your evening and daytime base load is well covered by 5 kWh on a cheap overnight tariff, the G98 route keeps both the grid process and the install simple. If you need to shift 10 kWh or more every day, accept that G99 (or a larger G98 multi-unit arrangement) is part of the job and budget the time accordingly.
What happens if you ignore the process
Connecting a G99-scale inverter without approval is a breach of the distribution connection terms. DNOs can require disconnection. Insurers can take a dim view if a non-compliant system is involved in a claim. None of that is theoretical. The clean path is to let the installer run the correct process before the system is energised.
The same principle applies to location and wiring. Even a perfect G98 or G99 file does not override BS 7671 Amendment 4 and PAS 63100. Batteries still need a legal location (not a loft, bedroom or escape route) and a proper hardwired connection to the consumer unit.
How this fits Habo's offer
Habo sells a 5 kWh STREAM / Solarbank class all-in-one with the inverter in the box, electrician-wired under G98 / BS 7671, from £2,499 fully installed. Typical savings on a cheap overnight tariff such as Octopus Go are about £300 to £360 a year, one cycle a day, with payback around 7 to 8 years. No solar required. We are not taking deposits at the moment. Join the waitlist at /reserve with an email. Nothing to pay today. We get in touch when we can book the installation.
If your usage genuinely needs a larger inverter, a G99 application is the correct next step with a specialist installer. Do not try to force a bigger system through a G98 notification. The DNO process exists for a reason.
Frequently asked questions
G99 is the Engineering Recommendation that covers connecting larger generation and storage equipment to the UK distribution network. If your battery inverter is over 16 A per phase (about 3.68 kW on single-phase), your installer must submit a G99 application to your Distribution Network Operator (DNO) before install. Below that limit, a simpler G98 notification is usually enough.
Typical G99 timescales are measured in weeks, not days. Many DNOs aim to respond within 45 working days for a standard application, but complex sites, incomplete paperwork or local network constraints can stretch that. G98 notifications are far quicker, often acknowledged in days. Always ask your installer for the current lead time for your postcode.
Usually no. Habo's 5 kWh STREAM / Solarbank class all-in-one has the inverter in the box and is designed to stay under the 3.68 kW G98 threshold on a single-phase supply. That keeps the grid process as a notification rather than a full G99 application. Larger wall kits with bigger inverters often cross into G99.
There is usually no separate DNO fee for a straightforward domestic G99 application, but the installer time to prepare the form, single-line diagram and protection settings is real work. Some installers quote G99 as an extra line item. G98 is cheaper and faster because the paperwork is lighter. Confirm what is included in any quote.
No. For systems that need G99, you must wait for DNO approval before energising the battery. Connecting without consent can lead to disconnection notices and insurance problems. That is one practical reason many households prefer a G98-class 5 kWh unit when the capacity is enough for their overnight-to-daytime shift.
Ready for a simple G98 install?
Habo's 5 kWh all-in-one is designed to stay on the G98 notification route. Fully installed from £2,499. Join the waitlist. No deposit, no commitment.
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