G99 is the national rule book for connecting generation to the electricity network when the system is too large for the simpler G98 route. It covers most solar and battery systems above about 3.68 kW of inverter output on a single phase supply. The Energy Networks Association writes it, as Engineering Recommendation G99.
In East Sussex your network operator is UK Power Networks. They own the poles, cables and substations. They are not your electricity supplier, and they are not the council. This guide explains which route your system takes, what the rules say about time, and where the waiting usually happens.
If your system is small enough for the connect and notify route, read the G98 application process instead. This article does not repeat it.
Key Points
- The dividing line is current, not power. G98 covers generation up to and including 16 A per phase. G99 covers everything above that.
- On a normal single phase home supply, 16 A works out at about 3.68 kW. G99 Issue 2 uses a 3.68 kW inverter as its own worked example of that limit.
- A three phase supply has three phases, so the same 16 A limit applies to each one. That is why a larger system on three phase can still sit under the simpler route.
- G99 has three "Small Generation Installation" procedures for domestic sized jobs, called SGI-1, SGI-2 and SGI-3. They differ by how much you can generate and how much you are allowed to export.
- Under SGI-1 you can install first and notify afterwards. Under SGI-2 and SGI-3 you must apply first and wait for the network operator to answer.
- For SGI-2, G99 says the network operator "will provide the results of the assessment within 10 working days of receiving the application".
- For SGI-3, the network operator confirms within 10 working days whether it needs to study your street in more detail.
- The commissioning date you put on the form must be between 10 working days and 3 months from the date you apply.
- After the system is switched on, the commissioning confirmation must be sent no later than 28 days later.
- Above the SGI limits, the system is a Type A generator. There is no fixed answer time in G99 for that route. The network operator decides whether network studies are needed before it can quote.
| Route | Each unit's design capacity | Each unit's registered capacity | Total registered capacity | Export limiter needed | Apply first? |
|---|---|---|---|---|---|
| G98 | 16 A or less | 16 A or less | 16 A or less | No | No, notify after |
| G99 SGI-1 | 32 A or less | 16 A or less | 16 A or less | No | No, notify after |
| G99 SGI-2 | 32 A or less | 16 A or less | 32 A or less | Yes, to 16 A | Yes |
| G99 SGI-3 | 32 A or less | 32 A or less | Under 60 A | Yes, to 32 A | Yes |
Source for the table: ENA EREC G99 Issue 2, section 6.2.2.
Common Misconceptions
"G99 means a big commercial system." No. A normal family home with a 5 kW or 6 kW hybrid inverter is usually on a G99 route.
"You always have to wait for approval before anything happens." Not always. Under SGI-1 the rules let you install and commission first, then notify.
"The panels decide it." They do not. It is the inverter's output that sets the route, not the size of the array. A larger array behind a limited inverter can still sit under a lower threshold.
"The application is the slow bit." Often it is not. Scaffolding, equipment lead times and your own diary usually matter more.
"It is the council." It is not. See above.
Real-World Advice
Our published 17 panel installation in Hailsham is a 7.99 kWp array with a 10 kWh Anker battery. See the Hailsham case study. The customer wrote that the job took six weeks from first contact to finish. That six weeks covered the survey, the design, the grid paperwork, the scaffolding and the install itself.
That is a useful number to hold on to. The grid application is one step inside a wider job. It runs alongside the other steps rather than after them, so it is rarely the thing you wait on at the end.
UK-Specific Considerations
UK Power Networks is the network operator for the whole of East Sussex. The same organisation covers Eastbourne, Polegate, Hailsham, Hastings, St Leonards, Bexhill, Lewes, Seaford, Newhaven and the villages in between. You do not get a different answer by moving from one town to the next.
Your council has no part in this. Wealden District Council, Rother District Council, Eastbourne Borough Council and Lewes District Council deal with planning. The network operator deals with the connection. The two run separately and at the same time.
What does change by address is the state of the local network. Older streets, long rural runs and areas with a lot of existing solar can all mean more checks. That is why G99 lets the network operator say it needs to look harder before it answers.
When This Isn't Right For You
The G99 SGI routes are not for you if any single generating unit is designed for more than 32 A. The same applies if the total registered capacity reaches 60 A per phase. Those systems go down the full Type A application route instead. G99 also caps the total generation on a single phase supply at 17 kW.
Before You Spend Money
Ask your installer which route your design falls under, and get the answer in writing. The reply should name G98, SGI-1, SGI-2, SGI-3 or Type A.
Ask whether your quote assumes an export limit. An export limiter is a condition of SGI-2 and SGI-3, not an optional extra.
Ask whether your supply is single phase or three phase. Most homes here are single phase. It changes the arithmetic.
Ask what happens if the network operator asks for more work. Find out before you sign whether that cost falls to you.
Ask when the application will be submitted. On the apply first routes, SGI-2 and SGI-3, the commissioning date must be at least 10 working days ahead. Early is better.
Frequently Asked Questions
Q: Do I have to wait for permission before my solar is fitted?
A: It depends on the route. Under G98 and SGI-1 you install first and notify afterwards. Under SGI-2 and SGI-3 you apply first and wait for the assessment.
Q: How long does the network operator have to answer?
A: For SGI-2 and SGI-3, G99 says the results or the initial confirmation come within 10 working days of the application.
Q: What happens after the system is switched on?
A: The commissioning confirmation must be submitted no later than 28 days after commissioning.
Q: Can a bigger battery push me from G98 into G99?
A: Yes. Storage counts. G99 adds up the generating units including electricity storage devices when it works out which route applies.
Q: Does a G99 route cost me money?
A: The application itself is part of what your installer handles. If the network operator finds that work is needed on the network, that can be chargeable. Ask before you sign.
Summary
G99 is the connection rule for solar and battery systems above the G98 limit of 16 A per phase. Most East Sussex homes with a 5 kW or 6 kW hybrid inverter land here. The rules give the network operator 10 working days to answer the small installation routes. On the SGI-2 and SGI-3 routes they set the commissioning date between 10 working days and 3 months ahead. They require confirmation within 28 days of switch on. UK Power Networks covers the whole county, so the route is the same in Eastbourne as it is in Bexhill. Your council is not involved.