If one quote proposes 3.68kW and another proposes 5kW for the same roof, this is usually why. It is one of the most confusing parts of comparing solar quotes and almost nobody explains it.
The short version
Anything that generates electricity and connects to the public network has to be registered with your distribution network operator, the company that owns the wires in your street. That is not your electricity supplier and you do not choose it. It is determined by where you live.
There are two routes, and the dividing line is 3.68kW per phase:
| Up to 3.68kW per phase | Above 3.68kW per phase | |
|---|---|---|
| Standard | G98 | G99 |
| Permission needed first | No | Yes |
| What happens | Installer notifies the operator within 28 days of commissioning | Application before installation, operator may approve, limit or require works |
| Timescale | None. Install and notify | Can take weeks |
Source: Energy Networks Association. Checked 4 Nov 2026.
Why this produces different quotes
An installer who wants to keep the job simple and fast will design to 3.68kW, because it avoids an application and any risk of the network operator saying no or imposing conditions. An installer proposing 5kW is going the G99 route and accepting the wait.
Neither is wrong. But they are not the same offer, and if you are comparing on price alone you will not notice.
Ask every installer is this a G98 or a G99 connection, have you applied yet, and what happens if the network operator restricts it?
The part that catches people out
The limit applies to generation exported to the network, not to the size of your solar array.
This means a system larger than 3.68kW can sometimes connect under G98 if the inverter output is limited, or if export limitation is set so the system never pushes more than 3.68kW out to the street. Your panels can be bigger than your export limit.
If an installer mentions “export limiting” or “G98 with a limiter”, that is what they are describing. It is legitimate. Just understand that you are capping what you can sell, so check it against what you expect to export. See how much you will export.
Three phase supplies
Most UK homes have a single phase supply. Some larger or newer properties have three phase.
The 3.68kW limit is per phase. So a three phase property can connect around 11kW under G98, which is a considerable difference. If you are not sure which you have, your installer will check at the consumer unit.
Batteries count too
A battery that can export to the grid is also generation as far as the network operator is concerned, and it counts towards the same limit. A 3.68kW solar system plus a battery that can discharge to the grid may together need a G99 application even though the panels alone would not.
This is a common source of confusion when somebody adds a battery later. See expanding an existing system.
What if the network operator says no?
They rarely refuse outright. More often they will:
- Approve it at a lower capacity than you asked for
- Approve it with export limitation
- Approve it subject to network reinforcement works, which can be expensive and are usually the point at which a project is reconsidered
If the area has a lot of existing solar, restrictions are more likely. Your installer should know the local picture.
Plug-in solar is different
Plug-in solar kits of up to 800W have been on sale in Great Britain since 27 Aug 2026 and connect to an ordinary socket. See plug-in solar.
What to ask
- Is this G98 or G99?
- If G99, has the application gone in, and what is the expected timescale?
- Is export limiting being used, and at what level?
- Does my supply run at single or three phase?
- If I add a battery later, will that need a new application?
- What happens to the price and the timescale if the operator restricts us?