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SolarSingle phase or three phase, and what it changes
One look in the meter cupboard tells you which supply your home has. It is the single biggest thing deciding how much solar and battery you can fit before anyone has to ask permission.
Updated 4 August 2026 · from the OVO Solar & Battery team
The short answer
Most UK homes are single phase. One main fuse at the cut-out, two cables going into it. Three phase homes have three fuses, usually 100A each, and four cables. That one difference decides how much generation and storage capacity you can connect before your network operator has to approve it: 3.68kW of inverter on single phase, 11.04kW on three phase.
The limit is on the inverter, not the panels
Both thresholds are written around the AC rating of the inverter per phase. They are not a cap on how many panels go on the roof, and they are not a cap on battery capacity in kWh. A well designed single phase system routinely carries noticeably more panel capacity than 3.68kW.
How to check yours, in about a minute
Find the meter and the main fuse
Your supply arrives through a cut-out box, usually beside the meter in a cupboard, a hallway or an outside box. It is sealed and belongs to your network operator, so this is a looking job only. Do not open anything or remove any covers.
Count the fuses
One large cut-out fuse means single phase, which is what the large majority of UK homes have. Three fuses, typically 100A each, means three phase.
Count the cables
Single phase runs on two wires, one live and one neutral. Three phase runs on four, three lives and one neutral.
Read the meter markings
A meter labelled L1, L2 and L3 is a three phase meter. If none of that is clear, stop there. Take a photo and show it on your design call, and your local OVO expert will tell you in seconds.
| What you are looking at | Single phase | Three phase |
|---|---|---|
| Fuses at the cut-out | One | Three, usually 100A each |
| Cables into the cut-out | Two: one live, one neutral | Four: three lives, one neutral |
| Meter markings | No phase labels | L1, L2 and L3 |
| Inverter capacity with no prior permission | 3.68kW | 11.04kW |
| Connection route at that size | G98, fit then notify | G98, fit then notify |
| Above that capacity | G99 application first | G99 application first |
Fuse ratings vary by property. The inverter figures are the connect and notify thresholds in the industry connection rules, and they apply per phase.
What it changes: how much you can fit before anyone asks permission
Up to 3.68kW of inverter capacity per phase, which is 16A per phase, the job runs under G98. That is a connect and notify process: the system is fitted first, then the form goes to the network operator within 28 days of commissioning. Completed properly, it cannot be rejected. Nothing waits on anybody.
Above that, it is G99, and the order reverses. The application goes in and the network operator has to approve the connection before the installation happens. A standard determination usually takes 4 to 8 weeks, fast track routes come back in around 2 weeks, and complex cases can stretch to 12. The application itself is free, although some installers charge an admin fee, and in rare cases the operator asks for network reinforcement work to be paid for.
You never file any of this
In a standard installation the installer handles G98 and G99 from end to end. Your Distribution Network Operator is the company that owns the cables and substations in your street, not your energy supplier. Great Britain has 14 licensed operator areas run by six groups, and you can identify yours from the first two digits on the bottom line of your MPAN, or by calling 105.
Not sure what you have? Show it on a free 45 minute video design with your local OVO expert, with no home visit and a written quote on the call.
Get your free quote →What it does not change
Being single phase is not a small system sentence. Because the threshold measures the inverter's AC rating, arrays are routinely built larger than the inverter that serves them. Industry practice puts that ratio somewhere between 1.10 and 1.30, most commonly 1.15 to 1.25, and roughly 4kWp of panels on a 3.68kW inverter has been the standard UK single phase configuration for years. UK roofs rarely hit datasheet test conditions, so the periods when output is capped are short, and a right sized inverter also starts generating earlier in weak light.
- How many panels fit. That is roof space, pitch, orientation and shading.
- How big your battery should be. That comes from what you use after dark, not from your supply.
- Which export rate you qualify for. That is set by your supplier and by how the system was installed.
- How long the work takes on the day, or whether you need scaffolding.
If you have three phase
You have real headroom, so use it in the design rather than the sales pitch. The point of the extra capacity is filling the roof in one visit, because the expensive parts of a solar job barely move with system size. Our cost guide shows how the price per kWp falls as the system grows. Surplus generation is then income rather than spillage, on the conditions set out in our export rate guide.
If a G99 comes back with conditions
- Pay for the network reinforcement the operator has specified, if the numbers justify it.
- Cap the inverter at 3.68kW with export limitation, and keep the array size you wanted.
- Decline the connection and redesign around what the site will take today.
- Reapply later, since local network capacity changes as the operator reinforces the area.
Option two is the one most homeowners land on, and it is less of a compromise than it sounds. Electricity you use yourself displaces import at 26.11p per kWh under the July to September 2026 price cap, so a battery holding generation back for the evening does more for the bill than the last kilowatt of export ever would. That sequencing is set out in our solar and battery strategy.
Every area has a named OVO expert who checks all of this before you commit to anything. Find yours on the coverage page.
Get your free quote →OVO SEG Install Exclusive pays up to 20p per kWh where OVO installs both the solar and the battery, or 15p per kWh for solar only. The exclusive rates require you to take your electricity supply from OVO and apply to systems under 30kW. OVO's standard SEG rate of 4p per kWh is open to customers of any supplier. Rates correct at August 2026 and subject to change.
Phase questions, answered
How do I know if my house is three phase?
Look at the cut-out box next to your meter without opening it. One main fuse and two cables is single phase, which covers the large majority of UK homes. Three fuses, usually 100A each, and four cables is three phase. A meter marked L1, L2 and L3 confirms it. If you cannot see clearly, photograph the cupboard and show it on your design call.
Can I install more than 3.68kW of solar on a single phase home?
Yes. The 3.68kW threshold is the inverter's AC rating, not the panel capacity, so you can fit meaningfully more kWp of panels and still stay on the fit then notify G98 route. If the design genuinely needs a larger inverter, that is a G99 application rather than a refusal.
How long does a G99 application take?
A standard determination usually runs 4 to 8 weeks. Fast track routes can come back in about 2 weeks, and complex cases occasionally reach 12. The application is free, though some installers charge an admin fee. Your installer submits it and chases it, so nothing lands on you.
Does three phase mean I can have a bigger battery?
It gives you more headroom on the equipment side, because the connection threshold is set per phase. The physical size of the battery is decided by how much electricity you use outside daylight hours, which is a different question entirely and the one your design call actually answers.
Can I upgrade from single phase to three phase?
That is a job for your network operator rather than your installer, and for a domestic solar and battery system it is very rarely the right answer. A single phase supply comfortably supports a full roof of panels and a battery. Your local OVO expert will say plainly if your design is one of the exceptions.
Is three phase better?
Not by itself. It is simply a different supply arrangement, and most UK homes work perfectly well without it. It matters for solar only because the connect and notify capacity limit is higher, which occasionally removes a wait from the timeline.
Figures and specifications in this guide are sourced below and were checked on the date shown. Rates and product specifications change; we confirm the current picture on your free design call.
Sources
- Single phase and three phase supplies: fuses, cables and L1, L2, L3 meter markings ukpowernetworks.co.uk, uk.jackery.com
- G98 threshold of 3.68kW per phase, connect and notify, 28 day notification sunsave.energy
- G99 timescales, free application, and the options where a connection is refused or conditioned sunsave.energy
- Inverter capacity limits of 3.68kW single phase and 11.04kW three phase spiritenergy.co.uk
- Distribution Network Operator areas, the MPAN check and the 105 number ovoenergy.com, energynetworks.org
- Inverter loading ratios of 1.10 to 1.30 and UK clipping behaviour aurorasolar.com, spiritenergy.co.uk
- Capped average electricity unit rate of 26.11p per kWh, 1 July to 30 September 2026 ofgem.gov.uk
- OVO SEG rates and their conditions ovoenergy.com
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