This is the question that decides the hardware, and it usually arrives too late in the conversation.
How to tell, in a minute
Look at the meter and the incoming cable.
- One thick tail into one meter — single-phase. This is most UK housing.
- Three tails, or a meter with three sets of terminals — three-phase. Common in larger and older properties, converted farm buildings, and anything with a workshop, a lift or a pool.
If there is a main switch labelled with three fuses, that is three-phase too. When in doubt, photograph the meter position and send it to us.
What it decides
Which inverter. The 5 kW hybrid is single-phase. The 10 kW hybrid is three-phase. They are not interchangeable. A three-phase building fitted with a single-phase inverter gets self-consumption and backup on one phase only, which in practice means the kitchen rides through a power cut and the workshop does not.
Which car charger. 7 kW is the ceiling on a single-phase supply. 11 kW and 22 kW both need three phases. If a faster charger is anywhere in the five-year plan, it belongs in this conversation now rather than after the inverter is on the wall.
Whether load is balanced. Three-phase supplies are rarely balanced in practice. One phase ends up carrying the kitchen while the other two carry very little, and a design based on the site total will miss the phase that is actually near its limit. Measuring per phase is part of any load study we do.
What it does not decide
The battery. Both residential packs are 51.2 V low-voltage LiFePO4 and connect to the inverter rather than to the supply, so the same pack serves either arrangement. Storage capacity does not depend on phase count.
It also does not fix an evening peak. A three-phase house with an unmanaged 11 kW charger has a worse peak than a single-phase house with a scheduled 7 kW one. Headroom only helps if something is using it deliberately.
Upgrading
An upgrade from single-phase to three-phase is arranged through the network operator. It is chargeable work with a lead time usually measured in months, and the price depends almost entirely on how far away the nearest three-phase main is — which is why nobody can quote it from a desk.
Worth arranging if you are committed to an 11 kW or 22 kW charger, a heat pump alongside significant existing load, or three-phase machinery. Rarely worth arranging for storage on its own.
Get the network operator's quotation before committing to a design that depends on the upgrade. We will help you ask for the right thing, and we will design around the supply you already have if the answer comes back expensive.