The question arrives late in almost every project, usually as a surprise: is the house single-phase or three-phase? It sounds like a detail. It decides the hardware.
The distinction, briefly
A single-phase supply brings one live conductor into the building. A three-phase supply brings three, each peaking a third of a cycle apart. The useful consequence is not that you get three times as much power — you may or may not — but that a large load can be shared evenly across all three instead of sitting on one.
Most homes in the UK are single-phase. Larger houses, older properties with workshops, small commercial units and anything with a lift, a pool or serious machinery are often three-phase already, and the owner frequently does not know.
Check the meter and the incoming cable. One thick tail and one meter is single-phase. Three tails, or a meter with three sets of terminals, is three-phase.
What it decides
Which inverter. Our 5 kW hybrid is single-phase. Our 10 kW hybrid is three-phase. They are not interchangeable, and a three-phase building fitted with a single-phase inverter has backup and self-consumption on one phase only — which usually means the kitchen works in a power cut and the workshop does not.
Which car charger. 7 kW is the ceiling on single-phase. An 11 kW charger needs three phases, and 22 kW certainly does. If a fast charger is on the five-year plan, it belongs in the supply conversation now rather than after the storage is on the wall.
How balanced the building is. Three-phase supplies are rarely balanced in practice — one phase ends up carrying the kitchen and the other two carry very little. Part of a load study is measuring per phase, because a design based on the total misses the phase that is actually near its limit.
What it does not change
The battery. Both residential packs are 51.2 V low-voltage LiFePO4 and connect to the inverter, not to the supply, so the same pack serves either arrangement. Nothing about storage capacity depends on phase count.
It also does not change the physics of the evening peak. A three-phase house with an unmanaged 11 kW charger has a worse peak than a single-phase house with a 7 kW one. More capacity is only an advantage if something is scheduling it.
Can you upgrade?
Usually, yes. An upgrade from single to three-phase is arranged through the network operator, and it is chargeable work with a lead time — often measured in months rather than weeks, and the cost depends almost entirely on how far away the nearest three-phase main is.
It is worth doing if you are planning an 11 kW or 22 kW charger, a heat pump alongside significant existing load, or a workshop with three-phase machinery. It is rarely worth doing for storage alone.
The honest version: get a quotation from the network operator before you commit to a system design that depends on it. We will help you ask for the right thing, and we will design around the supply you have if the answer comes back expensive.