Wallbox and solar: charge from your surplus instead of selling it cheap

Where the gain is

Solar generates most when nobody is home and demand is lowest. The surplus goes to the grid at a feed-in price well below what you pay to import.

An EV is the ideal customer for that surplus. It's a big battery in no hurry. A smart wallbox can watch how much is currently flowing out and throttle or raise charging so the car takes exactly what you'd otherwise export.

What the wallbox needs for it

This is where it usually breaks down, because "smart" alone isn't enough. It needs:

• Metering on the main supply. The wallbox has to know the live flow at the building's intake — what's being generated, what the rest of the house draws, and what's spilling over. Without that it has nothing to regulate against. Sometimes a metering module suffices; elsewhere a separate meter is added.
• Compatibility with your inverter. Not every wallbox talks to every inverter. Some manufacturers run closed ecosystems; others use open interfaces.
• Phase control. Surplus is often small — a few hundred watts. The wallbox must be able to go low and ideally switch to single phase, otherwise charging keeps starting and stopping.

This is exactly why we recommend a survey before you buy the charger. We've seen a bargain wallbox that couldn't manage surplus with the installed inverter more than once — discovered only after fitting.

Three modes to choose between

• Surplus only. Charges purely from what would be exported. Cheapest to run, but in winter and cloud the car charges slowly or not at all.
• Surplus plus top-up. Takes surplus and tops up from the grid to a set minimum, so the car is always usable in the morning. The most practical option.
• Full power. Conventional charging regardless of generation — for when you need to leave.

You switch in the app or schedule it. We set it up at handover and walk you through what each option means.

Why this saves more than a higher rating

The difference between an 11 and a 22 kW wallbox saves you nothing at home — the car is parked overnight and finishes either way. The difference between charging from your own surplus and from imported electricity shows up on every kilowatt-hour.

Run a few thousand kilometres a year off your own roof and it shows on the bill far more than any number on the charger's label.

And a note on grants

It's no accident that grant schemes list a wallbox mainly in combination with solar and conditional on load management. If you're planning panels and a wallbox, it pays to do both at once — more in the Grants section.