Features → How fast a charger

How fast a charger do you need?

Wallboxes are sold on their top speed. For a car that sleeps on your drive every night, the top speed is close to irrelevant — and if you are charging on solar, the specification that actually matters is the one nobody prints.

The overnight arithmetic

A typical day's driving is twenty to fifty kilometres, which is somewhere around 4 to 9 kWh. A single-phase 7 kW wallbox replaces that in a bit over an hour. You are asleep for eight.

Faster charging does not get you more range; it gets you the same range sooner, during hours you were not using the car. The exceptions are real but narrow: you drive a very long way most days, several cars share one charger, or your off-peak window is genuinely short.

Why your supply usually decides anyway

A 22 kW wallbox needs a three-phase supply and the headroom to use it. Most homes on a single phase are capped around 7 kW whatever the wallbox claims, and plenty of houses cannot give a car its full share without something else going off.

This is what the combined limit in Sunplug is about: the ceiling is not the wallbox's rating but what your installation can actually deliver with the kettle on. Buying a faster wallbox does not raise it.

On a solar roof, the floor is the specification

Here is the part specific to charging on sunshine, and it inverts the usual advice.

Solar charging spends most of its time at the bottom of the range. A 3 kW surplus on a mixed afternoon is a good surplus, and what decides whether you can use it is the lowest rate the chain will hold — not the highest it can reach. A wallbox that will sit steadily at 6 A captures afternoons that one dropping out below 10 A simply throws away.

Two floors are in play and the lower one wins:

• The car's. Most refuse to charge meaningfully below about 5 or 6 A. This is a property of the vehicle and no wallbox fixes it.
• The wallbox's. An OCPP charger typically will not signal below 6 A. Some are worse in practice than on paper.

So on a single phase at 230 V, useful charging starts around 1.2 to 1.4 kW. Below that, there is nothing anyone's software can do — Sunplug waits rather than pretending.

One fast charger or two slower ones?

For a two-car household on solar, two slower chargers usually beat one fast one, and the reason is the floor again. With one charger you are moving a cable and only one car benefits from any given afternoon. With two, both cars can sit on a modest surplus at once — provided the supply can seat them, which is its own question.

It also removes the "which car is on the lead" problem entirely. That one →

Three-phase

Three-phase charging raises both the ceiling and the floor, which for solar is a mixed blessing rather than an upgrade. That argument has its own page, not yet published.

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