Home charging mostly happens overnight, so a super-fast wallbox is rarely needed. It still pays to choose the power deliberately, because it decides what the installation costs and how heavily your connection is loaded.
What decides what you need?
Three things: how much you drive, how much AC power your car can take, and what your electrical connection allows. The lowest of the three wins. An 11 kW wallbox on a car that only accepts 7.4 kW charges at 7.4 kW.
Work out what you need per day
Take a car that uses 18 kWh per 100 km. Drive 50 km a day and you need about 9 kWh. Charging losses come on top, so allow a little more.
- At 3.7 kW that takes about 2.5 hours.
- At 7.4 kW, a little under 1.5 hours.
- At 11 kW, about 50 minutes.
Your car easily sits on the charger for 8 hours overnight. In that time 3.7 kW delivers around 30 kWh, good for well over 160 km. At 7.4 kW it is roughly double. For a normal working week, a modest power level is usually enough.
When more power does help
Say your battery is 60 kWh and you want to go from 20% to 100%. That is 48 kWh.
- At 3.7 kW you are charging for about 13 hours.
- At 7.4 kW, about 6.5 hours.
- At 11 kW, a little over 4 hours.
That difference matters if you often park at home nearly empty, get back late in the evening and leave early in the morning, or share a wallbox or a connection between two cars. Then 3.7 kW gets tight quickly.
What can your car do?
The onboard charger sets the AC maximum. Many cars charge at 7.4 kW or 11 kW, some at less. A 22 kW wallbox will not charge them any faster. Check the manual for the maximum AC speed.
Mind the number of phases too. 7.4 kW comes from one phase, 11 kW from three. If your car only charges on a single phase, it never goes above 7.4 kW, even on a three-phase wallbox.
What can your connection do?
An 11 kW wallbox needs a three-phase connection and draws roughly 16 A per phase. Your other consumption adds to that: oven, heat pump, tumble dryer. A certified installer checks what your connection can handle and whether the wiring in your meter cupboard is up to it.
Also ask whether the wallbox can be set to a lower power. Many models allow it. That way you buy a more capable unit, run it at a lower setting first, and raise it later if your situation changes.
The capacity tariff
Part of your grid tariff depends on your highest quarter-hour peak of the month. An 11 kW wallbox can push that peak up a long way if it runs at the same time as the hob, heat pump and dryer. A 3.7 kW wallbox counts for much less, but it also charges much more slowly.
Schedule your session for late in the evening, or pick a wallbox with dynamic load balancing, which turns its power down when the rest of the house draws a lot. How heavily the peak weighs depends on your network operator’s tariffs, and those change. Check your own bill.
Common mistakes
- Looking only at the maximum speed. A car that drives 30 km a day barely notices the difference between 7.4 and 11 kW.
- Buying 22 kW when the car and the connection do not allow it. You pay for power you never use.
- Forgetting the cable run. A long distance between the meter cupboard and the wallbox can push up the cost, whatever the power.
- Ignoring a second car. Are you considering another one within a few years? Tell your installer right away.
When this does not apply
Do you have solar panels and mostly charge during the day on your own surplus? Then what your panels produce sets your charging speed, not the wallbox power. Read more in our guide to charging with solar panels. If you only charge in public, for example because you have no parking space of your own, none of this applies.
So which power should you choose?
If you drive little to a moderate amount and have one car, 7.4 kW is plenty, and often 3.7 kW is too. Choose 11 kW if your car can take it and you drive a lot or have two cars. Do not go for 22 kW without a clear reason. To compare actual units, start with how to choose a wallbox.