11 or 22 kW wallbox? Calculate home charging power, time and cost
A 22 kW wallbox will not speed up charging if the car accepts at most 11 kW. Using the BMW i4, we calculate ideal session time and energy cost, then separate both from the full bill.
EvCompass Editorial TeamPublished3 min read
The lowest limit sets the pace
For AC charging, effective power is the lowest of three limits: the car, the wallbox, and the power available to the charging point from the home connection. BMW lists a maximum 11 kW AC rate for the i4 eDrive35. This scenario compares an 11 kW wallbox with a 22 kW unit and assumes the connection can supply 22 kW to the charger. Effective power is the same in both cases: 11 kW.
This is one example with a specific car, not a universal installation recommendation. If your car accepts less power or the home system has less spare capacity, use the lower figure. The connection also has to serve the rest of the home, so check the building's electrical capacity before choosing equipment.
Two wallbox ratings, one vehicle limit
Two wallbox ratings, one vehicle limit
Case
Maximum car AC
Wallbox
Power available to the point
Effective power
Session
Ideal time
11 kW wallbox
11 kW
11 kW
22 kW
11 kW
20 kWh
1.8 h
22 kW wallbox
11 kW
22 kW
22 kW
11 kW
20 kWh
1.8 h
For a 20 kWh session, the calculator returns 1.8 hours of ideal charging at 11 kW. A real session will take longer if other appliances draw part of the available power or if losses and temperature limits apply. The 20 kWh figure is a user-set input here, not battery capacity or a promise for every charging situation.
How to calculate home energy cost
BMW lists combined WLTP consumption for the i4 from 15.1 to 18.6 kWh/100 km. The table uses the upper 18.6 kWh/100 km figure to show a cautious input from the manufacturer's data; it does not describe every driver's actual consumption. URE announced an average 2026 household energy sales price of PLN 495.16/MWh, or PLN 0.49516/kWh before VAT and excise. This is the energy component, not the full rate on a household bill. URE says the bill also includes distribution.
Energy cost in the URE-price scenario
Energy cost in the URE-price scenario
Case
Input
Energy price
Result
Scope
Cost per 100 km
18.6 kWh/100 km — BMW i4 upper WLTP figure
PLN 0.49516/kWh net
PLN 9.21
Energy only; excludes VAT, excise, distribution and fixed charges
Home session
20 kWh
PLN 0.49516/kWh net
PLN 9.90
Energy only; excludes VAT, excise, distribution and fixed charges
Under these inputs, energy alone costs PLN 9.21 per 100 km and PLN 9.90 for a 20 kWh session. The results exclude VAT, excise, distribution charges and fixed fees. For your own accounting, enter the price on your bill or supplier tariff and add the relevant distribution items; allocate fixed fees using a consistent method because they do not automatically rise with each kWh.
Choose between 11 and 22 kW only after checking the car, connection and how the home is used. Change the inputs in the home-charging calculator, compare equipment on the chargers page, and check public rates in the charging-price comparison. See the family specifications in the BMW i4 hub.
The calculation was checked on October 27, 2026. Before making a decision, return to the current vehicle specifications, connection conditions and your energy agreement.
The installation route depends on unit count, rights to the parking bay and the building's electrical system. We show the relevant Polish Act provisions and a separate, explicit time-and-cost scenario.
The NaszEauto application window is closed, and added funding concerns applications already submitted. Here is the current programme status and a dated view of Polish catalogue prices and charging costs.
