Kilowatt

Power vs energy

People use kW and kWh interchangeably but they measure different things. kW is the rate at which energy flows. kWh is the total amount of energy used or stored. The distinction is like the difference between speed (km/h) and distance (km).

A charger rated at 7 kW delivers 7 kWh every hour it’s plugged in. After 8 hours, that’s 56 kWh in the battery. A 50 kW DC charger delivers 50 kWh per hour - so the same 56 kWh goes in about 1 hour and 7 minutes (assuming the car accepts it at that full rate, which drops off as the battery fills).

Why charging speed matters more for some people than others

For daily commuters charging at home overnight, a 7 kW home wallbox is almost always sufficient. An 8-hour charge at 7 kW adds around 400 km of range - far more than most people drive in a day. The question of charging speed really only comes up on long trips, when you need to add significant range in 20–30 minutes at a public DC fast charger.

AC charging power levels

Standard domestic power outlets deliver roughly 2.4 kW (10A × 240V). A dedicated home wallbox on a 32A circuit delivers 7.4 kW on single-phase power. Three-phase wallboxes can reach 11 kW or 22 kW. Most Australian homes are single-phase only, which caps home AC charging at 7.4 kW regardless of the charger installed.

The car’s on-board charger (OBC) also has a rated limit - a car with a 7.4 kW OBC won’t charge faster than 7.4 kW from any AC source, even if a 22 kW charger is connected.

DC charging power levels

DC fast chargers are rated in kW: 25 kW, 50 kW, 75 kW, 150 kW, 175 kW, 350 kW. The actual charging speed you’ll see is limited by whichever is lower: the charger’s rating or the vehicle’s peak DC charging rate.

A vehicle rated for 50 kW DC charging on a 350 kW charger will still only charge at 50 kW. Conversely, a vehicle rated for 200 kW DC on a 50 kW charger is limited to 50 kW at that stop.

Solar systems

Solar panel systems are rated in kilowatts peak (kWp). A 6.6 kW system is rated at 6.6 kW output at peak solar irradiance (roughly 1,000 W/m² at the panel surface, at optimal angle, on a clear day). It won’t always produce 6.6 kW - output varies with weather, time of day, season, and shading - but the kWp figure is the standard for comparisons.