Kilowatt-Hour

The unit that runs through everything

The kilowatt-hour appears everywhere in home energy: it’s what electricity retailers charge for on your bill, what’s stored in your home battery and EV, and what solar panels generate. Understanding it removes most of the confusion around energy comparisons.

One kilowatt-hour is the amount of energy used when a 1,000-watt device runs for exactly one hour. A 2.4 kW electric kettle boiling for 25 minutes uses 1 kWh. A 7 kW EV charger running for about 8.5 minutes delivers 1 kWh to the car.

In an EV battery

Battery size is expressed in kWh. The figure tells you roughly how much energy the pack can store and release under controlled conditions. Common sizes in Australian EVs currently range from around 45 kWh (small commuter EVs) to 100 kWh (large SUVs like the Kia EV9).

To get a rough sense of range from a battery size, divide by the car’s consumption in kWh/100 km. A car using 16 kWh/100 km with a 77 kWh battery has roughly 480 km of range - less the buffers the BMS reserves and real-world efficiency variation.

A useful reference point: 1 kWh of electricity takes an average EV about 6–7 km. A 77 kWh battery holds the equivalent energy of around 6.7 litres of petrol, but an EV converts that energy to motion 3–4× more efficiently than a combustion engine, which is why the running costs are so much lower.

On your electricity bill

In Australia, electricity is priced per kWh. A standard flat rate is currently around 28–40¢/kWh depending on the state and retailer, with off-peak time-of-use rates typically running 15–22¢/kWh overnight.

If you charge an EV with a 70 kWh usable battery from flat to full on a standard 32¢/kWh rate, you’ll pay roughly $22.40. The equivalent petrol cost for the same 400–450 km would be $75–90 at current prices. That’s the economics of EV ownership in a single comparison.

Usable vs total capacity

Manufacturers quote two different kWh figures, though not always clearly. The gross capacity is the total size of the cells. The net or usable capacity is what you can actually access - typically 5–10% less than gross, because the BMS reserves buffers at both ends.

When comparing vehicles, use the net/usable figure. A car with 82 kWh gross and 77 kWh net has meaningfully less accessible range than its headline number suggests.

Solar and battery storage

The same unit applies to home solar and battery storage. A 13.5 kWh Powerwall holds 13.5 kWh of usable energy - enough to power an average Australian household for roughly 12–14 hours overnight. A 6.6 kW solar system on a typical Sydney day generates around 24–28 kWh of electricity.