kW vs kWh: solar size, battery size and your bill, explained

What's the difference between kW and kWh?

The difference between kW and kWh is the difference between a flow and an amount. Think of a tap filling a bucket. kW is how far the tap is open: the flow at any moment. kWh is how much water ends up in the bucket. Run a 1 kW heater for one hour and you use 1 kWh. Run a 2 kW kettle for half an hour and you also use 1 kWh.

Are solar panels measured in kW or kWh?

Solar panels are rated in kW: a “6.6 kW system” describes the combined peak output of the panels in ideal conditions: for example, fifteen 440 W panels. It rarely runs at that peak. What matters for savings is how many kWh it produces over a year, which depends on where you live, the roof's direction and tilt, and shade.

These are averages: a sunny summer day produces far more, a grey winter day far less. They're based on the Clean Energy Regulator's zone ratings, the same figures used to work out the solar rebate.

What does an inverter's kW rating mean?

The inverter converts the panels' DC power into AC power for your home, and is also rated in kW. It's common, and allowed, for the panels to be up to a third bigger than the inverter (for example 6.6 kW of panels on a 5 kW inverter), because panels rarely reach their peak. Your network may also limit how much you can export, often around 5 kW per phase, which is another reason inverters are often 5 kW.

Are batteries measured in kW or kWh?

A battery is rated in both kWh and kW, and both numbers matter:

• Capacity, in kWh: how much energy it stores. Look for usable capacity, what you can actually draw out, not the larger “nominal” figure. The federal battery rebate is also based on usable kWh, at the full rate up to 14 kWh.
• Power, in kW: how much it can supply at once. A 13.5 kWh battery with 5 kW continuous power can run a 2 kW air conditioner and a 2 kW oven together, but not a 7 kW induction cooktop on full at the same time. For blackout backup, the kW figure matters as much as the kWh.

A full 10 kWh battery could run a 1 kW load for about 10 hours, or a 5 kW load for about 2 hours, less a little lost in conversion. See what size battery you need.

What does kWh mean on your power bill?

Retailers charge you per kWh of energy you import (the usage charge, often 25 to 45 cents), plus a daily supply charge. They pay you a feed-in tariff per kWh you export (4c is typical now). Your bill shows your usage in kWh for the billing period; divide by the number of days to get your average daily use. As a rough guide, a NSW household paying $600 a quarter uses around 15 kWh a day.

Some business and time-of-use bills also have a demand charge, priced per kW (or kVA): it's based on your highest rate of use at any one time, not the total. Batteries can help reduce it. For a business roof, see commercial solar in 2026.

Putting it together

• Size solar (kW) so that over a year it produces roughly what you use (kWh), allowing for what you'll export.
• Size a battery (kWh) to what you use after dark, and check its power (kW) covers what you want to run at once.
• Judge savings in kWh and dollars: kWh of grid power you no longer buy, times what you pay per kWh.

Figures as of 26 September 2026.