How much solar do I need?
Your power bill is the best place to start. Then your roof, your budget and your plans set the final size.
Work out your daily use from your bill, then size solar around when you use power, your roof, your budget and future loads like an EV or heat pump. Australian homes use 11 to 23kWh a day on average. A 6.6kW system is common, but the national new-system average was 10.5kW in the June 2026 quarter.
Answered by Chris Bull, Managing Director Chris Bull on LinkedIn (opens in a new tab).
Start with your bill
Find your average daily use in kilowatt-hours on your bill. It is the total used divided by the days in the billing period. Energy.gov.au says Australian homes use 11 to 23kWh a day on average.
Look at summer and winter bills, because both your usage and your solar output change. If you have a smart meter, ask for 12 months of interval data. It shows when you use power, and that matters as much as how much.
Then look at the roof
One residential panel often takes about 1.7 square metres. A 6.6kW system needs around 29 to 32 square metres, depending on the panels.
Direction, pitch and shade all affect output. The free SunSPOT calculator shows how much sunny roof you have and how many panels could fit.
How many panels is that?
Divide the system size in watts by the panel rating. The government’s example is 19 panels at 350 watts, which makes 6.65kW. Higher-rated panels mean fewer panels for the same size.
- 6kW at 350 watts: about 17 panels
- 6.6kW at 350 watts: 19 panels
- 10kW at 350 watts: about 29 panels
Why 6.6kW is so common
A 6.6kW system is often paired with a 5kW inverter. Panels rarely hit their full rating, so this can make good economic sense. Your system must stay within the inverter maker’s limits to get the STC discount.
Many homes now go bigger. SA Power Networks’ standard allows up to 10kVA of solar inverter per phase, with export limits. Bigger systems still need a reason, such as high daytime use or a battery to fill.
Size for the home you will have
Energy.gov.au says a rooftop system lasts 20 years or more, so plan ahead. Tell your installer about any of these.
- An EV
- Switching from gas to electric hot water, heating or cooking
- A pool or spa
- More air conditioning use
- An extension
- A battery now or later
Remember how exports are paid
With retailer feed-in tariffs from zero to 5.5 cents per kWh at 30 June 2026, extra panels pay best if you can use the power. That can be through daytime loads, a battery or an EV. See what you will be paid for exports.
Let us size it with you
We read your bill, inspect your roof and switchboard, and show what different sizes would do at a 90-minute in-home consultation. Book a bill audit.
Common questions
What is the 20% rule for solar panels?
It is a rule of thumb, not a rule. We did not find it in the government’s solar guide, and people use it in different ways. Size from your own bill instead.
Is 10kW solar enough to run a house?
It can generate more than many homes use in a day, but it cannot run a home at night without a battery or grid power. Timing matters as much as size.
How big a solar system do I need for my house?
Use your daily kWh, your roof space and your future plans. SunSPOT gives a free estimate, and we can refine it on site.
How many solar panels do I need for a 6kW system?
Divide 6,000 by the panel’s watt rating. At 350 watts, that is about 17 panels.
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