The most common question solar installers get is: "how much do I need?" And the honest answer is: it depends on your electricity bill, your roof, and what you're planning to plug in over the next five years.
Here's how to think about it — without the upsell.
Start With Your Daily Usage
Check your electricity bill for your daily average consumption in kWh. The typical Australian household uses between 15 and 25 kWh per day, though this varies a lot by state, household size, and whether you have a pool, electric hot water, or an EV.
A rough rule of thumb: every 1kW of solar panels generates about 4–5 kWh of electricity per day in most Australian climates (annual average). So a 6.6kW system produces roughly 26–33 kWh/day on a good day — but you won't capture all of that during winter or on cloudy days.
The 6.6kW Sweet Spot
Australia's most popular system size is 6.6kW — typically 16–18 panels at around 370–400W each. It's popular for good reason: it fits comfortably within the standard single-phase inverter limit (usually 5kW inverter with 6.6kW of panels, which is allowed under Australian grid rules), it suits most average-usage households, and the rebate per dollar spent is strong.
If your daily usage is under 20 kWh and you're not planning to add an EV or heat pump, a 6.6kW system is probably enough. If your bills are consistently high, or you're planning to go all-electric, consider 8–10kW from the start.
Why Bigger Can Be Smarter
Many homeowners regret going too small. Here's why:
- Feed-in tariffs are low — typically 3–10 cents per kWh in 2026. Excess solar you export to the grid earns very little. Self-consumption is where you save real money.
- Future loads — adding an EV can add 5–15 kWh/day to your consumption. A heat pump hot water system adds 1–3 kWh/day. If you're buying for the next 10 years, size for what's coming.
- The rebate doesn't scale linearly forever — but there are real economies of scale when adding a couple of extra panels to an existing install design.
Roof Space and Orientation
North-facing panels generate the most power in Australia. East and west-facing panels produce roughly 15–20% less, but they generate power earlier in the morning and later in the afternoon, which can actually suit households that use more power in the morning and evening.
If you have shading — from trees, a chimney, a neighbouring building — your installer should model the impact using software like PVSell or Solargraf. Shade on even one panel can drag down output for the whole string if you have a standard string inverter. Microinverters or DC optimisers solve this, but add cost.
Don't Just Take the Installer's Word for It
Ask every installer to show you their production estimate based on your actual roof orientation, your local climate data, and your average daily usage. A reputable installer will use BOM solar irradiance data and specialist quoting software — not a back-of-envelope calculation.
The easiest way to know if you're being sized correctly is to work backwards from your bill. Upload your electricity bill to GridBeater and we'll tell you exactly what system size makes sense for your actual usage pattern — and what it would save you per year.
Upload your bill and find out what size solar system suits you → Free at GridBeater