6.6kW vs 10kW vs 13.3kW: What Size Solar System Does Your Home Need?

The most common question we get from homeowners considering solar is: "What size system do I need?" It's also the question most commonly answered poorly — either with a one-size-fits-all recommendation, or with a system sized for current usage without any thought for how your needs might change.

Here's how to think about it properly.

Start With Your Electricity Bill

Your electricity bill shows your consumption in kWh. The average Australian home uses about 18–20 kWh per day, but there's enormous variation — a 2-person apartment might use 8 kWh/day while a 5-person home with a pool might use 35 kWh/day.

Find the total kWh on your last quarterly bill and divide by 90 to get your daily average. This is your starting point.

How Much Does Each System Produce?

In Sydney (which receives excellent solar irradiance), you can expect:

System Size	Avg. Daily Output	Best Suited To
6.6 kW	26–28 kWh	2–3 bedroom homes, 2–3 people
10 kW	38–42 kWh	3–4 bedroom homes, families
13.3 kW	50–55 kWh	Large homes, pools, EV charging

Why "Match Your Current Usage" Is Incomplete Advice

Many installers will size a system to exactly match your current consumption. This is reasonable but incomplete. Think about:

• Are you planning to get an EV? Charging a typical EV adds 10–15 kWh/day to your consumption. If you're buying an EV in the next few years, size your system for that now.
• Are you switching from gas to electric? An electric hot water heat pump or induction cooktop will increase consumption. Size accordingly.
• Are you adding a battery? A larger solar system paired with a battery increases your self-consumption rate dramatically and improves the battery's return on investment.
• Is your family growing? More people means more consumption. It's cheaper to install a larger system once than to retrofit more panels later.

Roof Space: The Practical Constraint

Each modern solar panel is around 1.7m x 1.1m and produces around 400–430W. A 6.6kW system needs approximately 15–16 panels; a 10kW system needs around 23–24 panels. Your north-facing roof space (and any east/west facing areas) determines your practical upper limit.

A professional site assessment — which Betawatt provides free — will map your roof space, calculate shading at different times of year, and recommend the optimal layout for your specific property.

The 6.6kW Question: Why Is It the Most Common?

The 6.6kW system became the default recommendation partly for historical regulatory reasons (many networks limited single-phase export to 5kW, and a 6.6kW panel array with a 5kW inverter was a workaround). Those restrictions have changed in most of Sydney, and 10kW systems are now available to more homeowners than many people realise.

If your roof space and network connection allow it, a 10kW system is worth serious consideration — particularly for households with high usage, an EV, or plans to add a battery.