How Much Solar Do I Really Need? Sizing Your System for an Australian Home

Solar system sizing in Australia gets framed by sales people as “more is better” and by online calculators as a one-size-fits-all “6.6kW for everyone.” Neither is quite right. The right system for your home depends on your real usage pattern, your roof, and what you plan to add later — battery, EV charger, or pool heat pump. Here’s how a Clean Energy Council Approved Retailer actually sizes a system in 2026.

Why “6.6kW” became the default

For years, 6.6kW was the magic number because it matched a 5kW inverter limit and maximised STC rebate value per dollar. It’s still a sensible baseline for a 3–4 person Australian home with a single-phase connection.

But the real answer depends on your annual usage in kWh, not your household size.

The right way to size: start with your bill

Look at your most recent quarterly electricity bill. Find the total kWh used over the billing period. Multiply by 4 to get your annual consumption.

• Under 4,000 kWh/year → 4.4–6.6kW system.
• 4,000–6,500 kWh/year → 6.6–8.8kW system.
• 6,500–9,500 kWh/year → 8.8–10kW system.
• 9,500+ kWh/year → 10kW+ system, three-phase usually required for larger.

This gives you a starting bracket. Then we adjust for roof aspect, shading, and what you plan to add.

Does roof orientation matter?

Yes, but less dramatically than people think.

• North-facing: peak output. Reference point.
• East or west: 10–15% less annual generation than north, but more morning or afternoon output — better if you use power during those times.
• South-facing: 20–30% less annual generation. Often only worth it if your north roof is small.
• Split-orientation systems: dual-array (east + west) can actually outperform a single north array for self-consumption, because output is more evenly spread across the day.

We assess your actual roof when we scope your system, not from satellite alone. Shading from trees, neighbouring buildings, and Adelaide’s afternoon sun angles change the math.

What if I’m planning a battery later?

If a battery is on the roadmap (federal incentives and state rebates make this likely for SA, VIC, NSW households), size the solar to cover both daytime usage and battery charging.

A whole-home Fox ESS stack typically lands at 21kWh usable or more — enough to actually carry the evening peak and overnight base load rather than running flat at 9pm. To fully charge a battery that size from solar alongside your daytime base load on a winter day, you generally want a panel array 1.5–2x larger than a solar-only system would need. That means most homes pairing solar with a battery sit at 8.8kW–10kW of panels rather than the bare 6.6kW minimum.

Our hybrid-ready inverters are spec’d by default, so adding a Fox ESS battery later doesn’t require swapping the inverter.

What about an EV charger?

If an EV is on the cards, your usage will jump. A typical Australian commute (40km/day) adds around 2,500 kWh/year to your bill. We add that to the sizing calculation upfront so the system isn’t undersized when the car shows up.

Solar-aware EV chargers can prioritise charging from your solar generation rather than the grid — letting you effectively drive on free kilometres during the day.

What about hot water?

If you’re on electric storage, switching to a heat pump hot water system cuts hot water power use by up to 75%. That changes your sizing equation — a smaller solar system can cover the load.

If you stay on gas hot water (or already have a heat pump), no adjustment needed.

The export-limit catch

In most states there’s a limit on how much solar power you can export back to the grid — typically 5kW per phase on residential. If you install 10kW of panels on a single-phase home, you’re capped at 5kW export, with the rest “curtailed” (clipped by your inverter) whenever the home isn’t using it.

This isn’t a deal-breaker — it just means the value of those extra kW depends heavily on whether you’re home during the day, whether you have a battery, and whether you’re planning an EV. Three-phase homes have a higher export limit (usually 5kW per phase = 15kW total) which is why bigger systems are common in larger or three-phase houses.

How does eHomes actually size your system?

We work backwards from three numbers: your real annual usage in kWh, your roof’s usable area and aspect, and your 5-year roadmap (battery, EV, hot water swap). We don’t sell a package off a shelf — every quote is sized from those inputs, with the STC rebate factored in at the point we quote.

Get a sized quote for your home

The fastest way to find out what fits your house is to grab a free quote — postcode, quarterly bill, and roof type is enough. We come back with system options, real prices including the STC rebate, and a payback figure for each.