What Size Solar System Do You Need?

Electricity Consumption

Your bill size is the starting point. A household using 20kWh/day needs a different system than one using 40kWh/day. Check your bill for daily average usage — it's usually on page 2.

Daytime Usage Patterns

Solar generates during the day. If you work from home, run AC during summer days, or have a pool pump, you'll use more solar directly — which means bigger savings per kW installed.

Available Roof Space

Each panel needs about 1.7m² of clear, unshaded roof. A 6.6kW system needs roughly 26m² of suitable roof. Shading from trees or neighbouring buildings reduces effective space.

Future Plans

Planning to get an EV, pool, or switch from gas to electric? Size your system for your future usage, not just current. Adding an EV can add 8–12kWh/day to your consumption.

Battery Plans

If you plan to add a battery, a slightly larger system makes sense — the extra generation charges your battery instead of being exported at low feed-in rates.

Export Limits

Some networks cap how much you can export (typically 5kW). A very large system may be curtailed during peak sun hours. Check with your distributor or ask your installer about local limits.

Going too small to save money

A 5kW system is only marginally cheaper than a 6.6kW system, but the 6.6kW generates 20–30% more electricity. The cost-per-kW is better on larger systems, so sizing up usually improves your return.

Ignoring future consumption changes

If you're planning to get an electric car, heat pump, or pool in the next 5 years, factor that in now. Adding panels later costs more per kW than getting them upfront.

Not accounting for shading

Installers sometimes quote system sizes based on total roof area without properly assessing shade. A 10kW system that's 30% shaded performs like a 7kW system — but costs like a 10kW.

Oversizing without a battery

If you don't have a battery and your feed-in tariff is low (3–5c/kWh), a very large system may not save you proportionally more. The excess generation gets exported for very little return.

Why is 6.6kW the most popular size?

It hits the sweet spot — big enough for most 3–4 person households, affordable ($4,000–$6,500 after rebates), and sits just under the 5kW inverter export limit that many networks impose. A 6.6kW panel array paired with a 5kW inverter is Australia's most cost-effective residential system.

Can I add more panels later?

Technically yes, but it's not ideal. A second installation visit costs $1,000–$2,000+ in labour and admin, and you may need to upgrade your inverter. You also get fewer STCs per panel on a retrofit than on a new install. It's almost always cheaper to get the right size upfront.

What if my roof can only fit a smaller system?

Smaller systems still deliver strong returns — a 5kW system saves $1,000–$1,600 per year. If roof space is limited, consider higher-efficiency panels (like 400W+ panels) which generate more per square metre, or microinverters which optimise shaded or oddly-angled panels.

How does system size affect my payback period?

The payback period is surprisingly similar across sizes (3–5 years) because larger systems cost more but also save more. The key difference is in total lifetime savings — a 10kW system might save $30,000+ more than a 5kW system over 25 years.