Quick rule of thumb: Take your quarterly electricity bill, divide by $100 — that's roughly your ideal system size in kW. So a $400/quarter bill → ~4kW minimum, $600/quarter → ~6kW, $900/quarter → ~9kW.
The four most common residential sizes are 5kW, 6.6kW, 10kW, and 13kW. Below we compare them across daily output, annual savings, cost after rebates, payback period, and ideal household type. For a personalised recommendation, use our free solar score calculator. Our rebates guide explains how your STC zone affects the discount for each size.
Quick Comparison
| 5kW | 6.6kW | 10kW | 13kW | |
|---|---|---|---|---|
| Panels | 12–14 | 15–18 | 24–28 | 30–36 |
| Daily Output | 18–23 kWh | 22–30 kWh | 35–45 kWh | 45–58 kWh |
| Cost (after STCs) | $3k–$5k | $3.8k–$6.5k | $5.5k–$10k | $7.5k–$13.5k |
| Annual Savings | $1k–$1.6k | $1.4k–$2.2k | $2k–$3.2k | $2.6k–$4.2k |
| Payback | 3–5 yrs | 3–4.5 yrs | 3–5 yrs | 3–5 yrs |
| Roof Space | ~20 m² | ~26 m² | ~42 m² | ~54 m² |
| Installs | 15% | 45% | 28% | 12% |
5kW
12–14 PANELS · 15% OF INSTALLSView full guide →Choosing the right system size is the single most important decision in your solar journey — it determines your upfront cost, daily output, savings potential, and payback period. A system that's too small won't offset enough of your bill; too large and you're paying for generation you can't use (unless you have a battery or high feed-in tariff). Whether you're considering a 5kW solar, 6.6kW solar, or 10kW solar system, this guide compares every common residential size sold in Australia — solar system sizes compared side by side.For current pricing on each size, see our Solar Panel Cost guide. To understand the rebates that reduce your upfront cost, visit Solar Rebates Australia 2026.Daily Output18–23 kWhCost After STCs$3,000–$5,000Annual Savings$1,000–$1,600Payback3–5 yrsSmall households (1–2 people), smaller roofs, budget entry point6.6kW
15–18 PANELS · 45% OF INSTALLSView full guide →Choosing the right system size is the single most important decision in your solar journey — it determines your upfront cost, daily output, savings potential, and payback period. A system that's too small won't offset enough of your bill; too large and you're paying for generation you can't use (unless you have a battery or high feed-in tariff). Whether you're considering a 5kW solar, 6.6kW solar, or 10kW solar system, this guide compares every common residential size sold in Australia — solar system sizes compared side by side.For current pricing on each size, see our Solar Panel Cost guide. To understand the rebates that reduce your upfront cost, visit Solar Rebates Australia 2026.Daily Output22–30 kWhCost After STCs$3,800–$6,500Annual Savings$1,400–$2,200Payback3–4.5 yrsAverage households (2–4 people) — Australia's most popular size10kW
24–28 PANELS · 28% OF INSTALLSView full guide →Choosing the right system size is the single most important decision in your solar journey — it determines your upfront cost, daily output, savings potential, and payback period. A system that's too small won't offset enough of your bill; too large and you're paying for generation you can't use (unless you have a battery or high feed-in tariff). Whether you're considering a 5kW solar, 6.6kW solar, or 10kW solar system, this guide compares every common residential size sold in Australia — solar system sizes compared side by side.For current pricing on each size, see our Solar Panel Cost guide. To understand the rebates that reduce your upfront cost, visit Solar Rebates Australia 2026.Daily Output35–45 kWhCost After STCs$5,500–$10,000Annual Savings$2,000–$3,200Payback3–5 yrsLarge households, home offices, pools, future EV charging13kW
30–36 PANELS · 12% OF INSTALLSView full guide →Choosing the right system size is the single most important decision in your solar journey — it determines your upfront cost, daily output, savings potential, and payback period. A system that's too small won't offset enough of your bill; too large and you're paying for generation you can't use (unless you have a battery or high feed-in tariff). Whether you're considering a 5kW solar, 6.6kW solar, or 10kW solar system, this guide compares every common residential size sold in Australia — solar system sizes compared side by side.For current pricing on each size, see our Solar Panel Cost guide. To understand the rebates that reduce your upfront cost, visit Solar Rebates Australia 2026.Daily Output45–58 kWhCost After STCs$7,500–$13,500Annual Savings$2,600–$4,200Payback3–5 yrsHigh-usage homes, all-electric properties, EV ownersWhat Determines Your Ideal Size?
The right system size depends on several factors unique to your home. Here's what matters most and how each one affects your recommendation.
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.
Common Sizing Mistakes
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.
Solar By Location
Related Guides
System Size FAQ
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.
Not sure which size is right? Our scorecard analyses your bill, roof, and location to recommend the ideal system.