Solar system sizes compared
Every size we price, from 5 kW to 20 kW. Prices are after the federal STC rebate in Sydney (zone 3); payback is on bill savings at the middle of each size's bill range.
| Size | Panels | Output a day | Suits a bill of | After STCs | Payback |
|---|---|---|---|---|---|
| 5 kW | 11 on a 5 kW inverter | ~20 kWh | Under $300 | $3,952-$5,652 | 6.0 to 10.5 years |
| 6 kW | 14 on a 5 kW inverter | ~24 kWh | $250-$500 | $4,674-$6,674 | 4.7 to 8.2 years |
| 6.6 kW | 15 on a 5 kW inverter | ~26 kWh | $300-$600 | $5,116-$7,416 | 4.3 to 7.6 years |
| 8 kW | 18 on a 6 kW inverter | ~32 kWh | $500-$800 | $6,219-$8,919 | 3.6 to 6.4 years |
| 10 kW | 23 on a 8.2 kW inverter | ~40 kWh | $700-$1,000 | $7,764-$11,164 | 3.5 to 6.1 years |
| 13.2 kW | 30 on a 10 kW inverter | ~52 kWh | $900+ | $10,292-$14,692 | 4.3 to 7.6 years |
| 15 kW | 34 on a 12 kW inverter | ~60 kWh | $1,000+ | $11,716-$16,816 | 4.4 to 7.8 years |
| 20 kW | 45 on a 15 kW inverter | ~79 kWh | $1,400+ | $15,528-$22,328 | 4.2 to 7.4 years |
Installed band: Per-kW band of $1,050 to $1,390 before rebates: the cheapest (Perth 7 kW) and dearest (Hobart 6 kW) capital-city prices at 6 to 10 kW in the index, Darwin excluded, with each city's STC discount added back. Sizes above 10 kW are scaled at the same per-kW rates; smaller systems usually cost more per kW. Payback assumptions: Sydney (STC zone 3), grid power at 32c/kWh, 1,450 kWh a year per kW, price after the federal rebate only, bill savings only (no VPP income), savings ±10%. General information, not financial advice; the solar cost calculator runs the same numbers for your bill and postcode.
What is the 20% rule for solar?
The "20% rule" is a rule of thumb, not a regulation: size the panels to make about 20% more electricity than you use in a year, to allow for winter, dust and panel ageing. At the 4,333 kWh a year a typical household uses (AER and ESC default offers, 2026-27), that is 5,200 kWh, or about 3.6 kW of panels.
A bigger system often makes sense. Solar alone only offsets what you use while the sun is up, so extra panels cover daytime loads, a battery or an EV, and the price per kW falls as systems get bigger: the Solar Choice Price Index, October 2026 all-cities average after STCs is $1,377 per kW at 3 kW and $981 per kW at 10 kW. The limits that actually bind are the 133% allowance, which lets 6.6 kW of panels run on a 5 kW inverter, and your network's export limit.
How to choose your system size
Three things matter most:
1. Your quarterly electricity bill
Under $300 a quarter: 5 kW. $300-$600 a quarter: 6.6 kW. $500-$800 a quarter: 8 kW. $700-$1,000 a quarter: 10 kW. Bigger bills point to 13.2 kW and up, usually on three-phase power.
2. When you use your power
Households that use most of their electricity during the day (pool pumps, ducted air-con, electric hot water, working from home) get more value from a larger system. Households that use most of their power in the evening should size more conservatively or add a battery.
3. Your future loads
An EV or a heat-pump hot water system adds daytime load you can run from your own panels. If one is coming in the next couple of years, size up a step now rather than adding a second array later.
Is 10 kW solar enough to run a house?
For daytime use, yes for almost every home: a 10 kW system makes about 40 kWh a day against the 11.9 kWh a day a typical household uses. Panels stop at sunset, so the evening needs a battery. The full answer, with payback on two different bills, is in is 10 kW solar enough to run a house.
Common questions
What is the 20% rule for solar?
The "20% rule" is a rule of thumb, not a regulation: size the panels to make about 20% more electricity than you use in a year, to allow for winter, dust and panel ageing. At the 4,333 kWh a year a typical household uses (AER and ESC default offers, 2026-27), that is 5,200 kWh, or about 3.6 kW of panels. A bigger system often makes sense. Solar alone only offsets what you use while the sun is up, so extra panels cover daytime loads, a battery or an EV, and the price per kW falls as systems get bigger: the Solar Choice Price Index, October 2026 all-cities average after STCs is $1,377 per kW at 3 kW and $981 per kW at 10 kW. The limits that actually bind are the 133% allowance, which lets 6.6 kW of panels run on a 5 kW inverter, and your network's export limit.
How do I know what size I need?
Your quarterly bill is the cleanest signal. Under $300 a quarter: 5 kW. $300-$600 a quarter: 6.6 kW. $500-$800 a quarter: 8 kW. $700-$1,000 a quarter: 10 kW. Size up if you have a pool, electric hot water, ducted air-conditioning or an EV coming.
Is 10 kW solar enough to run a house?
For daytime use, yes for almost every home: about 40 kWh a day against the 11.9 kWh a day a typical household uses. Panels stop at sunset, so the evening needs a battery. The full answer is in our guide to whether 10 kW solar is enough.
Does a bigger system always pay back faster?
No. Solar alone can only offset the daytime share of a bill, so a system sized past your bill exports more for a small feed-in tariff. On our calculator a 10 kW system pays back in 3.5 to 6.1 years on the $850 quarterly bill it is sized for, and more slowly on a smaller one.