What a 20kW solar system costs in Perth (October 2026)
Installed and GST inclusive with Tier 1 panels and a quality string inverter, a 20kW system in Perth is $11,850–$16,980 after the federal STC discount of $5,507 (STC Zone 3). That is $17,357–$22,487 before the discount, which the installer takes off the quote.
| Tier | Installed after STCs | Per watt |
|---|---|---|
| Budget | $9,779–$14,013 | $0.59/W |
| Mid-range (most quotes) | $11,850–$16,980 | $0.72/W |
| Premium | $15,532–$22,255 | $0.94/W |
Perth runs about 21% below the national average for this size. Full breakdown by size and tier on the Perth solar cost page.
How much a 20kW system generates in Perth
With 5.4 peak sun hours a day, 45 panels (20kW) in Perth produce about 30,747 kWh a year — roughly 84 kWh a day averaged across the year, more in summer and less in winter.
Using about 40% of that on site at 33c/kWh and exporting the rest at 2.8c saves $4,110–$5,710 a year, for a payback of 2.5–3.5 yrs. Shift the dishwasher, washing machine and hot water into daylight hours and you land at the short end.
Is 20kW the right size for your Perth home?
20kW suits very large homes, home businesses, farms and small commercial premises — usually three-phase. As a rule of thumb it matches a quarterly electricity bill of $1,600+ or daily use of 55+ kWh.
- Roof space: about 90m² of unshaded roof for 45 × 440W panels, ideally north, or split east/west
- Inverter: three-phase inverter, usually 15–17kW
- Export limits: most WA networks cap single-phase export at 5kW — ask about export limiting or three-phase, or add a battery to soak up the surplus
- Going bigger: cost per kW falls with size, so if the roof allows, a commercial-scale system is often only a little more per month on finance
Not sure? The free Perth solar score sizes the system from your bill and household.
20kW solar with a battery in Perth
A 20kW array pairs naturally with a 13.5kWh battery. Adding one costs $8,603–$11,603 after the federal battery discount of $3,397, and shifts about 10 kWh of solar into the evening each day — worth roughly $1,192 a year at Perth tariffs. Solar and battery as one job in Perth: $20,453–$28,583.
Brand-by-brand installed prices are in the battery guide.
Rebates on a 20kW system in WA
- Federal STC discount: $5,507 on 20kW in Zone 3 (20 kW × 1.382 × 5 years × $39.85). Deeming drops to 4 years on 1 January 2027, cutting this by about $1,101.
- WA: the WA Residential Battery Scheme (Synergy up to $1,300, Horizon up to $3,800, VPP required) plus an interest-free loan up to $10,000.
- Battery: $252 per usable kWh under the federal Cheaper Home Batteries program.
Other sizes in Perth and 20kW elsewhere
Other sizes in Perth
20kW in other cities
20kW in Perth: common questions
How much does a 20kW solar system cost in Perth?
$11,850–$16,980 installed after the $5,507 federal STC discount, for Tier 1 panels and a quality inverter (October 2026). Premium panels with micro-inverters run to about $22,255.
How many panels is a 20kW system?
45 panels at today's 440W size, needing about 90m² of roof. Older 370–400W panels would mean 52.
How much power does 20kW produce in Perth?
About 30,747 kWh a year — 112 kWh a day in the best month and 56 in the worst — on an unshaded north-facing roof.
What is the payback on a 20kW system in Perth?
2.5–3.5 yrs, saving $4,110–$5,710 a year at 33c/kWh. A battery lengthens payback slightly but lifts the saving.
Get 20kW quotes in Perth
The free solar score checks whether 20kW is the right size for your bill and roof, shows the Perth price range, and — only if you ask — shares your enquiry with up to two CEC-accredited local installers. Get my solar score →