Commercial solar by size
100 kW solar system: cost, output and payback (2026)
100 kW at a glance
- Panels
- about 228
- at 440 W each (assumed)
- Panel area
- about 502 m²
- at 2.2 m² a panel, before access paths
- Output
- 119 to 154 MWh a year
- across the eight capital cities
- Certificates
- small-scale STCs
- declining each year to 2030
What does a 100 kW system cost?
| City | Average price |
|---|---|
| Sydney | $88,850 |
| Melbourne | $77,310 |
| Brisbane | $85,170 |
| Adelaide | $83,900 |
| Perth | $83,410 |
| Hobart | $70,730 |
| Canberra | $81,650 |
| Average of all cities | $81,570 |
Solar Choice has no Darwin figure. Most GST-registered businesses claim GST back, so divide by 1.1 for a rough ex-GST price. Quotes vary a lot with the roof, the network and the installer.
How much does 100 kW make in each capital?
| City | Postcode | Zone (rating) | kWh a year | Certificates |
|---|---|---|---|---|
| Sydney | 2000 | 3 (1.382) | 138,200 | 691 |
| Melbourne | 3000 | 4 (1.185) | 118,500 | 592 |
| Brisbane | 4000 | 3 (1.382) | 138,200 | 691 |
| Adelaide | 5000 | 3 (1.382) | 138,200 | 691 |
| Perth | 6000 | 3 (1.382) | 138,200 | 691 |
| Hobart | 7000 | 4 (1.185) | 118,500 | 592 |
| Canberra | 2600 | 3 (1.382) | 138,200 | 691 |
| Darwin | 0800 | 2 (1.536) | 153,600 | 768 |
Certificates assume installation on 1 November 2026. Rating in MWh per kW per year.
Panels and roof
- You need more roof than the panel area: walkways for maintenance, setbacks from edges, and gaps between rows if the panels are tilted on a flat roof.
- The roof must carry the load. Older or sheet-metal roofs may need a structural engineer’s report, and asbestos roofs are a separate problem to solve first.
- Your installer’s panel size will differ from our assumption, so the panel count will too. Ask for the layout drawing.
Which certificates does it get, and why?
It earns small-scale STCs: size × zone rating × deeming years, rounded down. The deeming period is the number of years left until the scheme ends in 2030: 5 for 2026, 4 for 2027, 3 for 2028, 2 for 2029 and 1 for 2030. So waiting a year costs about 139 certificates in zone 3, roughly $4,865 at $35 each.
Try your own postcode and date in the STC calculator, and read our guide to commercial solar rebates.
Network approval
Systems over about 30 kW usually need the local network’s approval before they are switched on, and sometimes studies, protection equipment or limits on how much you can export. That can add cost and weeks or months.
Start the application early, and ask each installer who pays for studies and what happens if the network says no. Read our guide to grid connection.
A worked payback example
- Output in year 1
- 138,200 kWh
- Used on site (modelled)
- 75%
- Saving in year 1
- $26,966
- Installed price
- $105,000 excluding GST
- Certificates (small-scale STCs)
- 691 worth $24,185
- Net cost
- $80,815
- Simple payback
- 3.1 years
- 25-year NPV at 7%
- $274,620
- IRR
- 33.7%
- Cost per kWh over its life
- 6.4c
Assumptions in this example
- Electricity rate avoided: 25 c/kWh excluding GST, rising 2.5% a year.
- Export rate: 3 c/kWh, held flat.
- Installed price: $1,050 per kW before certificates, excluding GST.
- Certificates at $35 each; installed 1 November 2026.
- Output falls 0.5% a year; maintenance $12 per kW a year, rising with prices; 25 years.
- Discount rate 7%.
- Not included: demand charges, batteries, finance costs, tax and depreciation, network costs, inverter replacement.
Questions about 100 kW systems
- How much does a 100 kW commercial solar system cost?
- Solar Choice, a comparison site, put the average installed price of a 100 kW system at $81,570 across Australian cities in September 2026, after STCs and including GST. It excludes metering, ground-mounting, grid protection and connection studies, so quotes can be higher.
- How much electricity does a 100 kW system make?
- About 118,500 to 153,600 kWh a year, depending on the city, using the Clean Energy Regulator’s zone ratings (size × rating × 1,000). In Sydney that is 138,200 kWh. Real output varies with shade, tilt, orientation and dirt.
- Does a 100 kW system get the solar rebate?
- Yes. Systems up to 100 kW earn small-scale STCs: size × zone rating × the years left until 2030. Installed in 2026 that is 5 years, so about 691 certificates in Sydney, worth roughly $24,185 at $35 each.
- How many panels and how much roof does 100 kW need?
- About 228 panels at 440 W each, covering roughly 502 square metres of panel area. You need more roof than that for access paths, edge setbacks and tilt-frame spacing, and the roof must be strong enough and not heavily shaded.
- Is a 100 kW system the right size for my business?
- It often suits a factory, a supermarket, a school or a mid-sized warehouse. The right size depends on how much power you use in daylight, not how much roof you have. The usual mistake is a system bigger than your daytime use, which exports surplus at a low rate. Run your numbers in the calculator.
- When is solar not worth it for a business?
- When you rent with a short lease, plan to move, mostly use power at night, have a shaded, fragile or asbestos roof, or can’t get the network’s approval to connect. In those cases, ask about energy efficiency first, or a lease with the landlord’s agreement.
Sources
- Solar Choice: commercial solar pricing (September 2026)
- Clean Energy Regulator: transitional guidance for mid-scale solar (PV) systems
- Clean Energy Regulator: postcode zone ratings
- Clean Energy Regulator: deeming period decline
- Clean Energy Regulator: large-scale generation certificates
Checked 31 October 2026. This page is general information, not financial, tax or legal advice. Rules, rebates and prices change, so check the sources before you decide.
Ready to compare real numbers?
Run your own figures first, then ask at least three accredited installers to quote on the same brief. Quotes are free and you’re under no obligation.