Most Cairns homes need between 14 and 24 solar panels. With modern 440 to 470 W panels, a 6.6 kW system is about 15 panels, and a 10 kW system is about 22. The exact number for your house comes down to how much power you use, how much good roof you have, and which panel you pick.
That is the short version. The rest of this guide shows you the simple maths, so you can work out your own number before you talk to anyone.
Quick answer
- Most Cairns homes: 14 to 24 panels
- 5 kW system: about 11 to 12 panels
- 6.6 kW system: about 15 panels
- 10 kW system: about 22 panels
- 13.2 kW system: about 30 panels
- Each panel needs about 2 square metres of roof
We are G-Solar & Electrical, based at 32 Magazine Street in Stratford. Our owner Grant Newman is a fifth generation Cairns electrician, and we size systems for homes from Port Douglas to the Atherton Tablelands every week. Here is how we do it.
How do you work out how many panels you need?
The maths is simpler than most people expect. Three steps.
Step 1. Find your daily usage. Grab your power bill and look for average daily use in kWh. Most bills print it. If yours does not, our Cairns electricity bill guide shows you where to find it and what a normal FNQ number looks like.
Step 2. Divide by 5, then add a margin. Cairns gets about 5 peak sun hours a day. So divide your daily kWh by 5 to get a rough system size in kW. Then add 20 to 30 percent on top. That margin covers the wet season from November to April, when cloud cuts output, plus normal system losses from heat and wiring. Skip the margin and your system will fall short for half the year.
Step 3. Divide by panel wattage. Take your system size in watts and divide by the wattage of one panel. Modern panels are 440 to 470 W. That gives you your panel count.
Here is a worked example. A family uses 25 kWh a day. Divide by 5 and you get 5 kW. Add 25 percent and you get about 6.25 kW, so round up to 6.6 kW. Divide 6,600 W by 440 W and you get 15 panels. Done.
The same maths works anywhere in Australia, you just swap in your local sun hours. Cairns sits at about 5, which is better than most of the country.
How many panels in each system size?
Here is the quick reference for 2026, using 440 to 470 W panels.
| System size | Panels in 2026 (440 to 470 W) | Panels in the old 300 W days | Roof space needed |
|---|---|---|---|
| 5 kW | 11 to 12 | 17 | about 24 m² |
| 6.6 kW | 14 to 15 | 20 to 24 | about 30 m² |
| 10 kW | 21 to 23 | 33 | about 44 m² |
| 13.2 kW | 28 to 30 | 44 | about 60 m² |
Notice how the numbers have dropped. A 6.6 kW system needed 20 to 24 panels when panels were 300 W. Today it needs about 15. Panel counts shrank as wattage rose, which means the same roof now fits a much bigger system than it did five years ago. If your neighbour got quoted 22 panels for a 6.6 kW system back in 2020, that was normal then. It is not normal now.
Most modern residential panels sit in that 440 to 470 W range.
How much roof space do you need?
Each panel takes up about 2 square metres. So a 6.6 kW system needs roughly 30 square metres of good roof, and a 10 kW system needs about 44.
“Good roof” is the key phrase. You need sections that face the right way, do not sit in shade, and can take cyclone rated mounting, because Cairns is in cyclone region C. Most Cairns homes have enough roof, but not always in one clean rectangle. We often split an install across two or three roof faces. If you are not sure what your roof can hold, our tropical roof suitability guide walks through it, and our cyclone proof mounting guide covers how panels stay put in a blow.
What changes the panel count?
Four things move the number up or down.
Roof orientation. North facing roof gives the most total output, so you need the fewest panels. But an east west split works very well in Cairns. East panels catch morning sun while you cool the house down, west panels carry the afternoon load when the air con works hardest. We cover this in detail in our guide to running air conditioning on solar. A south facing roof still works here, we are close enough to the equator, but it produces less, so you may need a panel or two more.
Shading. A shaded panel produces a fraction of its rating. Trees, a neighbour’s second storey, a hot water flue. If part of your roof is shaded for hours a day, we design around it rather than through it, and sometimes that means more panels on the clear sections.
Tilt. Most Cairns roofs sit between 10 and 25 degrees, which is close to ideal for our latitude. Flat roofs need tilt frames, which change spacing and sometimes the count.
Panel wattage. A 470 W panel does the work of one and a bit 440 W panels. Pick higher wattage panels and your count drops. On a tight roof, that matters. Heat also trims output on any panel, which is one reason we add that sizing margin. Our guide to panel efficiency in tropical climates explains how FNQ heat affects real world numbers.
How many panels for your daily usage?
Here are three typical Cairns households, using the maths from above.
A couple using 15 kWh a day. The raw maths says 15 divided by 5 is 3 kW, plus margin, call it 4 kW. But we would still quote 6.6 kW, about 15 panels. The jump in cost from 4 kW to 6.6 kW is small, the STC rebate takes about $1,800 off a 6.6 kW system, and the spare output covers future changes like a battery or a new air con.
A family using 25 to 30 kWh a day. The maths lands between 6.6 and 8 kW once you add the margin. For most of these homes we quote 8 to 10 kW, which is 18 to 22 panels. Families grow into systems fast. Teenagers, a second fridge, more air con hours.
A big house with a pool using 40 plus kWh a day. Pool pumps run for hours and air con runs most of the year. The maths says 10 kW minimum, and we usually quote 13.2 kW, about 30 panels, if the roof allows. You can see systems like this on our recent work.
For a full picture of what each size costs installed, our Cairns solar pricing guide has current ranges. Roughly, a 6.6 kW system runs $5,500 to $8,500 after rebates, and a 10 kW system runs $8,500 to $13,000.
Why we usually size bigger than your bill suggests
If you only match your current bill, you will probably undersize. Here is why we say go bigger in 2026.
The feed-in tariff is small. From 1 July 2026 the feed-in tariff is 6.006 c/kWh. Grid power on Ergon tariff 11 costs roughly 30 to 35 c/kWh. So every kWh you use yourself is worth about five times what you get for exporting it. A bigger system means more of your daily load runs on your own power, morning and afternoon, not just the middle of the day.
Batteries are coming to most homes. A battery soaks up your spare daytime power and gives it back at night. A bigger array fills a battery faster, especially in the wet season. If a battery is on your radar, read our guide on what size solar battery you need before you lock in panel numbers.
EVs change everything. An electric car can add 10 kWh or more to your daily use. Plenty of Cairns families will have one within the life of this system. Our guide to charging your EV with solar shows what that does to sizing.
Adding panels later costs more. A second visit means new mounting, new wiring, sometimes a new inverter, and a fresh install cost on a small job. Doing it once is almost always cheaper per panel. If budget is the worry, we offer payment plans through Handypay so you can size it right the first time.
What about the inverter?
Panel count and inverter size are two different numbers, and that confuses people.
A 6.6 kW array pairs with a 5 kW inverter. That is normal, allowed under the rules, and deliberate. You can oversize an array by up to a third over the inverter rating. The array rarely hits its full paper rating anyway because of heat and cloud, so the oversized array keeps the inverter working near its sweet spot for more hours of the day.
We are a Fronius Partner Plus dealer, and our Fronius inverter guide explains why we back them in FNQ conditions. You can compare the inverters we install on our products page.
FAQ
How many panels in a 10 kW system?
About 21 to 23 panels using modern 440 to 470 W panels. You need roughly 44 square metres of unshaded roof. Five years ago the same system took 33 panels, so counts have dropped a lot.
How many panels for a 6.6 kW system?
About 14 to 15 panels at 440 to 470 W each. It is still the most common size we install on Cairns homes, and it needs about 30 square metres of good roof.
Can I just add more panels later?
You can, but it usually costs more per panel than doing it upfront. Your inverter may not have the headroom, and a small add-on job carries its own callout and install costs. If there is any chance you will want more, size up now.
Is a 5 kW solar system still worth installing?
At about 11 to 12 panels it suits small homes and units with limited roof. But the price gap between 5 kW and 6.6 kW is small, and the rebate helps close it further, so most people are better off going 6.6 kW if the roof fits it.
Get your panel count checked for free
The maths above gets you close. A roof check gets you exact. We look at your bill, your roof faces, your shading and your plans, then give you a panel count and a fixed quote. No pressure, no obligation.
We have 326 Google reviews at a 5.0 rating, and we install across Cairns, the northern beaches, Port Douglas and the Tablelands. Request your free quote here and we will size it properly, once.