Solar guide
What size solar system do I need?
The right size depends on how much power you use, when you use it, whether a battery or an electric car is in your plans, and what your roof and your connection allow.
Work it out in four steps
Step 1: Find your daily use
Your bill shows how many kWh you use per day or per quarter (divide a quarter by about 91). Use a year of bills if you can, because summer and winter differ.
Step 2: Think about when you use it
Solar covers daytime use directly. If most of your use is in the evening, a bigger system on its own helps less, unless you add a battery or move some use to the middle of the day.
Step 3: Add what's coming
A battery, an electric car, a pool or a move to electric heating and cooking all add to the system you'll want. Sizing for them now can be simpler than adding panels later.
Step 4: Check what your roof and connection allow
Usable roof space, shading, and your network's inverter and export limits set the ceiling. Installers check these when they quote.
What each size produces
Average daily output from the Clean Energy Regulator's rating for zone 3, which covers South East Queensland and Sydney (3.8 kWh per kW per day across the year). Real output is usually a little lower after shading, roof direction and losses, and summer days produce more than winter days. Panel and roof figures assume 440 W panels of about 2 m² each.
- 6.6 kW: around 25 kWh a day on average, about 15 panels and 30 m² of roof
- 10 kW: around 38 kWh a day on average, about 23 panels and 46 m² of roof
- 13.2 kW: around 50 kWh a day on average, about 30 panels and 60 m² of roof
- 15 kW: around 57 kWh a day on average, about 35 panels and 70 m² of roof
- 20 kW: around 76 kWh a day on average, about 46 panels and 92 m² of roof
Why 6.6 kW and 13.2 kW are such common sizes
For a system to earn small-scale technology certificates (the federal solar discount), the panels can be up to a third bigger than the inverter. So 6.6 kW of panels pairs with a 5 kW inverter, and about 13.3 kW pairs with a 10 kW inverter.
Panels produce below their rating most of the day, so a slightly smaller inverter rarely loses much output, and the inverter is often the part network limits apply to.
Network limits: single-phase and three-phase homes
Most homes have single-phase power. In South East Queensland, Energex's standard connection allows up to 10 kVA of inverter capacity and up to 5 kW of exports per phase, and a battery's inverter counts towards that limit. That makes about 13.2 kW of panels on a 10 kW inverter the practical maximum for most single-phase homes there. Other networks set their own limits, so check yours.
15 kW and 20 kW systems usually need three-phase power. Energex also offers dynamic connections, which can allow higher exports when the grid has room. New and replacement systems of 10 kVA or more in Queensland need an emergency backstop device.
A bigger system than you can export isn't wasted if you can use the extra during the day, store it in a battery or charge a car with it.
Ask each installer
- What size they recommend and how they worked it out from your usage
- How many panels, which model, and where on the roof they'll go
- The inverter size and whether it can take a battery later
- Whether your supply is single- or three-phase, and what export limit applies
- Expected output for your roof's direction and any shading
Sources
Facts on this page were checked on 15 October 2026. Rules and programs change, so confirm details with your installer.
- Clean Energy Regulator — Postcode zone ratings and zones for solar panel systems
- Solar Victoria — Finding the right inverter for your system
- Energex — Model standing offer: basic micro embedded generating units (0–30 kVA)
- Energex — Dynamic connections: homeowners and small business
- Queensland Treasury — Emergency backstop mechanism
Frequently asked questions
Is a 6.6 kW system big enough?
It suits many smaller households, particularly those home during the day. If you use a lot of power in the evening, plan a battery, or drive an electric car, a larger system is often worth comparing.
Can I put 20 kW of solar on a single-phase home?
Generally not on a standard connection in South East Queensland, where inverter capacity is limited to 10 kVA per phase. Ask installers whether three-phase power or a dynamic connection is an option for your home.
Should I get a bigger system now if I'm adding a battery later?
Often, yes. A battery needs spare solar to fill it. The battery size guide shows roughly how much.
Get quotes sized for your home
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