What size solar system does a Perth home need?
A plain guide to sizing solar for a Perth home: how to read your bill, when 6.6kW, 10kW or 13kW makes sense, and why battery plans change the answer.
“How big should my system be?” is the first question almost every customer asks. The honest answer is that it depends on how much power you use, when you use it, and what you plan to add in the next few years. Here is how we work it out.
Start with your bill, not the panel count
Your Synergy bill shows your average daily usage in kWh. As a rough guide, each kilowatt of panels on a well-oriented Perth roof produces around 4 to 4.5kWh per day averaged across the year, more in summer and less in winter. A home using 20kWh a day is a very different case from one using 40kWh.
Just as important is when you use that power. Solar only produces during the day. If most of your usage is after 5pm, a bigger solar system without a battery will mostly export to the grid, and Synergy pays far less for exported power than you pay to buy it back.
A simple starting point
| System | Usually suits |
|---|---|
| 6.6kW | Smaller households, or homes using most power during the day |
| 10.2kW | Families with daytime and evening usage, or planning a battery |
| 13.2kW | Larger homes, pools, ducted air conditioning, EVs or three-phase properties |
These match the standard packages on our Solar & Batteries page, but every system is checked against your roof and switchboard before we quote.
What else changes the answer
- A battery. If you want a battery now or later, you need enough solar to run the house during the day and charge the battery. That usually pushes the system size up.
- An EV. An electric car driving 15,000km a year can add around 7 to 8kWh a day. Charging at home on solar is the cheapest way to run one.
- Single or three phase. Western Power sets limits on inverter size and export for each connection type. We check what your property is allowed during the design and handle the application.
- Roof space and shading. East and west roofs work well in Perth and spread production across the day. Shade from trees or a neighbour’s second storey can change the layout entirely.
Bigger isn’t always better
A system that is too big for your usage and export limits will look good on paper but pay back slowly. A system that is too small leaves no room for a battery or EV later. We design for how you use power now and what you have planned, and we’ll show you the numbers both ways if you’re unsure.
Common questions
How many panels is a 6.6kW system?
With 440W panels, a 6.6kW system is 15 panels. A 10.2kW system is around 23 panels and a 13.2kW system is 30.
Can I add more panels later?
Sometimes, but it depends on your inverter, roof space and Western Power approval. It is usually cheaper to size correctly the first time.
Do I need a three-phase connection for a big system?
Not always, but three-phase properties generally have higher inverter and export allowances. We check this during the design.
