How Much Solar Do I Actually Need?
Why the 6.6 kW default is usually wrong and how to size a system for the home you'll have in 5 years.
The default 6.6 kW system became standard in Australia because it was the largest array a 5 kW inverter could legally pair with. That math hasn't been relevant for years. With cheap panels, larger inverters and Flexible Exports, the right system size for most SA homes today is 10-15 kW — sometimes more.
Start with consumption, not roof space
Pull 12 months of bills. Average daily kWh is the headline number. A typical SA family home runs 18-30 kWh/day; add 10-15 kWh/day per EV, 5-10 kWh/day per pool, and 8-12 kWh/day if you have ducted reverse-cycle running through summer.
Rule of thumb: design solar to produce 1.5-2× your current daily consumption. That gives headroom for an EV, a battery, a heat pump and the loads you'll add over the next 5 years without re-quoting the array.
Why bigger is usually right
Panels are now the cheapest component per watt. Stepping up from a 6.6 kW system to 10 kW is usually a relatively small uplift on the overall quote but produces around 50% more energy — far more useful in a battery + EV future. Every job is priced on its own specifics.
Inverter sizing matters: aim for a DC:AC ratio of 1.2-1.33. That gives you more morning and afternoon production and is the standard CEC-accepted design.
Three-phase, single-phase, export limits
Most SA homes are single-phase, which caps inverter export at 5 kW under standard connection rules (or 10 kW with Flexible Exports and a smart inverter). Three-phase homes can export 15 kW. If you're on three-phase, a 15 kW system is almost always the right starting point.
Battery + Flexible Exports lets you build a 13-20 kW array on single-phase by self-consuming the surplus into the battery during peak production.
Key takeaways
- Size to 1.5-2× current daily consumption.
- Most SA homes today are best served by 10-15 kW.
- Three-phase + Flexible Exports unlocks bigger systems without wasted production.
Sources & further reading
- SolarQuotes — sizing guides
- Clean Energy Council — design guidelines
- SA Power Networks — connection limits
This article is general information only. Figures change with policy, tariffs and product pricing — for a current quote tailored to your home, start an assessment or contact our team.