Solar design
What size solar system do I actually need?
How to choose a solar system size in Australia using usage, roof space, tariffs, export limits, batteries and future loads.
Short answer
The right solar system size is driven by your usage pattern, roof, tariff, export limits and future loads, not just by how many panels fit. The aim is to maximise valuable self-consumption while leaving a sensible pathway for batteries, EVs or electrification later.
Start a quoteStart with usage, not roof space
A roof can often fit more panels than the household can use well. That does not make the largest possible system the right system.
Start with recent electricity bills, interval data if available, weekday and weekend usage, and whether major loads happen during the day or after sunset.
Daytime load is the first design lever
Solar is most valuable when the home uses it directly. If the household can run pool pumps, hot water, dishwashers, laundry, air conditioning or EV charging during daylight, a larger system can make more sense.
If nobody is home and flexible loads are limited, a smaller system or battery-ready design may produce better economics.
Check export limits and tariff assumptions
Many networks and retailers limit how much solar can be exported, and feed-in rates are often lower than import rates. A quote that assumes unlimited, high-value export can mislead.
The quote should show assumed export, self-consumption, feed-in tariff, import rate and any time-of-use assumptions.
Plan for future loads
A system sized only for today can feel small once the household adds an EV, heat pump hot water, induction cooking, pool heating or a battery.
That does not mean oversizing blindly. It means designing the inverter, roof layout and switchboard path with realistic future changes in mind.
Use STCs correctly in the comparison
Federal STCs reduce the upfront cost of eligible solar, but the value depends on system size, location, certificate price and timing.
A bigger system can receive more certificate value, but that is not a reason to buy extra capacity if the household will mostly export low-value energy.
Sources
Primary references used for this guide.
Rebate settings and certificate values change. Use these sources for live program rules before accepting a quote.
FAQ
Is a 6.6 kW solar system enough?
It can be enough for some homes and too small for others. The answer depends on usage, roof orientation, export limits, tariff and future loads.
Should I fill my roof with panels?
Only if the design and economics support it. More panels can help, but not when most extra generation is low-value export or the quote ignores site constraints.
Should I size solar differently if I want a battery later?
Yes. Battery-ready design should consider evening load, excess daytime solar, inverter compatibility and how the battery will be charged.
Related guides
Keep reading.
Solar economics
Is solar worth it in Australia in 2026?
For most Australian homes, yes. A well-designed solar system typically pays for itself in three to six years, and every year after that is money saved. But whether solar is worth it depends less on system size than on how much of its power you use yourself.
Solar economics
Solar feed-in tariffs in 2026: why self-consumption matters
A solar feed-in tariff is the rate your retailer pays for excess solar sent to the grid. In 2026, the useful money is usually not in exporting more; it is in using more solar inside the home because exported solar is often worth much less than electricity bought back later.
Solar rebates
Solar rebate stacking: federal and state incentives explained
Solar rebate stacking means combining federal support, such as solar STCs or the Cheaper Home Batteries Program, with a state or territory incentive. It can work, but every layer has its own rules, so the quote must itemise each incentive and confirm that one program does not block another.