How to Choose the Right Solar System Size (Not the Biggest)

Every solar quote seems to nudge you toward a larger system. More panels, more kilowatts, a bigger number on the invoice. But the system that pays back fastest is rarely the biggest one — it's the one matched to how and when you actually use electricity. This guide walks through the sizing logic we use in an audit, so you can judge a quote on your own terms.

Why bigger isn't automatically better

Solar only saves you money two ways: by offsetting power you'd otherwise buy from the grid, and by exporting the surplus for a feed-in tariff (FiT). The first is worth a lot — you avoid the full retail rate. The second is worth very little. Across Australia, feed-in tariffs typically sit in the range of 3–10 c/kWh, and they've trended down for years. In most states the rate is retailer-set; Victoria, regional Queensland and Tasmania set a regulated minimum, so confirm the current figure for your state.

That gap changes everything. Every kilowatt-hour you consume from your own panels might save you 30-something cents. Every kilowatt-hour you export might earn you a fraction of that. An oversized system pumps more and more energy into low-value exports — so its extra cost takes longer to earn back.

Start with your actual usage, not the roof

Pull out a recent bill (ideally a full year, to capture summer and winter). You want two things: your annual kWh, and when that energy is used. A smart meter gives you half-hourly data — gold for this.

As a rule of thumb nationally, each kilowatt of panels produces roughly 1,400 kWh per year (this varies with location, orientation and shading). So a 6.6 kW system generates in the order of 9,000 kWh a year. The question isn't whether you can generate that — it's how much of it you'll be home to use.

• Out all day, no battery? You'll self-consume less, so a very large array mostly exports cheaply. A modest system often pays back faster.
• Home during the day, or run pool pumps, aircon, EV charging in daylight? You can soak up more of the generation, which justifies more kW.
• Thinking about a battery or an EV later? That shifts the maths toward a larger array — but size for the plan you'll actually act on, not a maybe.

Export limits and the 6.6 kW sweet spot

There's a physical ceiling too. Many single-phase connections cap export at 5 kW. A common, cost-effective setup is around 6.6 kW of panels on a 5 kW inverter — it over-panels slightly to lift winter and shoulder-hour output while staying within export rules. If you want to go bigger, you may need three-phase supply or distributor approval, which adds cost and admin.

Indicative installed prices (after federal STCs, which are already baked into these figures) give a sense of scale:

System size	Typical price after STCs
6.6 kW	$4,000 – $6,500
10 kW	$6,000 – $10,000
13.2 kW	$7,500 – $13,000

Notice the cost rises steadily, but — if you can't self-consume the extra — the savings don't rise in step. That's the trap of buying size for its own sake.

Shift your usage before you buy more panels

Before upsizing, see if you can move load into daylight. Running the dishwasher, washing machine, pool pump or EV charger between late morning and mid-afternoon converts low-value exports into high-value self-consumption — for free. Some retailers also offer the federal Solar Sharer free-power window (live from 1 July 2026), typically 11am–2pm with a daily cap around 24 kWh, on an eligible plan with a smart meter. Availability varies by retailer and state, so confirm what's offered to you. The point: good habits can beat extra kilowatts.

Here's the catch — a bigger system can pay back slower

It's entirely possible for a 13.2 kW system to save you less per dollar spent than a 6.6 kW one. If you're exporting most of the extra generation at single-digit feed-in rates, those additional panels earn back slowly. A larger system isn't "wrong" — it can make sense if you have high daytime use, a battery, or an EV — but it has to be justified by consumption, not by the quote looking impressive. Ask any installer to show you the self-consumption assumption behind their savings estimate. If they can't, treat the payback number with caution.

And for some households, after you've looked at the numbers honestly, a smaller system — or waiting until you add a battery or EV — is the better financial call. That's a legitimate outcome, not a failure.

We don't sell or install panels, and we don't earn a cent on system size. We charge one fixed fee to model your actual usage and tell you the kW that pays back fastest for you — even if that's smaller than every quote in your inbox, or no change at all.

Figures in this guide are current at the date of publication and indicative only — rebate and certificate values change over time (federal battery certificates step down each January and July), and state schemes are amended often. Confirm the current numbers for your situation before you commit. This is general information, not personal financial advice.