Most Sydney homes we look at land somewhere between a 6.6kW and a 13.2kW solar system, costing roughly $5,500 to $11,000 after the federal STC rebate. The right number for you comes down to three things: how much power you use, when you use it, and how much roof you've got facing the right way.

Sizing a system isn't guesswork, and it isn't about cramming on as many panels as possible. Get it wrong and you either run short on the days you need power most, or you export cheap electricity to the grid for 4-7c/kWh while still buying it back at 35c. Here's how we work it out.

Start with your actual usage, not a sales target

Pull out your last four quarterly bills. Look for your average daily usage in kWh — it's printed on every Ausgrid and Endeavour bill, usually as a little bar graph. A typical Sydney household sits between 16 and 25kWh per day, but families in Frenchs Forest with ducted air-con and a pool can push past 40kWh.

As a rough rule, each kW of north-facing solar produces about 4kWh per day across the year in NSW. So a 6.6kW system makes roughly 26kWh on a good day and far less in a wet July week. We size to cover your daytime load plus a sensible buffer, not your total annual usage on paper.

The bit that matters most: when you use power

Solar only offsets what you use while the sun's up, unless you add a battery. If both of you work full-time and the house is empty until 6pm, a giant system mostly exports power for almost nothing. That's the most common mistake we see — an oversized array bought on the promise of a feed-in tariff that's been falling for years.

If you can shift your dishwasher, washing machine, pool pump and hot water to the middle of the day, a bigger system pays off. If you can't, the smarter play is often a battery to store the surplus for the evening peak. The NSW battery incentive (under the PDRS) currently knocks a few thousand dollars off an installed battery, which changes the maths considerably.

Roof space, orientation and shade

A 6.6kW system needs around 16-18 panels and roughly 30 square metres of clear roof. North is best, but east-west splits work well too — they spread generation across morning and afternoon, which often suits real household patterns better than a single north run.

Shade is the quiet killer. A single tree branch or a chimney shadow crossing the array at 4pm can drag down a whole string. On the quote visit we check this with the actual sun path, not just by eyeballing the roof on a clear morning. In leafy pockets of Mona Vale and Dee Why we'll often recommend microinverters or optimisers so one shaded panel doesn't pull the rest down.

The switchboard and metering gotchas

Here's something only a sparky flags before you sign anything: your switchboard and your network connection limits the system you can install. Endeavour and Ausgrid cap how much you can export on a standard single-phase connection — commonly 5kW of inverter export. You can still install a larger array, but it may need export limiting or an upgrade to three-phase.

We also check whether your switchboard has room for a solar breaker and whether it has surge protection and a main switch that meets current standards. Older boards in homes around Charlestown often need a small upgrade before solar can be safely connected — budget $500-$1,500 if that's the case. Your existing meter also has to be reconfigured or replaced by the retailer to record export, which we coordinate so you're not left buying power you're actually generating.

A practical sizing example

Take a Northern Beaches family using 22kWh a day, mostly mornings and evenings, with a north-east roof and partial afternoon shade. We'd typically recommend a 10kW array on optimisers paired with a battery to catch the daytime surplus for the evening peak.

For a retired couple in Newcastle home all day, using 15kWh and able to run appliances at noon, a straightforward 6.6kW system with no battery often gives the best return — because they self-consume nearly everything they make. Same suburb, same roof, completely different answer.

Get a sizing that fits your actual house

The honest answer is that the right system size depends on your bills, your daily routine, your roof and your switchboard — not a number off a flyer. We'd rather spend twenty minutes getting that right than sell you panels you'll never fully use.

If you'd like a straight, no-pressure assessment, send us a recent power bill and book a free site visit. We'll check your roof, your board and your network limits, and give you a system size and price that actually stacks up for your home.