Start with the bill, not the roof
Every cold-call quote starts with your roof: how many panels fit. Every good design starts with your bills: how much power you actually use, and when. Grab a recent bill and find your average daily usage in kWh — for most Melbourne family homes it sits somewhere between 12 and 25kWh a day, higher with a pool, ducted heating or an EV.
The Melbourne maths
A well-positioned north-facing panel in Melbourne produces roughly 3.6kWh per kW of capacity per day averaged across the year — more in January, less in July. So a 6.6kW system averages around 24kWh a day; a 13.2kW system around 48. But averages hide the shape: winter output can drop to half the yearly average exactly when a heat pump and electric heating push usage up. Sizing to your annual average leaves you short in the months that matter most.
roughly the kWh each kW of well-placed solar produces per day in Melbourne, averaged across the year.
Why bigger is usually (but not always) right
Panels are the cheap part of a solar job — the scaffolding, the crew, the inverter and the paperwork cost the same whether the roof carries 6.6kW or 10kW. That's why filling the good roof space usually pays: the extra capacity costs little and future-proofs you for a battery, an EV or getting off gas. The exceptions are real, though: heavy shading, a small or badly-oriented roof, or a single-phase connection that caps your export. This is exactly the stuff an assessment checks before anyone orders hardware.
Panels are the cheap part. If the roof is good, filling it usually costs less per kilowatt — not more.
The questions that change the answer
Are you home during the day, or does the house sit empty until 6pm? (Daytime users self-consume more; commuter households lean harder on a battery.) Is an EV coming in the next five years? Is the gas hot water or heating on its way out? Each yes pushes the right size up a bracket, because the cheapest time to add capacity is while the crew is already on the roof.
How to sanity-check any quote
Ask three things. One: what daily usage did you size this from? If they never asked for your bills, it's a template. Two: what does the winter production look like, month by month? A real design has monthly modelling, not an annual average. Three: what happens when I add a battery or an EV charger later? The answer should be specific — inverter compatibility, phase, switchboard capacity — not a shrug.
Want this worked out for your place?
A real electrician, at your kitchen bench, with the numbers for your roof and your bills.
- Size from your bills and their timing — never from the postcode.
- Melbourne solar averages ~3.6kWh per kW per day, but winter halves it.
- If the roof is good, fill it — panels are the cheap part of the job.
- Any quote without your usage data and monthly modelling is a template.
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Written by Luke Jones, A-Grade electrician (REC 33326)
Luke runs Polarised Electrical out of Boronia. Everything here comes from jobs we've done across Melbourne's east — not a brochure.
