Most solar quotes are not designed for your home. They are designed for your roof. That one distinction is the source of most underperforming solar systems in Australia. This guide gives you the specific questions to ask and the numbers to check before you sign anything.
Key findings
- A quote that doesn't start with your kWh (kilowatt-hour) consumption figure was not designed for your household. A kilowatt-hour is the unit of electricity on your bill.
- The most common sizing method in the industry is available roof space. It produces the wrong answer for most homes.
- A well-designed quote will show you the specific daily kWh figure it was built around. Ask for it.
- System size and savings projections are meaningless without this number.
- You can get the right number yourself in under two minutes from your electricity bill.
Why most quotes are wrong before they start
When an installer comes to your home, the first thing they look at is your roof. How many panels can we fit? Which way does it face? Is there shading? These are real considerations, but they're the second conversation, not the first.
The first question should be: how much electricity does this household actually use? Not the average Australian household. Not a four-bedroom home. This household, based on twelve months of real bills.
The number that tells you everything
Find your average daily consumption in kWh on your bill. Then ask your installer: what daily kWh figure did you use to size this system? If they can't answer that question immediately, the system was not designed for your household.
What a well-designed quote looks like
A quote from an installer who has actually designed your system, rather than sized it for your roof, will contain specific information that a lazy quote won't. Here's what to look for.
| What to check | Red flag if… |
|---|---|
| Daily kWh consumption figure used in design | It's missing, or it's a round number like "20kWh" with no explanation |
| System size justified against your usage | Size described as what "fits your roof" or "maximises your rebate" |
| Annual generation estimate in kWh | Only a percentage saving quoted, with no absolute kWh figure |
| Savings projection with assumptions shown | Savings quoted without stating the assumed feed-in tariff or usage split |
| Panel and inverter specifications | Generic descriptions without brand, model, and warranty terms |
| Future usage considered (EV, pool, etc.) | No questions were asked about planned changes to your household |
The questions most people don't think to ask
"What feed-in tariff did you use to calculate my savings?"
Most savings projections assume a feed-in tariff. If an installer assumed 10¢ but yours is 5¢, your real savings will be lower. Ask what rate they used.
"Is my inverter battery-compatible?"
If you're not adding a battery now but might later, this matters. Some inverters cannot be retrofitted for battery storage. Ask before you sign, not after.
"Who do I call at year five if something goes wrong?"
A good installer will have a direct answer: a named service team, a documented process, and clarity on whether the warranty is backed by the installer, the manufacturer, or a third party. Vagueness here is a red flag.
Sources
- Clean Energy Regulator, STCs guide for householders · cleanenergyregulator.gov.au
- Australian Energy Market Commission, retail energy market report · aemc.gov.au
- Australian Government, Solar for households, energy.gov.au · energy.gov.au