"Pays for itself in three years." It's the line that sells more solar systems than any other — and in 2026, it deserves more scrutiny than ever. Payback periods aren't facts; they're forecasts built on assumptions. Two installers quoting the same roof can land years apart simply by tweaking the inputs.
Here's how to pull those numbers apart before you sign anything.
The four assumptions behind every payback claim
1. Your usage profile and self-consumption rate
The single biggest lever in any payback calculation is how much of your solar power you actually use yourself. Every kilowatt-hour you self-consume replaces grid power at full retail rates; every one you export earns far less — sometimes nothing.
If a quote assumes you'll self-consume 50–60% of your generation but you're out of the house all day, the real figure could be closer to 20–30%. Ask each installer what self-consumption rate they've assumed and why. If they haven't asked about your daytime habits, that's a red flag.
2. The electricity tariff — including the 2026–27 DMO cut
Savings estimates hinge on the price you'd otherwise pay for grid power. The AER's final Default Market Offer for 2026–27, released on 26 May 2026, cut residential prices in most regions from 1 July — South East Queensland fell the most, while South Australia edged slightly up. Smart meter households on time-of-use standing offers saw reductions across all three DMO regions.
Lower grid prices modestly stretch payback periods, so a quote built on last year's tariffs (or an inflated "average" rate) will look rosier than reality. Ask which tariff, in cents per kWh, sits behind the estimate — then check it against your actual bill.
3. Feed-in income — near zero in some states
The days of generous feed-in tariffs are over. Victoria has deregulated its minimum feed-in tariff entirely, meaning retailers can pay as little as $0.00 per kWh for your exports, and rates elsewhere have drifted towards a few cents. A quote that assumes meaningful export income is quietly padding your savings. Our solar rebates guide covers what support is genuinely still on the table.
4. Panel degradation and system losses
Panels lose a little output every year, and real-world conditions (shading, heat, inverter losses, orientation) shave off more. A payback model using year-one laboratory output for 25 years will always look better than one using realistic figures. Ask whether degradation is included and at what rate.
The Solar Sharer wildcard
From 1 July 2026, the Solar Sharer Offer requires larger retailers in NSW, south-east Queensland and SA to offer plans with three free hours of daytime electricity to smart meter households. That changes the payback maths in a genuinely new way: if you can get grid power free from 11am–2pm (12–3pm in SA), the value of solar generation in that exact window shrinks — but power outside the window may cost more on those plans, which solar and batteries can help you avoid.
A good installer should be able to model your payback with and without a Solar Sharer-style plan. If they've never heard of it, keep shopping.
Questions to ask every installer
- What self-consumption percentage have you assumed, and what happens to payback at 10 points lower?
- Which tariff and feed-in rate are baked in — and are they current post-July 2026 figures?
- Is panel degradation included?
- How does the estimate change on a free-midday-power plan?
Confirm the tariff and feed-in figures with your retailer, since plans vary widely.
Why three quotes expose the assumption games
When you only see one quote, you have no baseline. When you compare three, the assumptions reveal themselves: if two installers estimate a six-to-seven-year payback and one promises three, you know exactly where to dig. Comparing quotes side by side is the fastest way to separate honest modelling from sales-floor optimism — something we've seen play out again and again in our solar reviews. For more tricks to watch for, see our solar tips.
Ready to see how the numbers really stack up for your home? Compare up to three free, no-obligation quotes from pre-vetted local installers — get quotes today and put every payback claim to the test.
