Every solar quote contains a payback period, and almost none of them show the arithmetic behind it. That is not always dishonesty. It is that the honest answer depends on four numbers specific to you, and a salesperson would rather quote an average than ask you for a bill.
Here they are, in the order they matter.
1. Your all-in electricity rate
Solar does not earn money. It avoids a cost, and the size of that cost is your rate. Take your last bill, divide the total amount you paid by the kilowatt hours you used, and use that number. Delivery charges and fixed fees are part of what you pay, so they belong in the calculation.
The higher your rate, the better solar looks, and it is the single biggest reason identical systems pay back very differently in different places.
2. How much you use, and when
A system sized to your usage beats a system sized to your roof. Overproducing only helps if your utility pays well for the surplus, which brings us to the number that has changed most.
Look at your annual kilowatt hours, and if your utility publishes hourly data, look at the shape of your day. A household that uses most of its power in the evening gets less direct benefit from midday production than one that runs air conditioning through the afternoon.
3. What your utility pays for what you export
This is where old advice goes wrong. Under full net metering, every exported unit offsets an imported one at the same rate, and the arithmetic is simple. Many regions have moved away from that, to arrangements where exports are credited at a lower rate than imports.
Under those terms, self-consumption becomes the point. Using your own production as it happens is worth more than exporting it, which changes the sizing, changes whether a battery makes sense, and lengthens the payback of an oversized system.
Find out which scheme applies to you, and whether it is guaranteed for a period. This one number moves the answer more than the panel brand ever will.
4. What your roof can actually do
Orientation, pitch, shading and available area. A shaded roof does not become unshaded because the quote assumed otherwise, and a single chimney can cost more production than the difference between two panel models.
Ask for a production estimate specific to your roof, with the tool and the assumptions named. Any competent installer produces one. An installer who quotes you a regional average has not looked at your house.
| Ask for | Why it matters |
|---|---|
| Annual production estimate for your roof | The whole payback rests on it |
| Shading analysis | Trees and chimneys are permanent, panels are not |
| Degradation assumption | Output falls slowly over decades |
| Inverter replacement in the model | It will not last as long as the panels |
Ask what happens to the payback if export credit is halved. A good installer has already modelled it. A weak one treats the current scheme as permanent, which it has not been for anyone else.
Batteries are a separate decision
A battery lets you use production later, which under low export credit turns exported units back into avoided cost. That helps the economics but rarely pays for itself on its own at current prices.
Batteries buy two other things: backup power during an outage, and insulation from time-of-use rates. If either matters to you, judge the battery on that rather than on payback.
What a decent proposal contains
- Production estimate for your roof, with assumptions stated
- Your current rate and where it came from
- The export scheme by name, with what happens if it changes
- Every cost including permits, inspection and any roof work
- The inverter replacement priced into the model
- What the warranty covers and who honours it if the installer closes
If a proposal has all six, you can check the payback yourself. If it does not, you are being asked to trust a number rather than to verify one.
Questions people ask
Does solar still make sense without net metering?
Often yes, but the case shifts from exporting to self-consumption. Systems get sized closer to daytime usage and batteries become more relevant.
Do panels need a new roof first?
If your roof is near the end of its life, replace it before installing. Removing and refitting an array later costs far more than doing the roof first.
How much production do panels lose over time?
A small percentage each year, which manufacturers state in the warranty. It is slow and predictable, and any honest payback model includes it.
Are cheaper panels a false economy?
Less than people assume. Installation quality, correct sizing and the inverter matter more to lifetime output than the panel brand does.
