How solar payback works

Payback is a simple idea with several moving parts. First, your panels generate electricity. Some of that electricity is used in your home at the moment it is generated; that electricity is worth the price you would otherwise have paid for grid electricity. The rest is exported to the grid, and you are paid the feed-in tariff for it, which is usually much lower than the price you pay. That is why self-use matters so much: a kilowatt-hour used at home is typically worth several times more than a kilowatt-hour exported.

Second, your annual saving is the value of the self-used electricity plus the value of the exported electricity. Third, payback is your upfront cost divided by that annual saving. If a system costs $6,000 and saves $2,000 a year, the simple payback is about three years. Simple payback does not account for the time value of money, future price changes, or maintenance, so treat it as a first estimate, not a promise.

To improve payback in real life, households often shift flexible loads — washing, dishwashing, pool pumps, electric hot water, and electric vehicle charging — into daylight hours when solar is generating. A battery changes the maths again: it lets you store daytime solar for evening use, which can raise self-use, but it also adds a large upfront cost, so a battery does not automatically shorten payback. Use this calculator with and without a battery cost included in the system cost to see the difference for your own figures.