Solar Payback Calculator

What this calculator does (and does not)

This calculator gives you a quick sense-check on solar economics. It uses sensible defaults: 870 kWh/kWp annual generation, 40% domestic self-consumption (75% commercial), 7p/kWh SEG export rate, no electricity-price inflation, no tax adjustments. Your real payback depends on four numbers that change the answer significantly: your specific self-consumption ratio, your specific import tariff, your assumed electricity inflation, and your tax position.

For a real proposal, we run our cash model with your specific MPAN data, your half-hourly consumption (if HH-metered) and your tax position. Most KMM customers find the real payback is slightly better than this calculator suggests — primarily because we model electricity inflation at 4% per year (which has actually averaged 9.2% over 2010-2025).

How to interpret the result

• 4-7 year payback (commercial): strong. Solar will be net-positive on cashflow within 5 years.
• 8-12 year payback (domestic with battery): typical. Most family homes land here.
• 12-16 year payback (domestic without battery): borderline — the system still pays back inside its 25-year warranted life, but the payback is sensitive to import tariff changes.
• 16+ year payback: probably not worth doing as a pure financial play. We'd recommend either upgrading your usage pattern (heat pump, EV) to lift self-consumption, or waiting for either a price change or a regulatory change.

Solar payback calculator FAQs