Payback calculator
Two paybacks, side by side
The figure on the left is the one a brochure prints. The figure on the right is the one that survives twenty-five years of degradation, export tariffs, maintenance and one inverter. Change anything you like; both move together.
What is under it
What the model prices, and what it cannot see
Priced in the figure
Generation from system size and annual yield per kWp, degrading at the rate you set from year two onward.
The split between what you use and what you export, at two separate tariffs.
Bill inflation compounding on the import side only, because export rates have not tracked it.
Annual maintenance, every year, for the whole twenty-five.
One inverter replacement in the year you name.
Not priced, and it matters
Half-hourly shape. This is a flat annual model, so a house that shifts load into daylight will beat it and a house that does not will trail it.
Batteries. Storage changes self-consumption, and self-consumption is the single most sensitive input here.
Grant schemes and VAT relief, which move faster than a template can track.
Roof condition. If the covering has ten years left, the array comes down and goes back up inside the payback window.
Your actual tariff on renewal day, which nobody knows.
Next step
Bring us the figure you were quoted
Send the array size, the install price and the tariff on your quote. We will run it through this model and send back the difference, whether or not you ever use us.