Solar payback calculator
Returns a range, not a number, and shows which assumptions produced each end of it. Every input is on screen and adjustable — nothing is chosen for you behind the scenes.
Your installation
Total turnkey cost divided by system size. Use your own quotation.
The all-in energy rate, not the standing or capacity charge.
Set to zero if export is not remunerated or not permitted.
The assumptions that move the answer
Each slider sets the favourable end; the conservative end is derived from it. The gap between them is the range you see in the result.
Check yours against the European Commission’s PVGIS tool for this roof.
The largest single lever. Calculate it from interval data if you can.
A twenty-year price forecast. The conservative case always uses 0%.
Your cost of capital. The favourable case is undiscounted.
What this calculator does and does not do
It models simple payback on self-consumed and exported generation, with module degradation and one inverter replacement in the conservative case. The favourable case is undiscounted with your chosen tariff escalation; the conservative case applies your discount rate, holds the tariff flat, and lowers yield and self-consumption to the pessimistic end.
It excludes storage, grants and subsidy schemes, tax treatment, capacity or demand charges, and any export limitation imposed by connection terms — each of which can change the decision on its own. It is not a feasibility study and not a quotation. Use it to interrogate a proposal, not to replace one.