Payback is not a single division. Dividing the investment by the first year's saving gives the right number for year one — but tariffs rise, modules degrade, operating costs accumulate, and under netting rules part of your generation is priced differently. SolarSimPro finds the period by building a year-by-year cash flow.
Comes from the bill of materials and unit prices. Your own design's line items are used instead of a rule-of-thumb per-kWp multiplier.
Yield from the hourly simulation, net of shading loss. The P50 and P90 split shows the optimistic and the cautious end of the payback.
Self-consumed energy and energy exported to the grid are priced differently. Your consumption profile affects payback more than installed capacity does.
Module output falls slightly every year, while maintenance, insurance and monitoring costs accumulate. Both lengthen the period.
The common calculation is investment ÷ first-year saving. That assumes the tariff never changes, the modules never degrade and operating costs are zero. None of the three holds.
In a real cash flow the saving grows with tariff escalation, generation shrinks with degradation, and costs are deducted every year. Once those three curves combine, the payback point shifts away from where simple division put it.
When you consume your own generation you save at the retail price; when you export it you usually receive a lower rate. Two plants of the same capacity pay back over different periods simply because their consumption profiles differ.
That is why the feasibility asks for a consumption profile. A factory running during daylight and a business that consumes in the evening get different results from the same plant.
The period is read from the cash flow that the design and the assumptions build together.
For commercial sites with high self-consumption the typical range is 4-7 years; if most of the generation is exported, the period lengthens. Where you land in that range is set by the consumption profile and tariff, not by installed capacity.
No. Payback tells you the year the investment is recovered and sees nothing beyond it. IRR reduces the return generated across the plant's whole life to a single rate. The two should be read together.
Yes. The annual degradation rate reduces generation slightly each year and flows into the cash flow; you can change the assumed value yourself.
It is. Self-consumed and exported energy are priced separately; once you enter your consumption profile the two are matched against hourly generation.
Finish the design and let the cash flow build itself. Runs in the browser, no installation.