After Tax Cash Flow, Year 15

Why does the after-tax cash flow drop in year 15? is the program assuming the inverter has a 15 year lifetime and needs to be replaced at year 15? If so, what if you have an inverter with a 25 year warranty?

That depends on your inputs. SAM does not make any automatic assumptions about inverter lifetime. If you specify an O&M cost in Year 15 to represent an inverter replacement then you should see that cost in the cash flow.

I think what you are seeing is the effect of the debt period ending -- you might see a change in the annual cash flow after year 15 if the loan period on the Financing page is 15 years.

If you wanted to model an inverter replacement cost at the end of a 25-year warranty period, then you could use the Fixed Annual Cost O&M category with the annual schedule option (click the blue and grey button to open the annual schedule table) to specify a replacement cost in year 26.

Best regards,
Paul.