SAM system payback info

I am trying to learn how to use the SAM for residential PV systems and payback and today I have looked through a lot of the training pdfs but cant seem to quite get it. I still plan on looking at some more info to try figuring out everything but am hoping I can find someone off line to show me how to use the calculator. Is there someone in the Denver area that may be interested in explaining this.or someone that would explain it quickly on the phone...maybe someone at NREL? I have made a spreadsheet that I use now to show payback because I have not been able to find anything that seemed to be accurate, including PVWatts. Please let me know if someone has an easy explanation that isnt like 1000 pages of reading with terms that I dont understand. I was not a finance major in college, I am an installer so please KISS...maybe there is a class I can catch locally?
Thanks,
Jeff

There are a couple of reasons that SAM's payback calculation is not as simple as the following equation:

Payback Period (years) = Project Investment ($) / Annual Cash Flows ($/year)

1. Annual cash flows are not constant. For example, a project with a 30-year life may have tax-deductible debt interest payments in the first 15 years, periodic O&M costs every 7 years (e.g., for inverter replacements), and incentive payments in the first 10 years).

2. SAM calculates metrics besides the payback period (levelized cost of energy, NPV, etc.) that are based on a cash flow that includes debt costs, so it uses a different cash flow to calculate those metrics. In the base case cash flow table on the Results page, SAM shows the "after-tax cash flow" that it uses for the LCOE and NPV calculations, and the "payback cash flow" that it uses to calculate the payback period.

To address Items 1 and 2, SAM defines the payback period as the time in years that it takes the cumulative payback cash flow to equal the project investment cost.

If you look at the payback and cumulative payback cash flows at the bottom of the base case cash flow table on the Results page, you can see that the payback period is in the year when the cumulative payback switches from negative to positive. The Year Zero value shows the initial investment amount (a negative number). The Year One value shows the sum of the Year One cash flow and the initial investment, Year Two is the sum of the Year One cumulative cash flow and the Year Two cash flow, etc. As the years progress, the project's cash flow pays off more and more of the initial investment. When the cumulative payback turns positive, the initial investment is paid off.

Best regards,
Paul.