Need help creating a formula. Solar payback years.

[Tomgunn]

I need help with creating a formula that figures Payback Years for solar.

Monthly utility average cost $x that increases by 6% every 12 months.
And the payback years and months it would take to payback $y the upfornt cost of going solar.

I will be using it in a solar proposal tool. I will provide the current monthly utility cost, and the upfront cost of going solar.

The current monthly utiliy cost and upfront solar cost will be unique to every proposal.

[alansidman]

Will the current monthly utility cost be constant? If not, what is the growth rate to use in the model.

Look at this link

http://techtites.com/calculating-pay...riod-in-excel/

Plot the initial cash out put in year zero. (negative value)
In each succeeding year put the cash saving of solar over what ever other utility costs. (positive values)
In another column summarize the cash flows annually until they reach a positive value.