For all those looking for some easy peasy NPV calculations I put together a spreadsheet. Please note, I am always open to improvement so if you see something that can make it better please let me know.
Just fill in the yellow boxes (I have locked down discount rate at 10% and inflation at 3%, if you know enough to want to play with that let me know and I will give you the unlock password). Select 10 or 15 year project life, and the spreadsheet will auto manipulate. This is focused around energy savings projects but you can use anything with a cash flow that will accelerate with inflation.