The stand-alone principle advocates that project analysis should focus on incremental variable total sunk You decided to get into the alternative energy movement and purchased for $750, through a catalog, a solar panel for the roof of your house. An electrician charged $250 to install the panel on your roof and connect to your home electrical system. Your spouse gets the Mastercard bill and starts badgering you for spending $1,000 for some useless invention. "Just wait", you say. After 1 year from installation, your Ameren/UE bill has decreased by $300. You get up on a ladder and trim a tree that has been shading the panel from late afternoon sun. At the end of the second year, the Ameren/UE bill shows a $480 energy savings. Your neighbor, an engineering professor at UMSL, suggest you move the panel two to three feet higher on the roof. This really helps the panel and your electric bill is reduced by $520 in the third year. Your spouse is now bragging to the neighbors that your home will probably be "off the grid" soon because of the solar panel on the roof. A friend is interested and asks what the payback period was on your $1,000 investment. You reply: O 3 years, 2 months, and 27 minutes or did you want the discounted payback? 2.15 years, and mind your own business! The only payback was seeing my spouse look forward to the arrival of the electric bill in the mail Hell, we're still paying that Mastercard bill; you know Mastercard charges 19.5% on the unpaid balance. 2.42 years, give or take a couple of days