When we discussed our home solar panel project in mid-2011 with friends, one of the first questions everyone asked was, “What’s the payback period before you break-even?” The second question was unsurprisingly, “How much is it costing you?” but the focus always ended up on the payback. After all, if you’re going to invest in green technology, you’re hoping that at some point in the near future, you get ahead of the game. It turns out that something we didn’t plan for — our Chevrolet Volt(s gm) — is actually helping us boost the ROI and cut our payback time in half.

Details of the solar panel investment

I shared details on both the solar panel project and the car before, but let me step back and recap a bit. In October 2011, we added 41 solar panels to our southern-facing roof in southeastern Pennsylvania. Each panel is rated…