Capturing lost energy with regenerative braking systems is one thing. This, however, is another ball-game entirely. Researchers in Israel have been experimenting with power generators placed underneath the road's surface to capture the mechanical energy of cars passing above and turn it into electricity.
I just ran across this very in-depth article that introduces us to a new team, the Technion Israel Institute of Technology, Haifa, who hopes to rewrite the record books when it comes to solar aviation. They are doing so with a rather small airplane (compared to previous solar fliers) known as SunSailor.