
Von Stein's invention features a 6.8-kilogram flywheel from an automobile engine mounted to a bicycle frame. The flywheel is driven through a continuously variable transmission in the rear wheel. During charge, the transmission is shifted to increase the ratio of flywheel speed to bike speed. During boost, it's shifted to decrease the ratio of flywheel speed to bike speed. The rider can charge the flywheel when slowing or descending a hill and boost the bike when accelerating or climbing a hill. The flywheel increases maximum acceleration and nets 10 percent pedal energy savings during a ride where speeds are between 20 and 24 kilometers per hour.

Canepa and his team are one of many groups in academia and industry developing technology that can convert wave power into renewable energy to decrease the world's dependence on fossil fuels. For example, the U.S. Energy Department isfunding a project led by Ocean Power Technologies to use the company's buoys to capture wave energy off the coast of Oregon. Likewise, Edinburgh-based Pelamis Wave Power is working with Swedish utility Vattenfall to install Pelamis serpentine-like wave energy converters near Scotland's Shetland Islands to deliver power to 26,000 homes there.
Ref: http://www.scientificamerican.com/blog/post.cfm?id=a-bike-that-uses-its-brakes-for-a-s-2011-06-24&WT.mc_id=SA_facebook