
From Technology Review published by MIT...
"Shock absorbers that generate electricity, which are being developed by  Cambridge, MA-based Levant Power, can lower fuel consumption by 1.5 to 6  percent, depending on the vehicle and driving conditions. The system  can also improve vehicle handling.
Levant has demonstrated the technology in road tests with a Humvee and  will expand testing to trucks, buses, and other vehicles this summer.  The shock absorbers look like conventional ones from the outside, except  for a power cord coming out of one end, and they can be installed in  ordinary vehicles by mechanics. They plug into a power management device  that can also manage power from other sources, such as regenerative  braking systems, thermoelectric devices that convert waste heat into  electricity, or solar panels. The power is then fed into the car's electrical system to  reduce the amount of load on the alternator."
Read more here