In the future we will turn waste energy into work energy. These shocks invented by a bunch of MIT students are evidence of that. A typical truck is about 30% efficient these shocks bump that number up 10%. They work by channeling power from the up and down movements of the piston to create electricity. More specifically the excited hydraulic fluid drives a turbine connected to a generator.
Source
http://www.greencarcongress.com/2009/02/mit-students-de.html#more