Harvesting Wasted Mechanical Energy

Frequent commenter Tim Kingston sent me this very interesting piece (including a very well-made video at the bottom) on harvesting vibrational energy that is currently wasted using piezoelectricity, i.e., the property of some materials that they produce small amounts of electrical power when pressure is applied to them.

I’ve seen many articles on this over the years, but I remain convinced that this is a subject of academic importance only, i.e., that it will never result in anything cost-effective.  Can you insert this stuff in the floors of Grand Central Station and collect a fraction of the energy currently lost as heat as all those high-fliers from Connecticut get off their trains and walk briskly to their midtown offices?  Of course.  Can you do it cost effectively?  Nope.