There’s a whole class of devices nowadays that are striving to take advantage of “parasitic power”. Much like the name implies, the goal is to have something live off something else without destroying the host. A self-winding watch is an example that’s been around for decades, as have crystal radios and the spark igniters on some gas grills. A much newer example is the nPower PEG that can charge your mobile phone from the motion of a walker’s backpack.
The PEG works like the shake-type flashlights, using magnets and coils to convert motion into current — something we’ve done since the days of Faraday. The igniter, however, does something much more interesting. It uses the “whacking” collision of a spring-loaded metal bar against piezoelectric crystal to generate a high voltage, which then produces a spark.
The target of this “whacking” in the ignitor is typically a crystal or man-made ceramic, which can be fragile in large sizes. Recently, however, there has been much interest in polymers which are more flexible and generate higher voltages. Additionally, they can be less expensive since they can be created as films or thin sheets. Currently, the front-runner is polyvinylidene fluoride, AKA PVDF.
So, how do you use these devices today in this field of parasitic power?
The answer is any place where you can get access to abundent disposible kinetic energy.
You put them in places where they get periodically compressed, or even better, frequently compressed (as in vibrated). In a road they would generate energy every time a vehicle crossed over. They’re doing this in Israel now.
Or on a sidewalk, every time a person stepped on them there would be a pulse of energy released. The big question is: How much energy do they generate, and why do you want that energy?
In most cases, the desire for use is in a place where it’s inconvenient to use other sources of power and you don’t need much of it. Blinky lights on shoes is a good example. Another use being investigated is sensors placed on shipping containers where they can use the vibration of the truck or ship carrying them.
This isn’t getting power for free, but rather, taking a little energy from something that probably won’t notice it’s missing.