A particular group of miniature power generators consists "of devices that recycle energy available in the ambient. They are referred to as scavengers. Typical ambient energy sources are heat or mechanical vibrations." In an IOT environment this becomes even more urgent. Already we can talk of The Monster footprint of digital technology: "When we talk about energy consumption, all attention goes to the electricity use of a device or a machine while in operation.
A 30 watt laptop is considered more energy efficient than a 300 watt refrigerator. This may sound logical, but this kind of comparisons does not make much sense if you don't also consider the energy that was required to manufacture the devices you compare.
This is especially true for high-tech products, which are produced by means of extremely material- and energy-intensive manufacturing processes. How much energy do our high-tech gadgets really consume?"