Have heard this being proposed from time to time over the years, but it never happened. The power involved was always too low and the electricity too cheap. Good to know it is still possible for particular on-demand applications. Some intriguing details here.
Why Sweat Will Power Your Next Wearable
Biofuel cells can generate enough watts for fitness trackers and health monitors By Patrick Mercier and Joseph Wang in IEEE Spectrum
Admit it—you love your smart watch and all the amazing things you can do with it. But the task of keeping it charged can be annoying. A longer battery life would be great—but with batteries, the amount of energy stored correlates with volume, and bigger batteries add bulk and weight. All wearables, including fitness trackers, audio-enhancing hearables that go in your ear, and augmented-reality contact lenses, have a similar power problem. And today’s batteries are too bulky and stiff for use in wearables that are woven into textiles or directly mounted on a user’s skin.
The power demands for these kinds of devices range from 1 milliwatt for a basic step counter to tens of milliwatts for more advanced smart watches. When using small, centimeter-size batteries, which have capacities on the order of 10 to 300 milliampere hours, this results in battery lifetimes of only a few days at most.
Some researchers are tackling the wearable power challenge by developing new types of stretchable batteries and supercapacitors. However, it’s hard to produce such batteries using screen printing, a process that dramatically lowers costs. Other developers are trying to bypass batteries altogether by using Near Field Communication chipsets for wireless power transmission. But NFC technology requires you to have an external power source, like a mobile phone, within a few centimeters of the wearable; once you move the phone away, the wearable stops working. ... "
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