Decentralised power networks make communities self-sufficient, and can ensure electricity supply even when national grids are hit by high demand.
The developers of a new ‘wearable microgrid’ hope it could have a similar effect, albeit on a much smaller scale. Developed by nanoengineers at the University of California San Diego, it looks like a piece of space-age clothing – a clean white mock turtleneck, with flexible silver interconnections between small electronic devices on the chest, waist and left arm.
The system is designed to harvest energy from the body, converting it to electricity to power devices. Its developers say it could play a similar role to conventional microgrids, providing sustainable, reliable and independent electricity supply. Forget external battery packs – could our bodies charge our phones and power biomedical sensors?
Sweating the small stuff
The wearable microgrid consists of three main parts – sweat-powered biofuel cells, motion-powered triboelectric generators, and energy-storing supercapacitors. All parts are flexible and washable, and were developed by nanobioelectronics engineer Professor Joseph Wang.
The biofuel cell operates like a battery, with an anode that oxidises lactate in sweat on the chest and a cathode that catalyses an oxygen reduction reaction. Triboelectric generators on the forearms and sides of the torso harvest energy from the movement of the arms while walking, collecting static charges to generate an alternating current, while the supercapacitors store energy from both sources and discharge it to power small electronics.
Harvesting energy from both movement and sweat lets the system work quickly and continuously – the triboelectric generators start work as soon as the user starts moving, and the biofuel cells start providing power when the wearer sweats.
The microgrid was tested during 10 minutes of exercise followed by 20 minutes of rest. The system powered either an LCD wristwatch or a small electrochromic display – a device that changes colour in response to applied voltage – throughout each session. The researchers are also developing designs to harvest energy while the user is sitting down, and other technology could harvest other sources.
“Other potential energy harvesters that have been developed for wearables include wearable solar cells that harvest from sunlight, thermoelectric or pyroelectric generators that harvest from temperature gradient, piezoelectric and electromagnetic generators that harvest from movements,” said Lu Yin, the co-first author of the research paper.
Underfoot dielectric elastomers, which form capacitors as the user presses down on the ground, could offer another option for similar projects.
The wearable microgrid is initially targeted at athletes. Biomedical Internet of Things (IoT) tools could be a promising application, collecting medical information without charging, while consumer applications are a distant possibility.
Powering mini gadgets
“As the concept of 5G networks and the IoT develops, there will be more discrete and miniaturised electronics that have their own independent energy system,” said Yin. “The maintenance of all these small gadgets will become a nightmare without a proper energy solution. As electronics become more miniaturised and their power consumption lowers, it is technologically feasible to design them in a way so they can run independently and be self-sustainable, by harvesting energy from the surrounding environment.”
Wearables expert James Hayward from research organisation IDTechEx said: “The real challenge with all of this stuff is they are harvesting tiny, tiny, tiny amounts of power with these systems – many orders of magnitude less than what is necessary.Frankly it’s such a fundamental problem that these things have got a long way to go.”
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