The Zigbee Alliance has produced a green power option - no AC or battery power required - in the latest ZigBee specification. By I.D. Scales.
The other great thing about ever-lower silicon power consumption (apart from the obvious planet-saving lowering of power consumption in data centres and on the desktop) is that you can theoretically get closer to an 'initiate and forget' IoT world because it gets ever more feasible to have modules do without batteries or AC power. Instead you can onboard clever technologies to 'harvest' energy from other, inexhaustible sources.
The advantages of this development for M2M/IoT are pretty obvious. ZigBee, which has included this battery-ousting, power harvesting option in its latest specification, points out that there are often cost limits to the number of sensors that might be deployed and managed for an application, ruling out some large-scale projects. Doing without wires or batteries just makes mass deployment and subsequent maintenance cheaper and easier.
In some environments (explosive and flammable, for instance) ultra-low-power harvesting might also be preferable to AC or batteries for obvious reasons.
The ZigBee specification enhances the IEEE 802.15.4 standard for M2M/IOT applications by adding network and security layers and an application framework. This latest enhancement, 'Green Power', is now an optional addition to the ZigBee PRO feature set. The spec allows battery-less devices to securely join ZigBee PRO networks using motion, light, vibration and other more esoteric sources yet to be developed to provide power for an attached module.
ZigBee says energy harvesters can be divided into two categories: bursting and trickling. "Bursting energy harvesters can generate too much energy very quickly. Trickling energy harvesters create just enough energy continuously over a long period of time. Bursting energy harvester examples include piezo-electric elements, dynamo/electro-mechanic converters or vibrators. Trickling energy harvesters include solar cells and peltier elements that leverage temperature differences."
One bursting option, for instance, is to harvest left-over energy from the flicking of a light-switch. It's claimed that, with the right technology, a switch flick could generate enough power to send commands through a ZigBee network.
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