Alternative Solutions For Powering IoT Devices
A version of this article appeared in the element14 Tech Journal.
In this article, we look at why edge devices need power, and the options for reducing this need to a level where energy harvesting becomes sustainable. We examine some examples of the most popular energy harvesting technologies available, and see how these can be complemented by suitable storage devices.
Powering the edge in a whole new way
Power availability is a big issue for edge devices in many IoT applications – not so much for actuators, but very often for sensors.
Consider, for example, a tracker application in which a device is dropped into a parcel consigned for shipment; the user can track the parcel during its journey and check its progress or even if it has been mistreated. Clearly, no wired connections are possible, so the device must communicate wirelessly while relying on an internal power source.
In other scenarios, edge devices may be located in remote areas, and possibly in large quantities. No mains power is available, while maintenance visits to replace batteries are time consuming and expensive. Edge sensor designers can respond by using rechargeable batteries or supercapacitors together with an energy harvesting strategy to generate charging current for them. Energy harvesting is attractive, as it taps into an inexhaustible supply of ambient energy, but it is also challenging as it may not meet the power needs of the node without careful design.
Therefore, taking every possible step to minimize the node’s power demand is essential in achieving viability for the energy harvesting approach. Even if a standalone battery must be used, power optimization remains important. Saving just a few micro Joules a second can mean changing a battery only after 10 years instead of every year.
Identifying and mitigating edge device power-demand culprits
Edge sensors’ power requirement arises primarily because a sensor device must digitize, package and transmit any measured data to be useful.
This typically calls for at least the sensor, a microprocessor, complete with crystal oscillator, memory array and possibly A/D converter, and the communications interface hardware. A crucial approach to minimizing power demand is to choose a processor that can be efficiently driven into sleep mode when no measurements are necessary, and draws minimal leakage current while asleep. Also essential is the right choice of local network protocol; some protocols may have more data bandwidth than required, while drawing excessive power to support it.
Other techniques for energy reduction are also available; these relate to the choice of processor, memory subsystem, oscillator and A/D converter, as well as coding efficiency.
In many cases, energy harvesting solutions can be used to deliver the power required; either because demand has been successfully reduced using the approaches above, or because ambient energy is available in adequate quantities.
To learn more about some of these solutions, together with some storage technologies that can be used to complement them, read the entire article in element14’s Tech Journal.