All of us rely on batteries in our daily lives to power everything from our cell phones to our tablets to our notebook computers. We may take them for granted, but because we refer to them frequently we're aware (in most cases) of when they need recharging or a top-up from a portable power bank.
But when it comes to industrial devices, things aren’t always quite so easy. Indeed, the proliferating sensors that underlie the Industrial Internet of Things (IIoT), present a key energy management challenge for several reasons, including:
- Access because of the physical location of the device. (One thing a wireless transmitter can do is be installed where it would be challenging to put a wired device.)
- Notification because all devices notify that their power supply is nearing end of life, but is it soon enough to schedule a replacement?
- Process impact and the need to coordinate operations/maintenance to potentially isolate the device by putting associated operations into manual while work is being done, (Though for a monitor-only point this can be part of the work permitting process.)
Presently, battery technology has a shelf and useful life of approximately 10 years. As we know, however, environmental factors—particularly temperature—affect battery life once in service. Both hot and cold temperatures adversely affect battery life, with Canadian (0 ºC/32 ºF) or Gulf Coast (30 ºC/86 ºF) installations suffering 10% and 15% reductions, respectively. On the other hand, cryogenic (-40 ºC/-40 ºF) processes and their steamy (85 ºC /185 ºF) counterparts are likely to suffer 30% and 50% reductions, respectively.
Meanwhile, the impact of signal update rate on battery life is negative (as expected) but non-linear. Relative to the once-per-minute update standard, battery life decreases 20% to update every 32 seconds, 50% to update every 16 seconds, and about 60% to update every 8 seconds. This means that, although increasing your update rate decreases battery life, manufacturers have designed the systems to help maximize availability.
Energy demand on a device at the center of a wireless mesh network is quite different than that of an edge device. Mesh network design recommends a minimum of two neighbors/three descendants (two neighbors plus gateway) for path reliability. Therefore, assuming a simple case of one node (center) needing to update at twice the rate of its neighbor further away from the node means the center node battery life will be 20% less than the edge node because it's sending the extra messages. If the center is updating from two other nodes, then its battery life will be 40% less.
Demand on the rise
All these factors need to be considered when thinking about battery life for any installation. I just used wireless networks as an example because it's one of the faster growing industrial demand areas, and therefore one for which information is available.
Of course, once your batteries have served their useful life, they must be disposed of properly because they contain rare metals. In the European Union, Directive 2006/66/EU on “Batteries and Accumulators and Waste Batteries and Accumulators” controls batteries containing mercury, cadmium or lead, and has been in place for many years, so they can be recovered and recycled. Because manufacturers sell globally, their mandated markings are likely on your batteries as well, so they can be properly recycled.
Increased use of lithium-based batteries has created a demand for lithium as well as a market to recycle these used batteries, so their metals can be recovered for reuse, especially the larger batteries used in EV and hybrid vehicles. This trend will impact industrial installations, too.
Of course, with all this demand for improved energy storage, research into alternate configurations and materials to increase energy density and battery life are coming closer to reality, and will be transferable to smaller form factor applications, such as those used for industrial control.
About the author: Ian Verhappen
