by Mike Fahrion
Wireless data networking solutions can be far more cost effective than their wired counterparts. Power and data cables are expensive to install – often more expensive than the connected equipment itself. It’s hard to get cables across rivers, roads, railroads and parking lots. Things will stop working if a cable breaks, but installing redundant cable connections can be prohibitively expensive. I recently looked at an application where it cost $150 to install and provision a $400 wireless network gateway. That’s certainly more expensive than “Zero Touch Provisioning”, but it was much cheaper than running cable. Providing that gateway with external power would have cost an additional $1,200, just to wire a single device.
Fortunately, wireless technology has now evolved to the point where it can finally be entrusted with mission critical data. For example, I’ve been working with a wireless sensor mesh network technology that can achieve a 99.999 percent reliability rate in real world conditions while operating on an average power budget of just 50 microwatts – even when publishing data once per minute. Not bad.
At that level, I can easily substitute a battery for a power line. Most people would be quite content with that. But I’m still left with the nagging feeling of engineering imperfection. Even at 50 microwatts a battery won’t last more than 10 years, tops. If I want a “forever” wireless solution, what are my options?
I could start with energy harvesting technologies. Consider solar power, for example. A high efficiency PV cell that’s just a few inches across can give me enough power for many indoor wireless applications. There’s even more light energy available outdoors. But I’d still have two problems.
The first problem is darkness, of course. No light, no power. If I’m indoors, I’ll probably need enough energy storage to get me through a long weekend of “lights out” in a commercial facility. If I’m outdoors, I’ll need enough storage to get through a long night. That will call for a battery or a supercapacitor. But if you read the fine print on the life expectancy of your energy storage components, especially if they’re used in a wide temp range application, you’ll find that we still don’t have a “forever” solution. The storage component might be able to last as long as 20 years, but that would be hard to validate.
The second problem with solar harvesting is the installation procedure. I’m not going to be the author of a quick start guide that reads, “Set your sensor in a sunny spot for 60 minutes before continuing to Step 2.” Nor do I want to say, “Install the wireless node, drive home, and hope that the node will come online when it charges up.” So what’s the solution? We need another battery to get the product through its setup/provisioning/validation process while it waits for its energy harvesting source to come on line.
What if I try a different power harvesting technology, like thermoelectric? I’ll be facing similar problems. The node will need to be “live” when it’s installed, and if I lose my thermo energy source for any reason, I’ll lose my data connection. Once again, I’m going to need a backup power source: another battery.
Either way, my quest to create a “forever” wireless product would include the additional cost of an energy harvester and two energy storage elements, both of which will eventually wear out, just as if the device was operating on battery power alone.
The perfect wireless solutions of the future will include Zero Touch Provisioning, so that installers don’t need to be RF experts or skilled technicians of any kind. They will eliminate all power and connectivity cabling, even for devices like network gateways. And they will be truly energy independent, able to operate indefinitely by harvesting power from the immediate environment. Zero Touch Provisioning and cable replacement technologies already exist. But don’t sell your battery stocks just yet. Wireless solutions may already be eliminating cables and the need for specialists who understand provisioning wireless devices out in the field, but they’re still a long way from completely eliminating the humble battery.
For now, just be sure that “batteries are included.”
Originally written for Remote Magazine – http://www.remotemagazine.com/main/articles/batteries-included/
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