One of the more noticeable aspects of this year's Sensors Expo was the prevalence of energy harvesting. Energy harvesting—using so-called wasted ambient energy and converting it to electricity to power some device of interest—is attracting a lot of attention for long-term wireless sensor network applications.
Why do people care? Well, wireless sensor networking (now that we have radios that work, standards in existence, and larger-scale deployments to play with) is still limited by its power requirements. If you're instrumenting a large facility with a multitude of wireless sensors do you really want to have to go around and swap out batteries on a regular basis? My guess is no. If you could do the same thing without using batteries, wouldn't you be interested?
The other aspect is that, if you can power the sensor nodes using some type of energy scavenging you can now extend the network into more remote areas. Different applications become enabled.
I sat in on the day-long preconference symposia and energy harvesting cropped up in all of them. (OK, so one of them was entirely devoted to energy harvesting, another to wireless sensor networking, and the third to MEMS, but energy harvesting appeared in all three.) What I gleaned from the sessions can be summed up thus: Is energy harvesting technology ready for prime time? No, it's still in the initial development stages. Because the type of technology you choose—whether thermal, vibration, solar, or RF— is heavily dependent on your particular application and its environment, multiple energy harvesting technologies will be required since each particular technology has its own set of trade-offs. According to those who know, there will be few mass markets. Better energy storage technology is vital. And finally, adoption and development will require partnerships spanning the sensor manufacturers, ultralow-power electronics manufacturers, and the makers of the actual energy harvesters.
So Is Anyone Using This Stuff Now?
Yes, actually. EnOcean has been creating and selling building automation sensors that rely on solar cells for a couple of years now, Norske Shell A/S installed GE Energy's Bently Nevada wSIM wireless condition monitoring system that uses battery and self-powered sensors, to name but two. The oil and gas companies are an interesting case because they are awash in vibrating machinery that's operating 24/7, the equipment is generally spread over a large area, the weather is frequently bad, and they have a vested interest in making sure that the machinery stays operational. A self-powered wireless sensor network lets them instrument their equipment more easily and quickly, and provides lots of real-time information on equipment health without requiring their personnel to trek out and check manually or spend time and money swapping out batteries.
There's a lot that needs to improve before energy harvesting becomes just another tool in your arsenal; according to various analysts that point won't come for another several years. However, the technology is out there now and improvements are on their way.