Energy harvesting — technology that can capture and store energy from external sources like the sun and movement — first took hold in wireless sensor networks in industrial settings. Picture a massive factory that uses a wireless sensor network to monitor vital machinery to make sure it remains in top mechanical shape, but instead of using costly batteries that have a limited lifetime to power the sensors, the vibrations emitted from the machinery also power them. While this technology is still gaining a foothold in commercial and industrial settings, it’s starting to look as if energy-harvesting wireless sensors could be entering the home, too.
One promising sign is the fact that the ZigBee Alliance, a trade group made up of stakeholders in the wireless networking industry, is developing a standard for devices that use energy harvesting to capture and store power. It should be published by the end of the year. The standard will define several ways that energy harvesting will work with Zigbee-based wireless sensor networks: It will determine the type of power that the harvester will provide — for example, a light switch that relies on the mechanical energy of a human flicking a switch will create short bursts of power to the network — and it will also help ensure that energy-harvesting devices made by different manufactures will be able to interoperate and will send data upstream over the Zigbee network in a predictable manner.
Ultimately, all of the goals of the Zigbee standard point to bringing down the cost of energy harvesting in wireless sensor networks. And that could help perpetuate the technology into the low-cost needs of the residential home space. Energy harvesting for wireless sensors has been pretty expensive to date, and has been largely only in the price range of a big factory or commercial building. For example, UK firm Perpetuum, which makes devices that capture vibrations and convert them into energy, sells its products to industrial companies for between $750 and $1,000 for various volumes of 500 to 1000 nodes. Widely accepted standards could bring that cost down, and developers could incorporate the technology more into the residential environment.
Zigbee in particular is a wireless standard that has taken dominant control of the residential space. In home-energy management systems, Zigbee is the networking standard for linking smart meters — an estimated 40 million of them — to home area networks. It’s also a leading standard for home health care systems, which rely on sensor networks.
Zigbee is also a technology that is well-matched with energy harvesting, mainly because of its low power requirements. For example, a ZigBee-certified device with an onboard battery can last up to 20 years of use before the battery must be changed or charged, whereas Wi-Fi or Bluetooth devices need to be recharged within a handful of days.
So if battery-powered ZigBee sensors can have such a long life, why bother using energy harvesting instead? Because the energy is there for the taking and in the long run it will save money, labor and reduce hazardous materials, explains Bob Heile, chairman of the ZigBee Alliance. One application of energy-harvesting sensors we’re likely to see in the home building and renovation market: energy-efficient networking lighting systems, which the commercial building market is already embracing. Rather than relying on batteries, Zigbee-powered switches used in home lighting systems can exploit the mechanical energy exerted when we turn them on and off and, therefore, be maintenance free. Plus, Heile notes, more smart devices are entering the home — from remote controls to networked, wireless thermostats and motion detectors that currently run on batteries. These represent more drivers for using energy-harvesting sensor networks in the residential market.
This is not to say that we’ll all be installing energy-harvesting sensors into home area networks starting tomorrow. For one thing, few people have home area networks (something that plenty of energy monitoring system providers are working to change). And for another, many sensors don’t need a battery or an energy harvester, because they plug directly into electrical sockets. However, Cees Links, CEO of GreenPeak, a Netherlands-based chipmaker that makes wireless and battery-free sensors that rely on energy harvesting, sees obvious benefits in using self-powered sensors in smart home applications. Links says energy harvesting would make it easier to distribute sensors in remote or hard-to-reach areas — some of those larger eco-friendly homes — without worrying about maintaining them.
Some companies are even actively looking to tackle this new opportunity of energy harvesting in residential wireless sensor networks. Keep an eye on Schneider-Electric, a French energy management firm that provides energy conservation services for the residential market. Its vice president of Technology Innovation, Frédéric Vaillant, was quoted in a statement from the ZigBee Alliance as saying: “Having energy harvesting devices connected seamlessly to standard ZigBee networks will provide our customers with maintenance-free and even more environment-conscious solutions.” Earlier this year at the ZigBee Alliance’s European Smart Energy Forum in Dublin, Ireland, Schneider-Electric and Philips partnered to demonstrated a light switch prototype that is powered by an integrated energy harvester.
Image courtesy of PMG Perpetuum.