Distributed wireless sensing gets even more attractive if frequent battery changes can be eliminated. That's the whole idea behind energy harvesting (EH). Depending on the system design and the type of energy source used, EH enables the design of wireless sensor nodes to provide data for remote monitoring and control in a variety of areas, without having to consider questions of battery life and replacement.
According to the IDTechEx report, Energy Harvesting and Storage for Electronic Devices 2011-2021 by Dr Peter Harrop and Raghu Das, in 2011, wireless sensors were expected to use 1.6 million energy harvesters, resulting in energy harvester sales of $13.75 million. The report's authors expect the total market for energy harvesting devices to exceed $4 billion in 2021. In addition to the existing strong market within consumer applications, industrial and healthcare EH use are expected to provide substantial growth.
Building automation and automotive are also areas promising significant growth. As part of a building automation system, occupancy sensing can significantly reduce energy consumption. For example, according to Joe Keating, Applications Engineering Manager at Infinite Power Solutions, Inc. lighting, heating, and cooling represent between 54% and 71% of total building energy use. Occupancy sensing can reduce the use of lighting and heating and air conditioning and reduce the annual energy cost for a conference room by half. Wired solutions that cost hundreds of dollars per foot make wireless solutions very attractive—if battery maintenance can be avoided.
EH techniques for converting mechanical or electrical energy, light, or temperature differences into energy for powering sensors include piezoelectric, radio frequency, thermoelectric, inductive coupling, wind, and solar power. However, it takes more than an energy harvester to provide a successful energy harvesting application. Figure 1 shows the blocks of an energy harvesting sensing node that include power management, a microcontroller, a transceiver, and some means of energy storage that can include a battery or supercapacitor.
 Figure 1. In an effective energy harvesting system, all of the power-consuming blocks must use minimal energy to operate within the energy-producing capability of the EH source |
Optimal design considerations and the energy budget are among the critical design aspects in any EH system. For instance, when implementing piezoelectric energy harvesting, the designer must consider random (broadband) vs. predictable (fixed) frequencies. In thermal energy harvesting, the existence of a temperature difference and the magnitude of that change in temperature (ΔT) are essential to effective energy conversion.
Energy Harvesting for Autonomous Systems by Stephen Beeby and Neil Whit was published in 2010. The availability of the book indicates both the increased acceptance of EH and the interest of sufficient readers to warrant a book to explain system requirements. (Note: a few of the chapters are available as a free download when the title is used for a search.)
This year's Sensors Expo will once again have sessions and events that specifically address energy harvesting. The preconference symposium on Tuesday, June 5, 2012, "Energy Harvesting for Powering Sensors - Tutorials," will provide the attendees with a deep dive into the system aspects of energy harvesting. This year's change to a tutorial format from leading suppliers and users of energy harvesting and related system products promises to deliver the details on the latest energy harvesting techniques and what it takes to design a successful EH system.
On Wednesday and Thursday, June 6 and 7, the Energy Harvesting track in the conference sessions will provide attendees with the chance to hear presentations from nine companies that focus on energy harvesting, while the Energy Harvesting Pavilion will allow them to visit the exhibits of companies working in EH. For those looking for more details on the IDTechEx report, co-author Raghu Das will be among the speakers in the sessions. The mix of activities should satisfy those who are curious as well as those who are truly serious about energy harvesting.
ABOUT THE AUTHOR
Randy Frank is president of Randy Frank & Associates, Ltd. and organizer of the Energy Harvesting Symposium and Sessions at Sensors Expo 2012. He can be reached at 480-236-9913 or [email protected].