Energy harvesting: challenges for wireless monitoring applications
Energy harvesters deserve the attention they're receiving, the advent of what can be made possible through the use of ambient energy to power devices has intrigued a wide variety of technologists, developers and adopters.
Potential hurdles, challenges, and requirements influence the rate of adoption of energy harvesting and sustainable energy technologies. IDTechEx technology analyst Dr. Harry Zervos recently met with Dr. Roger Hazelden, technology specialist on sensors and optoelectronics, at TRW Conekt.
Although TRW is mainly involved with components and systems for the automotive industry, the company's involvement in energy harvesting goes beyond vehicle applications. TRW research includes roadside infrastructure sensors for monitoring traffic, potential accident hazards, accidents and its effects on roads, etc. TRW's Swiss branch also is researching and developing its own thermoelectric generator.
As a supplier of tire pressure monitoring systems (TPMS), TRW uses 60-cent batteries instead of energy harvesters, which could cost several tens of Euros. According to Hazelden, cost is a major driver in applications such as TPMS's where batteries use is unregulated; a low cost coin cell will always be preferred over an expensive energy harvester. Energy harvesters would make a lot more sense in applications where there are restrictions on the use of batteries (such as aerospace), in which case they would be part of enabling technologies that would make wireless sensing/monitoring a reality.
At an energy harvesting workshop on May 4, Kenichi Soga, Professor of Civil Engineering from the University of Cambridge gave insight on the use of monitoring for structures that were built in the past with a "let's build them and see how long they last..." approach. Several of these structures are a few decades old and pose potential risks if their integrity is compromised over time. An interesting example of use of integrity sensors in a project was during some work undertaken for the London Underground, ensuring that tunnel tiles did not shift or move, leading to width changes that could be detrimental to passing trains or even fears of collapse. Again, interestingly, batteries were used for these sensors, provided by Tadiran technology. At a cost of about £40 for the battery and £200 for the whole sensor, batteries were considered, the best, most reliable option, with a lifetime of approximately 2 years, and the sensor taking measurements at a rate of 1 measurement/minute.
High costs for energy harvesters, reliability of new technologies when compared with established ones, advances in existing competing technologies (such as batteries and supercapacitors) as well as convincing potential customers of the advantages offered by new technologies as well as identifying the correct harvesting solution for the correct application tend to be recurrent challenges for the energy harvesting sensor.
It is not always easy to compete on the merits and added benefits of new devices, especially when an additional cost accompanies them. Initial costs of ownership and infrastructure necessary can add to the skepticism towards adopting innovative solutions. What tends to be important in efforts to alleviate skepticism is the use of proven solutions as examples that can convince of the real value behind the initial installation expenses. EnOcean's implementations are a great example of this and that can be seen from the large numbers of customers that have adopted the company's solutions (over 160,000 buildings are currently using EnOcean products, from wireless light switches to occupancy sensors and sensor networks for both building and industrial facilities). Such successful implementations raise the profile of energy harvesting technologies and increase awareness of potential users and the interest in finding elegant solutions to problems that cannot be solved without energy harvesting.
IDTechEx Energy Harvesting & Storage and Wireless Sensor Networks & RTLS Europe 2011 conference was held in Munich on June 21-22.