et me begin by saying that I am a power electronics engineer and self-described "Energy Efficiency Evangelist." So, although I am an advocate of energy harvesting (EH) technologies, I'm also in favor of anything that helps mitigate energy waste/inefficiencies, hazardous waste (particularly in terms of primary batteries), and non-renewable sources.

One of the truly exciting developments in EH has been the explosion of IoT/IIoT/wearable applications, which are opening more eyes to the capabilities of EH solutions. That's a very good thing.

Historically the rate of adoption of EH technologies has been held back due to two common misperceptions:

The first misconception is that EH provides negligible energy to do anything "real" with it. In general, if you compare EH to battery technology simply from a size and cost perspective, it does have limitations. But the fatal flaw I have observed goes back to that philosophical approach that sets up the choice between increasing the energy source vs. decreasing the system power budgetary requirements. To be fair, batteries are often not given the appropriate consideration in terms of specs and performance for a sufficient analysis to determine power budget margin.  Put more simply, practically any battery-powered design I have ever seen or heard about comes with some "sticker shock" when the first prototypes are received, and realization that the life is not close to the initially calculated value.

The second misperception is that EH exists only as an academic curiosity lacking a production ecosystem. I have observed these common misperceptions since I started getting into the EH world seriously in 2014, and I am pleased to see industry get past these misperceptions to get us to the point we are at today: "Energy Harvesting" is no long a dirty word that draws groans, laughs, and skepticism from the audience, but rather now elicits more curiosity and/or requests for how to implement and expand upon the cost/ benefit analysis.

The fact is that although the EH ecosystem could be considered nascent, that isn't to say that it is only made up of players with a low Manufacturing or Technology Readiness Level. Moreover, the most critical system components have been around for a long time. For example, one of the most key enablers in any EH system is the power management IC, which typically combines the energy extraction direct from the EH source along with power management and even an integrated battery management system or modem (more in the case of SoCs), where appropriate.  Some of the biggest players in the entire semiconductor industry (i.e. – Linear Tech-now also part of ADI, TI, ADI, etc.) have had production solutions shipping for decades.

And, there is the rest of the ever-growing component ecosystem, comprised of all the other things necessary to enable full development. Not only does this include some of the more obvious things such as EH transducers, energy storage, and the things facilitated by Moore's Law (i.e. – ultra-low power, or ULP micros, SoC communications modules, etc.). But also, things that were not obvious early on, such as software and test/measurement techniques.  Advancements in sensors have been key though this can be a real mixed bag of improvements due to things like MEMS and Moore's Law and intelligent power management. In the end, the most exciting thing for me has been the reduction in component power on the load side.

The PSMA Energy Harvesting Committee (EHC) (which I co-chair along with Mike Hayes, Tyndall National Institute) has been working to address these misperceptions in a handful of ways, primarily in the form of education.  From the lowest- to the highest-power systems, it is very common to think an application's needs must be met by implementing a larger power source (i.e. – bigger battery, bigger power supply, higher-efficiency converters, etc.).

But this kind of narrow thinking overlooks the other side of the equation, which comes in the form of reducing the system power budget (either by using lower-power components and/or IPM, to be much smarter with the utilization of what you have—the do more with less approach).

The true disconnect is that most designers do not seem to realize it is typically much lower-hanging fruit to reduce the system budget than it is to increase the available power source.  For example, it can be quite astonishing to see just how much you can do with a single milliwatt of power given today's ULP microcontrollers, sensors, and communications, etc.  This even applies to wireless applications such as wireless sensor networks and IoT/IIoT stuff.

One more example of this kind of oversimplified thinking comes in the form of a question a reporter asked me recently about the range and applications that EH is best suited for today. That of course is the $64,000 question that could be an entire discussion in itself. Generalizing, I would say this can be a very loaded question (thus deserving of a very loaded answer, of course) because far too many of the misperceptions outlined earlier have been driven by the desire to oversimplify EH capabilities/solutions.  Depending on the EH modality, this can also be highly dependent on the operating environment.  One cannot just grab a value from a spec sheet and expect to see the same thing on the bench.  This applies all the way from source (i.e. – huge manufacturing variability of PV cells) to load (i.e. – a BLE modem covering several orders of magnitude from min to max utilization).

The best guidance I can offer is to provide some very rough and relative figures (in terms of typical voltage and power density ranges), which should only be used as a starting point for a general comparison of EH technologies, but not be used to calculate expectations of solution performance. EHC members Lorandt Foelkel of Wurth Electronics and Mike Hayes of Tyndall National Institute have provided some excellent summaries in that regard, which I urge folks to reference.

For engineers looking for additional resources on EH, the PSMA Energy Harvesting Forum  is a great jumping-off point as the committee continues to  populate it with useful resources ranging from design guidance to industry events to key contributors to the ecosystem.  The PSMA EHC is a very open and co-petitive community, so we all win together by bringing EH and related tech to the mainstream!

The Energy Harvesting Committee, as well as all other Technical Committees within PSMA, are freely open and do not require PSMA membership to participate though it is encouraged in order to get access to all of the benefits.  The best way to get involved in the EHC is to reach out directly to myself (bz@powerrox.com) and/or my co-chair, Mike Hayes (michael.hayes@tyndall.ie).  Folks are even welcome to be a wallflower in their first, monthly meeting in order "try before you buy." All that we ask first-time attendees is for an elevator pitch intro.  Other than that, no pressure!

Speaking of PSMA EHC resources, we are currently in the process of putting together a major, comprehensive white paper (led by committee members Thomas Becker of Thobecore and Michalis Kiziroglou of Imperial College London) on the topic that addresses major current issues in detail. The report will be available later this year so keep checking back for that. 

We are also looking forward to the next EnerHarv International Energy Harvesting Workshop. Watch for an announcement in an upcoming issue of the PSMA Update.

I hate to sound like a broken record, but really the education to fight the misperceptions and a maniacal focus on reducing system power budgets (particularly via employing IPM best practices) will really be the biggest difference makers.  There is no magic here and folks just sitting around waiting for a "Moore's Law-like" advancement on the EH/energy storage side of things will be sorely disappointed.

Author: Brian Zahnstecher, PSMA Energy Harvesting Committee Co-Chair

Editor's Note: This article was first published in February 2021 by Fierce Electronics

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