September 15, 2009:  Energy harvesting is popularly defined as converting ambient power to electricity to make small devices self-sufficient, often for decades, possibly even hundreds of years. It is certainly not renewable energy on the heroic scale of replacing power stations with grid electricity from the power of the wind, waves, etc. However, there is a middle ground of making things such as trucks and railway stations more energy efficient. For example, regenerative braking and harvesting electricity from shock absorbers and exhaust heat in vehicles makes them more energy efficient. The trans-Australia race involves cars that receive all their motive power from photovoltaics. Japan is already harvesting energy from travellers walking over flexing paving at ticket barriers; this electricity being used to power displays.

Energy harvesting for small devices, renewable energy replacing power stations, and what comes between. (Source: IDTechEx report, "Energy harvesting and storage 2009-2019")

For both the core energy harvesting business and the harvesting within bigger things, the question arises as to what types of energy harvester will attract the big money, creating billion-dollar businesses. Academia is not necessarily driven by commercial potential, so the huge leap in work on piezoelectrics and photovoltaics may or may not be an indication that these types of energy harvesting will come out on top. Other candidates include thermovoltaics (exploiting heat differences) and electrodynamics. There are also dozens of other curiosities such as use of magnetostriction, electrostatic capacitive devices including electroactive polymers, electrets, and so on — doing it all with microelectromechanical systems (MEMS).

Wide variety of applications

All these energy-harvesting efforts are being applied to an impressive variety of applications. Piezoelectrics serve in the gas lighter and the light switch that have no wiring or battery. Photovoltaics appears in calculators, street furniture, satellites, and much more — and now we have transparent photovoltaics in the form of flexible films, converting ultraviolet, infrared, and visible light and other versions tolerant of narrow angles of incidence and low levels of light. All this will hugely widen the number of possible applications.

Electrodynamics has moved from the bicycle dynamo to vibration harvesting, electricity from flexing floors and pavements, micro wind turbines and even powering the implanted heart defibrillator or pacemaker from the heart itself — no need to cut you open to change your battery anymore. Universities should do much more to support this work.

Thermovoltaics is being tested in implants and on car exhaust pipes, not just in engines. Ultralow-cost laptops for the third world employ both photovoltaics and electrodynamics where one project finds that a ripcord is preferred to a crank.

Some energy-harvesting options lean toward the strange. The US military is testing it for robot jellyfish and robot bats for surveillance. So-called wireless sensor nodes are being developed, dropped from helicopters and self-organizing in a self-healing wireless mesh network; applications include monitoring forest fires and other natural disasters as well as pollution outages over vast, inaccessible terrain. Energy harvesting will do away with the need for batteries here.

Counting the dollars

IDTechEx has analyzed a large number of energy-harvesting activities, producing 10-year forecasts for everything from self-sufficient wristwatches to mobile phones that will never need a charger to light switches and controls that have no wiring and no batteries when fitted in buildings. We find that the total market in 2019 will exceed $4 billion (segmented roughly below) — even the niche opportunities are significant.

Estimated value share of technologies in the global energy harvesting market in 2019. (Source: IDTechEx report, "Energy harvesting and storage 2009-2019")

We see a clear route to billion-dollar businesses in photovoltaic and electrodynamic energy harvesting — even ignoring energy storage and associated electronics. The impressive effort on piezoelectric energy harvesting in universities and research centers (such as Germany’s Fraunhofer Institutes) may yet come up with something bigger than that portrayed above. However, as yet, we find it difficult to envisage piezoelectrics powering many consumer items such as wristwatches, mobile phones, laptops, e-books, and others.

The key to wireless sensor networks

While it is generally accepted that 70%-90% of envisaged uses of wireless sensor networks cannot succeed without some form of energy harvesting, replacing short-lived primary batteries in the nodes, it is far from clear that piezoelectrics will be the favored solution here. In military, aerospace, and other industrial and healthcare applications, piezoelectrics has a place, such as harvesting vibration; the piezoelectric light switch and piezo actuators in general have a great future. However, we have difficulty in seeing a large income arising from the harvesting module itself, as is clear with the photovoltaic and electrodynamic applications. Indeed, with these two technologies there are already large commercial successes in 2009.

The greater market

Within the term "energy harvesting" some include extra markets such as ambient power conversion in vehicles and railway stations. In vehicles, it will be thermovoltaics that harnesses exhaust heat. Electrodynamics will harness power from shock absorbers (recently announced by the Massachusetts Institute of Technology) and regenerative braking is already a reality. Moving flooring and pavements generate power from people walking over them, achieved electrodynamically or by piezo power — and the same is true of vibration harvesting in bridges, roads, and aircraft.

Raghu Das is CEO of IDTechEx in Cambridge, UK, and event director of the IDTechEx conference Energy Harvesting and Storage USA, Nov. 3-4 in Denver, CO.