Batteries not included: How small-scale energy harvesting will power the future

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Running man: Human motion energy harvesting

So far we’ve seen a trio of concepts that are apparently ready to help reduce our dependence on traditional power sources but generally do not have the oomph to fully replace those sources. That trend continues for our fourth and final entry, biomechanical “human motion” energy harvesting. That’s right, this technology harnesses power from the mere act of moving. Wanna charge up your Android? Better start swigging that beer a little faster.

Jesting aside, it turns out that biomechanical energy harvesting isn’t quite the novel idea it may initially seem. Remember those old-time bicycle headlights that would pull power from a generator tapping into the rotation of your tires? That was a perfectly decent – if not absurdly tiring – example of the same process.

But way down in the southern hemisphere, they have a slightly different take on the subject. Here, at the Biometrics Lab in the Auckland Bioengineering Institute, dedicated folk huddle in the darkness (and in the brightness too – this is no witch’s coven) to devise a better way. They think they’ve found it.

“The trick, and this is where our group comes in, lies in controlling these generators to produce useful energy using circuits that are small enough and light enough for portable applications.”

Their idea, at least initially, does away with the bicycle element altogether and asks that you get walking (or running) instead. Ben O’Brien of SoftGen, the company that’s currently springing to life around the concept, provides more insight.

“For portable electronic devices, we want to capture otherwise wasted energy so that the user doesn’t feel the extra load. For example, when we walk around, the soles of our shoes compress. This compression requires energy, energy that is lost as heat. If instead we replace part of the sole with a soft generator we can capture this energy and convert it to electricity.”

Like all the technologies we’ve showcased, the fundamental SoftGen idea has been with us for some time already. In the case of “heel strike generators,” as they’re called, that time frame stretches back decades. But SoftGen has added a new wrinkle in the form of “artificial muscle generators.” Invented in California at the turn of the millennium, artificial muscle generators are, O’Brien and company believe, the spark that takes heel strike generators into the future.

softgen demo artificial muscle generator electricity power
An artificial muscle generator. The user pushes the rod, which directly deforms the muscle inside the box and produces electricity.

“The basic idea,” explains O’Brien, “is to apply electrical charge to a deformed elastomer membrane. When the deformation is relaxed, the charge is boosted to a higher energy state. By cycling the deformation and controlling when you put the charge on and off, you can generate power with approximately 10 times the energy density of competing technologies. All this with something as simple as a piece of rubber.” “The trick, and this is where our group comes in, lies in controlling these generators to produce useful energy using circuits that are small enough and light enough for portable applications.”

O’Brien plays down the concept of a completely battery-free future, saying that energy needs to be “smoothed out” and stored for periods of lesser activity. As for “simple” early targets for SoftGen’s brand of energy harvesting, O’Brien says heel strike generators “could power bright lights for safety at night, electronics embedded in the shoe (a la the Nike+ product range), and medical monitoring for podiatrists,” adding that, “Our particular niche is low-powered applications. We’re working to have the technology in a real-world consumer product soon.”

There seems to be no shortage of accessible energy on tap when foot strikes ground. In The Energetics of Running and Running Shoes, Martyn R. Shorten claims there may be as much as 10 joules (1 joule = the work required to produce one watt of power for one second) of wasted energy per each running step. This, of course, is music to the ears of folks like O’Brien. “Theoretically, if you could capture all of this, you could fully charge a smart phone off a single shoe in a half hour run. And your shoes wouldn’t feel any different than they do now.”

O’Brien welcomes alternative energy harvesting technologies, recognizing that what might be a great fit in certain situations or with certain people won’t be panacea for everyone. “The great thing about human motion power is that it’s always available where we are. This might not be a big deal when you go home at the end of the day and have easy access to a wall socket, but as the number of electronic devices we carry grows, it becomes a nuisance to charge them all. Now consider all the times you’re not next to a wall socket, or if you’re travelling in a country with different plugs, or you’ve gone off the grid – tramping or hiking – or due to poor infrastructure or after a disaster. In all these cases, human motion power becomes a very attractive concept.” 

[Image credit: Auckland Bioengineering Institute]

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