Sunday, September 3, 2006

Follow Up: Harvesting Power from Human Motion at Large Scale

Last year, I speculated about whether it would be possible to harvest power from human motion on a large scale. “On a large scale” was the key part, since devices already exist to harvest power on a small scale, such as combat boots that generate a small amount of power while the wearer walks. To provide a contrasting example, I asked whether one could harvest the vibrational motion of a highway overpass as vehicles passed over.

Lately, architect Claire Price has been in the news with plans to try something along these lines. Here are a few excerpts from a recent BBC article by her:

Reading this, your body at rest is emitting about 100 watts into the environment. If you’re sitting in an open plan office, count the number of surrounding colleagues and you don’t need to be a maths genius to appreciate the possibilities of tapping into all that wasted energy....

“[H]eel-strike” generators, powered through the pumping motion of a footstep, can be embedded within a boot heel. These devices currently achieve upwards of 3 - 6 watts of power output. So the 34,000 commuters who pass through Victoria underground station at rush hour, for example, could theoretically generate enough energy to power 6,500 LED light fittings - energy that today is disappearing into the ground....

Elsewhere in the world, researchers are also looking into how energy harvesting devices can be embedded within roads or how they can be used to create a self-powering heart pacemaker or even an artificial limb....

We [Price’s UK-based firm, The Facility Architects] are applying and testing our ideas practically within a building project within the next year, including a sprung floor fitted with heel-strike generations to harvest the energy from people walking across it. This power output will then be wired back to provide the lighting within that building.

We also plan an LED light fitting with its own micro generator. This unit will convert vibrations from passing trains, lorries or planes to provide continuous light without the need for wiring into the grid.

As of last year, I was unable to find anything on the large-scale version of harvesting power from human motion. So I’m glad that whatever work was/is being done is now in the spotlight.

I hope it succeeds.


  1. Steve,
    I can see the arguments for re-capturing human-generated power, because we're mostly too fat and don't mind the energy expended - or whether energy expenditures go up slightly. But highways are a different matter. Any energy capture device is going to require work, and, by definition, will increase the amount of work done by passing cars, right? If the bridge needs to flex half an inch against some resistant energy mechanism, that half-inch * x force of work is done by the passing car, and is harder for the car to do than the previous de minimus amount of motion of the bridge * minimal (no built-in resistance) or work? Gas mileage goes down ever so slightly, and is this an efficient mechanism for power generation?
    An extreme example -- a car driving up a hill of rollers instead of a road surface -- helps to model out the thought experiment. Maybe I'm missing something here, but TANTAAFL and entropy suggest to me that there's no free lunch here.

  2. Ethan,
    We had this discussion in the comments of the original post. I'm not looking for a free lunch, just trying to scavenge leftovers.
    The concept here is passive harvesting of energy *already present* in the overpass vibrations. That is, today's overpasses are made with materials that already are moving, bending, and flexing (ever so slightly) as a natural consequence of the overpass being used. The question is, can these traditional materials be partially replaced by those that generate power when they move, bend, and flex (ever so slightly)? And, can the power-generating materials be arrayed within the overpass so they massively scale up to exploit the size of structures like overpasses?
    This concept is a nonstarter if the new materials do not harvest existing energy but rather suck extra energy, as with your "hill of rollers" example. But the concept does not require introducing new transducers (like your rollers) or changing the physical interface between the vehicles and the overpass. As things are, the overpass is internally vibrating. Inside the overpass, we want to replace the stuff that's vibrating with stuff that makes power when it vibrates.

  3. On a more humorous note, Adam Carrola, formerly of the Man Show now has a morning radio show that some have tapped as the the heir to Howard Stern...
    One of his recent guests was Ron Popeil, inventor of many late nite TV $19.99 products. Adam suggested his invention: a flywheel in mens urinals, that converts a stream of piss into power.
    Brilliant I say.

  4. I actually had a similar idea:
    I was up at my local shopping centre the other day, and the place was packed. I'm not sure how many cars were in this large 5+ level-carpark, but if there were fewer than 5000 cars in there at the time, with 300
    driving about looking for spots or trying to leave, I'd be surprised.
    On each level in this carpark, and on the ramps between levels there are speed humps -- lots of them -- the aim of which is to keep speeds down to about 15kph (roughly 9 mph US). At the time, the volume of traffic was doing this comfortably enough, but of course, during shoulder periods speeds can increase. In the course of finding a spot
    and then subsequently leaving, I crossed 45.
    It occurred to me that these humps probably do quite a bit of
    cumulative damage to the front ends of vehicles -- the humps themselves are often scarred and gouged from people who for some reason or another were travelling too fast when they reached them but even those who do the right thing are undoubtedly putting more stress on their ball
    joints, axles, shock absorbers etc. Of course, you also end up using energy fairly nefficiently, braking far too much, having the engine turning over at a higher averagae rate than you would if there were no speed hump.
    But what if these humps were replaced with something like a see-saw with a slightly convex underside, about 3.6m/12 feet in length, placed over some medium capable of being compressed -- say a gel, or even water? Then, the momentum or "work" taken from the vehicle could be converted by hydraulic action into the expansion of a series of pistons
    connected to a crank and thereafter a turbine (or flywheel to smooth out the spikes) to generate electricity.
    The owner of the vehicle would lose as much momentum (and perhaps more) going into the see saw device but because the initial impact (all else
    being equal) would be smaller, and because the device would dissipate some of the force of the impact to the medium, the damage to the front end
    would be lowered and vehicles could afford to enter at slightly higher speed reducing the braking required and thus avoiding cumulative recurrent
    costs and even fuel cost.
    If the system could work this way, then everyone would be ahead -- the carpark gets useful energy to sell/use, and vehicle owners get comparatively lower costs. The busier the carpark, the more energy you'd harvest, and since this is peak time, the match is a good one. It even occurred to me that some time well into the future, when EVs were the rule, one could plug in one's vehicle and trickle charge a battery from power generated by these speed pumps, in effect, recovering some of the energy that they've put in.
    I understand it's possible, at least theoretically, to place zinc alloy filaments into a position where applying pressure to them could generate a current as they rub together. Perhaps these could be progressively built into major roads as they resurfaced or were dug up?