Could we be getting loads of extra power from kinetic energy?

July 10, 2013 8:28 PM

I just got an automatic watch and the fact that it powers itself via small movements of my wrist has me fascinated, and also puzzled that we haven't really taken more advantage of obtaining small amounts of power via changes in kinetic energy (if thats the right term?)

The only examples I can think of is automatic watches, some hybrid cars which get energy from braking, and the lights people use on bicycles which get energy from the wheels turning.

Is it because the machinery to capture the energy isn't worth the small return we'd get? Or some other reason I totally haven't thought of?

posted by Admira to Technology (22 answers total)

Best answer: Tidal electricity generation is a more ambitious example. But I recall being told that it turns out to be really practical only in a few places.
I'm sure it also has some environmental impact.
posted by thelonius at 8:37 PM on July 10, 2013

Hydroelectric power (waterfalls) and wind power both work on this principle, don't they?

I think the issue is going to be what generates the kinetic energy in the first place. We need a big source of movement that's happening already (like tides), so that we don't have to expend power to make the movement.
posted by LobsterMitten at 8:40 PM on July 10, 2013

Best answer: The kinetic energy has to be unwanted, else you just need to expend more energy than necessary to move the thing you want to be moving, and getting some of that extra energy back. Cheaper to not put in the extra energy in the first place. So the places where it's advantageous aren't as common as you'd think. But the military was/is playing with backpacks that slide up and down as you walk, which could increase gait efficiency while taking energy out of the system - a rare win-win, normally these ends are in opposition and zero sum.
posted by anonymisc at 8:43 PM on July 10, 2013 [1 favorite]

A watch battery provides a remarkably small voltage/amperage and can last up to multiple years. The utility to payoff with a watch is pretty high, in that it's already a prestige item and the amount of energy needed is so small that activity in a day may power it. Unless you're me, and leave a watch off your wrist too many days. If you search on the web, watch winding machines exist. Because people own multiple watches, and they still die after a number of days due to inactivity.

The other issue is storage versus immediate use. Bicycle lights powered by movement use the energy near-instantly and don't require the immense energy exchange of (much) battery storage.
posted by mikeh at 8:43 PM on July 10, 2013

Best answer: I don't know if it's exactly what you're thinking of, but along the lines of getting power from things that are already happening anyway, there's a patent on a system of highway dividers that function as wind generators, driven by the drafts of passing cars. I don't know if the patent is by the same team, but I saw it a few years ago in Metropolis magazine. I don't know if it's been implemented yet.
posted by LionIndex at 8:46 PM on July 10, 2013

Best answer: There's lots of MEMS piezoelectric vibration energy harvesters being designed to drive small, power-sipping remote sensors, e.g.
http://www.hindawi.com/journals/smr/2012/853481/. Check google scholar and the physics arxiv for more info.
posted by sebastienbailard at 8:51 PM on July 10, 2013

Response by poster: So I'm going to start with saying I know this idea is probably rubbish or we'd have already done it. But I thought of shoes. Lots of people have shoes with cushioning, impact absorbing etc. If the energy of that impact was captured with each step and stored ... we could plug our phones into our shoes to charge them? I'm guessing the requirements to store the energy, when combined with the very small amounts, mean its not practical.

Essentially I'm thinking of what LionIndex said "getting power from things that are already happening anyway", I love the examples of using the tide, the highway dividers etc.
posted by Admira at 9:00 PM on July 10, 2013

Best answer: The Army/Darpa has looked at shoes.

There's also the flutter mill

I'm guessing the requirements to store the energy, when combined with the very small amounts, mean its not practical.

It's important to ask "just how many watts do we get out of this widgit? At what point has it finally paid off the debt of the embedded energy it took to fabricate and started producing a net surplus?"

Those greenwashing baby turbines on rooftops are an example.
posted by sebastienbailard at 9:11 PM on July 10, 2013

The problem is that you can get small amounts of power a lot of places, and there are a number of things that use relatively small amounts of power, but it's usually so much easier to just plug them into a wall outlet or dash board and use a microscopic fraction of the power available there.

The place where advances of this type are going to be handy is in places where tapping into much more powerful systems isn't going to be possible or convenient. Hence we see this kind of stuff happening with DARPA, and things being marketed to hikers and in the third world.
posted by Kid Charlemagne at 10:18 PM on July 10, 2013

Best answer: Not technically harvesting kinetic energy directly, but a teenaged girl invented a flashlight that gets charged by body heat. (It's a lot easier when you only have to power LEDs, of course.)

If the energy of that impact was captured with each step and stored ... we could plug our phones into our shoes to charge them?

Yup. Some people are way ahead of you.

I think, as with the flashlight, and the advent of wearable tech and other small devices, we are going to see more of this sort of thing -- in a lot of cases it may even be invisible. But the other part of the problem is that the means to harvest kinetic energy are not necessarily themselves even as cheap as the devices they are designed to power. So convenience becomes an issue again, and it's only economically viable for situations where regular, ubiquitous commercial power is not available.
posted by dhartung at 11:24 PM on July 10, 2013 [2 favorites]

Best answer: From memory there are speed bumps or sleeping policemen that generate electricity for road signs. I wouldnt be without a hand cranked radio and torch.
posted by BenPens at 12:54 AM on July 11, 2013

You are asking a typical engineering question, which has the ever-present economic component.

To the engineering question... there's a lot of wasted energy 'out there', coming out of all sorts of physical processes. To capture it requires non-recurring engineering to design the capture and storage mechanism. It then requires the recurring part which has its own set of economics related to how many are produced and how the costs fall out.

Centralized production and distribution of power make general purpose power possible. Remote production, storage and use depend on an economically viable mix of non-recurring engineering, recurring costs of production of the local infrastructure, and the comparable costs of the more conventional alternative.

The short answer is "Yes, you can power stuff with parasitic or environmental power". No big deal.

The longer answer adds "..., but it has to make economic sense or provide some feature than cannot otherwise be obtained."

All design is tradeoffs. Power is no different.
posted by FauxScot at 5:26 AM on July 11, 2013 [1 favorite]

Best answer: Saw that this was just posted today, timely! - Human Motion Will Power the Internet of Things, Say Energy Harvesting Engineers
posted by estlin at 6:53 AM on July 11, 2013

Best answer: But I thought of shoes. Lots of people have shoes with cushioning, impact absorbing etc. If the energy of that impact was captured with each step and stored ... we could plug our phones into our shoes to charge them?

The shoe thing is being worked on as well.
posted by JoeZydeco at 7:11 AM on July 11, 2013

Best answer: Machines that harvest floor vibrations can be used in building construction. Here's an article from 2006 talking about that, but note that it's been 7 years since that article and stuff like that is still "innovative". It's a great idea, but it's difficult to implement, especially in a way that the money you spend on installing these harvesting devices isn't a huge overinvestment compared to the cost of the electricity you'd otherwise use. A building can pretty easily be hooked up to the power grid, but changing/recharging batteries is annoying, so powering all the lights in a building by vibrations doesn't have as much immediate payback as smaller stand-alone objects where the harvested ambient power is replacing a battery, like a lightswitch that uses the force of your button-push to power a wireless signal to the thing you're switching, or using the vibrations of the floor as a self-powered occupancy sensor.
posted by aimedwander at 7:24 AM on July 11, 2013

Best answer: This device claims to charge a battery using kinetic energy similar to your watch that you can later use to charge cell phone etc. No idea how well it works.
posted by samhyland at 8:22 AM on July 11, 2013

Best answer: they had a great demo of pedestrian powered sidewalk lights set up at the Olympics

http://www.cnn.com/2011/10/13/tech/innovation/pavegen-kinetic-pavements
posted by bobdow at 8:23 AM on July 11, 2013

Best answer: There are also gymnasiums purporting to generate electricity.
posted by seemoreglass at 9:31 AM on July 11, 2013

Best answer: Also, one place that tidal power is practicable is off the coast of Maine.
posted by seemoreglass at 10:30 AM on July 11, 2013

Best answer: Lots of people have shoes with cushioning, impact absorbing etc. If the energy of that impact was captured with each step and stored ... we could plug our phones into our shoes to charge them?

That's the goal of the SolePower Kickstarter.
posted by radwolf76 at 2:47 PM on July 11, 2013

they had a great demo of pedestrian powered sidewalk lights set up at the Olympics

Neat as an art project-consciousness raising piece, unless one's intent is to make people think about energy production and environment, I would guess the ROI on watts/dollar and so on is better when one puts one's money and matter into solar panels, wind turbines, etc.
posted by sebastienbailard at 4:43 PM on July 12, 2013

Thad Starner in '96 investigated several forms of power generation from the human body, including body heat, blood pressure, breathing, arm motion, walking. http://www.cc.gatech.edu/~thad/p/journal/human-powered-wearable-computing.pdf
posted by at at 10:05 PM on July 13, 2013