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Piezo Electric energy harvesting project

Discussion in 'Alternative Energy' started by lazcook, Nov 24, 2008.

  1. lazcook

    lazcook New Member

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    Its been a long time since I’ve posted on here, but I have a question for anyone familiar with piezo generation!

    I am using piezo ceramic strips to generate energy from vibrations, with the aim of charging a battery over many hours that will eventually power an LED when there is enough power. A very small current is generated (0.1-0.2ma ) so to provide a constant flow I have built a step up circuit with 4 capacitors to build the output to a current of 1ma at 0.3-0.4 volts. My issue at the moment is trying to stored this constant flow of power over time to eventually power a single LED so any suggestions on how to store the current would be appreciated!

    Question:
    1. What type of supercapacitor would be suitable for this application? I have been speaking digikey and they have sent me these data sheets about super capacitors but I don’t really know what would work: I have uploaded them, please see the links: http://www.canterburyyoga.co.uk/electronicsresearch/P1543.pdf and http://www.canterburyyoga.co.uk/electronicsresearch/P1544.pdf

    2. Can anyone suggest a particular LED that needs low current and voltage to operate?

    Thanks in advance for your replies- I am a industrial design student doing a research project in Loughborough University!
     
  2. Hero999

    Hero999 Banned

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    How long do you want to power the LED for?

    If the current in is only 0.2mA then you can't get 1mA continiously unless you reduce the voltage. Remember P = IV and there's no such thing as perpetual motion, useful energy out is always less than useful energy in.
     
  3. lazcook

    lazcook New Member

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    hi hero,


    the project is a pavement slab that generates energy to power a light during darkness- so for around 7 hours. It will be in an busy urban area so will have constant power everytime someone walks over the piezo paving slab unit. I can use multiple units together and it looks like I will need a large number to generate the correct power, it could be 6 paving slabs each with 10 piezo units? thanks for your reply.
     
  4. dave

    Dave New Member

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  5. Endolith

    Endolith Member

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    I was thinking of making something pretty similar to this, too. You really need a switching power supply to use up all the energy in the supercap, though, since its voltage decreases quickly as it discharges.

    A simple example would be the "Joule thief" that uses up all the energy in a battery down to 0.35 V to drive an LED (which requires at least 2 V).

    Make a Joule thief.

    Are piezo strips an efficient want to harvest energy from this motion, or are there better ways to capture it?
     
  6. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    Another people powered energy system! :)

    The actual impact of a human foot step is rather slow and spread out so the transfer of recoverable energy from it is incredibly small! A full day of people walking over a city block of piezo electric transducers would probably not even light up one compact high output LED for more than a hour or two.
    Spending tens of thousands of dollars and many hours of human effort to convert one city block worth of sidewalk over to get a hour or two of light in a 100 sq ft area would not be very practical and never cost effective. One roof top solar array with the whole city blocks lighting system set up with LED's would be way cheaper and far more practical and cost effective.

    The typical energy the sun puts down on a square foot of earth is around 15 -60 watts per hour over the seasons.
    Even capturing 5% of that energy over a 12 hour period is several magnetudes of order or higher than that of the capturable energy that human foot steps can create inthat same area.

    I did this writeup a while back but to give you the more realistic numbers to how people equate to usable power I though it would be a worthy repost.

    Why Humans are poor sources of energy.
    Here is a real life or more toward real life power example. one horsepower = 746 watts. Horsepower in its simpler definition is thats the continuous power a good sized healthy horse can produce. Scale that to good healthy human and you get 1/10 that or about 75 watts continuous. Remember thats continuous rate not peak rate! For a short burst a big healthy athlete can top 1500 watts on one of those generator bikes. I have seen a college football player do it! but for only a few seconds. I could do around 1200 watts at the time but again short burst. One person did 200 watts for about five minutes, A cyclist and great cardio health too.

    A person walking without effort is real low, under 10 watts. The only time most people even get close to the 75 watt output is taking the stairs. And how many do that by choice!
    Convert Calories to watts. 1 calorie is 1.16 watt hours. So a 2000 calorie a day diet means the average person runs on 2320 watt hours of power. Factor in the estimated calorie drain of just being alive is around half of that or more. You have less than 1 kw of mechanical energy to put to work per day.
    So how many people does it take to equal what your average house uses? mine is around 1200 kwh a month. 1200/30/24 = 1.6666 kw continuous load. hmm, I would need about 23 very healthy slaves to keep my house going. give them 8 hour shifts and I would need 69 plus support to feed and keep up everything, now I am up around 80 plus!
    Convert that to lazy free will people and its probably ten times that! hmm... hmm... hmm!!! 800 people to run my house! But now who is running their houses while they run mine?

    But seriously people power is just not cost effective. There is a reason slaves got replaced by machines as the world industrialized.

    Sorry if I just rained all over someones idea. again.
     
  7. Sceadwian

    Sceadwian Banned

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  8. Endolith

    Endolith Member

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    I don't think you're even talking about the same thing, actually.

    And yes, human power in general is feasible. Check out Bionic Power, for instance, which generates 2.5 W without any exertion by the human.
     
  9. Sceadwian

    Sceadwian Banned

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    You can't generate power without causing drag, I think you mean minimal, not no exertion. I personally think the best place for these kind of bionic generators is in shoes, where the resistance will act as a shock absorber in the first place, free energy by sucking up what would be bad for the legs/spine.
     
  10. Endolith

    Endolith Member

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    The human body uses energy to move, but it also uses energy to stop. Biology hasn't evolved an equivalent to regenerative braking, so this can be used to generate energy while reducing the energy used by the human:

    "Just as a hybrid vehicle recovers power from the energy of braking, the Bionic Energy Harvester takes advantage of the "negative" or energy-absorbing work naturally performed by leg muscles during walking. Rather than creating resistance that demands additional effort, the device actually helps muscles do their locomotive work by engaging only during the "braking" phase of the leg's swing when muscles are acting to decelerate the limb."

    That's what most people think of at first, yes.

    "Previous and existing devices that harvest energy from human movement focus on either the compression of the heel or the shifting of a mass carried on the back. The former approach generates little power, while the latter approach only works while a heavy weight is carried. Early in the design process, Bionic Power's bionic engineers concluded that the most productive energy-harvesting site for walking is the knee joint. The knee has more displacement than the heel"

    Anyway, this is very different from the original poster's idea.
     
  11. Sceadwian

    Sceadwian Banned

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    I bet it feels weird wearing one of those things. I think compression of the heel could produce more power if taken advantage of properly. The thing about the knee bit is it ONLY generates power from walking. A heel generator would generate power as people shift their weight around while standing all day. Only a very small portion of the population walks enough to take advantage of the kind of power that device generates.
     
  12. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    Its apparently feasible but like the guy said in the follow up comment s cost Vs real life price justification of implementation will never get close to a break even point.

    It can be done but other than as a novelty its never going to be practical to build, maintain and get a justifiable return out of it.
    I just have to go with the general concept that profit by someone is what ultimately justifies a product for sale and implementation. If you want to build and install them at a financial loss I will happily build and install them for you!

    As far as the human dynamic braking concept.
    Too many of us are too fat and lazy as it is! The fattest and laziest ones need that self braking effort for exercise! ;) :)

    My repost was meant more to be an example of how much average energy a typical persons daily life style takes and how that equates to people power in general.
    On the real scale of power consumption by the human race and when compared to other types of alternative energy, we humans are just too inefficient and underpowered (even worse using passive energy capturing and conversion systems) to be anywhere close to being a practical power source.
    On pound for pound scale comparison, bugs put out more energy for their weight and size than we do! :eek:
     
  13. Mr RB

    Mr RB Well-Known Member

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    You can generate electricity from just about anything. But for something to be worth doing it's got to be cost effective dollar/watt/lifespan.

    Piezos are very expensive vs the amount of power they produce, they are delicate and unreliable as the shock forces that produce the power are similar to the shock force that breaks them. And putting power generation electronics right under walkways where it's subject to water ingress and big shock forces just seems dumb.

    Power generation is generally done best at large scale, with the best dollar/watt efficiency, then distributed. How much does the electricity cost to run a 1.5v led at 1mA for 10 hours a night?

    What about chemical based luminescent markers? They could absorb free solar energy during the day and glow all night. Easy to install and replace on a per unit basis, no wires or systems needed.
     
    Last edited: Apr 30, 2009
  14. sirwilliamjr

    sirwilliamjr New Member

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    I know it has been a while since the original post, but I am working on a similar project, except I am working with flow induced vibration from wind converted to electricity using piezos for my MS in ME at Georgia Tech.

    I have (relatively) just begun, and haven't done much with super caps, but I can recommend this design: Harvest Energy Using A Piezoelectric Buzzer. I haven't built it yet, but it's a starting point.

    Regarding LEDs, I have had some luck with high brightness LEDs such as R20WHT-V-3045.

    I can't remember what my power levels are, but they are sub mW on the average, so peak (no storage cap) is maybe 1 mW.

    Hope this helps some.

    How is the project coming?

    Will
     
  15. Endolith

    Endolith Member

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    Have you seen the windbelt?

    Windbelt - Wikipedia, the free encyclopedia

    Maybe something related to piezo fans could be done:

    [​IMG]

    [​IMG]
     
  16. sirwilliamjr

    sirwilliamjr New Member

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    My project is pretty much a piezo-fan in reverse (although not exact because that sort of flow is not reversible).

    Thanks for the lead with the Humdinger Windbelt. I had seen that when the inventor first showed his product, but I had not seen his more recent versions.

    Similar to the fan, my devices are free at one end. One problem I have run into is breakage from excess wind load. Although it is designed as it is for a different reason, the windbelt would seem to help this problem.
     
  17. Endolith

    Endolith Member

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    Yeah, I was imagining a windbelt with piezo fans at each end instead of magnetic generators.
     
  18. Sceadwian

    Sceadwian Banned

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    Endolith how much energy do you get out of that little gumstick one, and how much air needs to be going across it to get it?
     
  19. AMITESH PANDEY

    AMITESH PANDEY New Member

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    hello lazcook jst joined this form because saw your idea and hey i am also working on this concept but with PVDF material could you post some of oyur circuit diagrams as i need it badly
    thanks in advance......
     
  20. Endolith

    Endolith Member

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    It's a fan, not a generator. I don't think it would do much in a breeze, unless you combined it with a resonant thing like the windbelt.
     
  21. small_mirror

    small_mirror New Member

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    hey, im working for this concept too. i just started. can you give me some guidance? is there any way i can contact u easily?
     
    Last edited: Dec 10, 2010

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