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Energy From Raindrops

Posted by ScuttleMonkey on from the don't-stop-the-rain dept.

conlaw writes to share that according to Discovery.com scientists have found a way to extract energy from rain. A new technique could utilize piezoelectric principles of a special kind of plastic to generate power from falling water in rainstorms or even commercial air conditioners. "The method relies on a plastic called PVDF (for polyvinylidene difluoride), which is used in a range of products from pipes, films, and wire insulators to high-end paints for metal. PVDF has the unusual property of piezoelectricity, which means it can produce a charge when it's mechanically deformed."

30 of 144 comments (clear)

  1. Lincolnshire could the power house of the world... by Finallyjoined!!! · · Score: 4, Funny

    The amount of rain we get here. :-)

    --
    If I had an Ass, I'd call it Fanny Bottom, then I could slap my Ass; Fanny Bottom, on the Arse.
  2. Re:I can't believe... by 32771 · · Score: 4, Interesting

    You are quite wrong, treadmills have been used in the past to power all sorts of things. Here is an example:

    http://www.uic.edu/aa/college/gallery400/notions/histories.htm

    "The hospital of Bicêtre, France boasts a prodigiously deep well underneath, dating from 1735. The horizontal wheel that pumped the water was turned
      initially by twelve horses, then, starting in 1781, by 72 men, taking shifts on a 24 hr day. These workers were eventually replaced by epileptic
      patients and "madmen" in residence at the hospital."

    I would also challenge the notion that fluorinated plastics can be produced energy efficiently enough to actually produce an energy surplus by collecting raindrops. I might be wrong
    though, but out of laziness I'll leave the proof to somebody else.

    --
    Je me souviens.
  3. Let's think about this for a second... by SimonTheSoundMan · · Score: 2

    Whatever happened to water wheels? We have been using them for thousands of years.

    1. Re:Let's think about this for a second... by FroBugg · · Score: 3, Informative

      We upgraded to hydroelectric dams, which provide a very significant amount of power both in the United States and worldwide. China's still working on the Three Gorges Dam, the biggest ever.

      Unfortunately, the US is tapped out on hydroelectric. There really is nowhere for us to put in additional ones, and the ones we already have are often cited as concerns with regards to environmental impact and municipal water supplies.

    2. Re:Let's think about this for a second... by TheRaven64 · · Score: 3, Interesting
      Hydroelectric dams are not quite as good, in theory, as power from raindrops. The sun heats up water, which evaporates and forms clouds. These then fall a long way (lose a lot of potential energy, mostly turning it into kinetic energy and losing some as heat to air resistance) and are caught in a reservoir and lose all of their kinetic energy. They then fall a bit further over a turbine, but by this time they have lost most of their energy.

      Now, if you could build a completely frictionless waterwheel and put it underneath each raindrop, you would get a lot more energy than if you caught the same raindrop in a bucket and then let it drip onto the water wheel (which is effectively what a hydroelectric plant does). There are two problems with this idea. The first is that rain falls over a large area. The total energy from all of the raindrops is a lot, but the individual energy is quite small. The reason hydroelectric seems like a good idea is that, although you only capture a small fraction of the energy from each drop, water falls in to the reservoir from the surrounding hills, so you are capturing rain drops from a very wide area. Once you concentrate rain enough, your losses to friction become a lot less (try building a waterwheel that will spin when a single raindrop hits it, then try building one that will spin when you pour a bucket of water on it and see which is easier).

      This piezoelectric idea is quite neat, because it allows you to capture a significant proportion of the energy from each rain drop and convert it directly into electricity (although you'll probably lose a lot transforming it into anything that you can draw a stable current from). It has the same problem that the hypothetical rain-powered water wheel had, however, and the same problem solar power has: You need a lot of surface area to get a decent amount of energy out. If we assume that it is twice the power output per unit rain of a hydroelectric plant (water falling more than twice the height, but lower efficiency power conversion. Entirely made up number, but probably within an order of magnitude) then it will need half the area of the hydroelectric plant to generate the same amount of power. Note that this isn't just the area of the reservoir, it's the total area that rain falls.

      Some more back-of-an-envelope calculations:

      Annual rainfall where I live is around 1-3 metres (more slightly inland than on the coast). Let's say 2m as an average. Cumulous cloud (the kind that typically causes rain) forms at 2-16km. Picking a number somewhere in the middle, let's say 8km for the average distance rain drops fall. That means, every year, two cubic metres of rain fall 8km per square metre of ground. That's 2,000 litres, which means roughly 2,000 kg. The total energy in this is calculated as mgh, so: 2,000 x 9.8 x 8,000 = 156,800,000 J.

      That sounds like a big number, so let's break it down. Electricity is usually sold in kWh. One W is one J/s, so one kWh is 3,600,000J. That means this gives us 43.5kWh/year energy generation for every square metre of land we allocate for it (note: I am assuming 100% efficiency here, while I would be really surprised if it got 20% in the real world). The average household uses something in the range of 3-4MWh of electricity per year, so you would need 1,000 m^2, or roughly a 30x30m area of land per house. Assuming a more reasonable efficiency, you're looking at somewhere closer to 60x60m, which is still under an acre. Of course, you could probably combine this with solar energy, since solar power is pretty useless when it's raining and so you wouldn't need to supply the entire house's electricity with just this. If they can get efficiency to the 10-20% range, it seems feasible for a lot of uses.

      --
      I am TheRaven on Soylent News
    3. Re:Let's think about this for a second... by Aaron+Isotton · · Score: 3, Informative

      Annual rainfall where I live is around 1-3 metres (more slightly inland than on the coast). Let's say 2m as an average. Cumulous cloud (the kind that typically causes rain) forms at 2-16km. Picking a number somewhere in the middle, let's say 8km for the average distance rain drops fall. That means, every year, two cubic metres of rain fall 8km per square metre of ground. That's 2,000 litres, which means roughly 2,000 kg. The total energy in this is calculated as mgh, so: 2,000 x 9.8 x 8,000 = 156,800,000 J.


      The calculation seems to be correct but the concepts don't hold.

      The *potential* energy of the rain can indeed be calculated using m*g*h as you said. The piezoelectric panels convert the rain's *kinetic* energy to electricity. The kinetic energy on impact is *not* equal to the potential energy, because most of it is lost to air friction.

      As others pointed out, the speed of a rain drop is around 8 m/s. This means that the kinetic energy of your 2t of water is E = mv^2 = 2000 * 64 = 128,000J. You're three orders of magnitude off.
    4. Re:Let's think about this for a second... by ultranova · · Score: 5, Informative

      Annual rainfall where I live is around 1-3 metres (more slightly inland than on the coast). Let's say 2m as an average. Cumulous cloud (the kind that typically causes rain) forms at 2-16km. Picking a number somewhere in the middle, let's say 8km for the average distance rain drops fall. That means, every year, two cubic metres of rain fall 8km per square metre of ground. That's 2,000 litres, which means roughly 2,000 kg. The total energy in this is calculated as mgh, so: 2,000 x 9.8 x 8,000 = 156,800,000 J.

      Unfortunately, this is wrong. A raindrop doesn't keep on accelerating all of these 8 kilometers; it will reach it's terminal velocity, at which point the deceleration due to air resistance exactly cancels the acceleration due to gravity. Since raindrops are small, their surface area is large compared to their mass, so I'd imagine the terminal velocity to be rather small - which is a good thing, otherwise we'd get our skulls crushed to powder by rain, but sadly means that we can't extract all that much power from a single raindrop.

      Actually, I checked, and according to WonderQuest, the average speed of a raindrop is between 2 (for small ones) to 9 (for large ones) meters per second. Since kinetic energy is mv^2, this works out to between 2000kg * 2m/s * 2m/s = 8000J (= 0.002 kWh) and 2000kg * 9m/s * 9m/s = 162 000J (= 0.045 kWh) per square meter per year.

      Since the price of electricity is about 0.07 euros per kWh where I live, and a square meter of this thing would need about 22 years to produce a single kWh under optimal conditions and assuming a 100% efficient conversion, I don't think that it is a good investment.

      --

      Forget magic. Any technology distinguishable from divine power is insufficiently advanced.

    5. Re:Let's think about this for a second... by ultranova · · Score: 2, Informative

      Hups ! That should be 0.5*mv^2. So the above figures are twice as good as they should be - it's going to take 44 years to produce a single kWh per square meter :(.

      --

      Forget magic. Any technology distinguishable from divine power is insufficiently advanced.

    6. Re:Let's think about this for a second... by maxume · · Score: 2, Interesting

      The distance that the raindrop falls is irrelevant when calculating the energy available when it hits the ground -- the velocity is what matters. You are imagining that you can capture the entirety of the potential energy that the raindrop contains before it starts falling, when in reality, you are limited to capturing the kinetic energy it contains when it lands. So if air resistance happens to slow the drop down, you are losing energy well before the drop ever gets to your system. Googling says that the terminal velocity for a drop of rain is generally less than 10 meters/second.

      From velocity=acceleration*time, you can infer that the rain drop is reaching that velocity in about a second, after falling about 10 meters(OK, so it would be going slightly slower than 10 m/s and have fallen somewhat less than 10 meters, whatever). So your availability calculation should be 2000*9.8*10=196,000 J, a factor of 800 less than what you stated. So if your device is 100% efficient, my still generous estimate is that you would need 800,000 square meters, not 1000, which is more like 900 meters on a side, and more like 200 acres.

      --
      Nerd rage is the funniest rage.
  4. Our Worries Are Over by hyades1 · · Score: 5, Funny

    If they put this stuff on the floor around the urinals at my local bar, we could meet Canada's energy needs for the next hundred years.

    --
    I've calculated my velocity with such exquisite precision that I have no idea where I am.
    1. Re:Our Worries Are Over by couchslug · · Score: 2, Funny

      "If they put this stuff on the floor around the urinals at my local bar, we could meet Canada's energy needs for the next hundred years."

      If they trapped the runoff from under the urinals at your local bar, they could sell it as American beer.

      --
      "This post is an artistic work of fiction and falsehood. Only a fool would take anything posted here as fact."
  5. everything produces energy by xzvf · · Score: 2, Insightful

    Anything that moves can produce energy. The point is how much and at what cost to capture and reuse or store. I can solar panels on my roof for about 15K that averages about $120 a month. About a 10 year payback. A wind turbine that generates about 20% of my needs would cost 5K and have a payback of 15 years. Strapping a motion generator to myself and family to produce enough power to charge cell phones doesn't appear to ever justify the initial cost. Raindrop system.... call me when it costs the same as a shingle.

  6. Re:meh by The+Second+Horseman · · Score: 2, Insightful
    Because with this, you can just put them on the roof! Under the solar panels! Oh . . . wait, no. On top of the solar panels! No, that won't work either . . .

    Seriously, though, if it actually worked, it might be an alternative in a spot that gets enough rain / regular cloud cover to reduce the attractiveness of solar. I guess.

  7. Re:Ideas! by buanzo · · Score: 2, Funny

    Heh. How long until ThinkGeek start selling the ShowerBuzzer with Self-Power option? :P

    --
    Buanzo Consulting - 15 Years of GNU/Linux experience, for you.
  8. Hey I've got one too! by skulgnome · · Score: 2, Funny

    Let's build a very large vat. I mean it has to be huge. Then collect lots of rainwater in it, and stick a mechanism that changes outflow into something that can be used to spin a generator. Boom, electrical energy from rain!

    Of course this is still just indirect-indirect-indirect solar power, as always. But jeez, do you have to make things so complex by default? Is this the "innovation-promoting" effect of patenting?

  9. Re:Oblig Gene Kelly reference by 4D6963 · · Score: 2, Funny

    should be enough to power a perpetual tiny rendition of Gene Kelly' 1952 hit film.

    Would that be "Watching 'Singing in the rain' in the rain"? That would make a catchy song! "I'm watching Singing in the rain in the rain, I'm watching Singing in the rain in the rain, what a glorious feeling, I'm happy again!"

    --
    You just got troll'd!
  10. Let's do the math on this one by Ancient_Hacker · · Score: 4, Informative
    Hmm, raindrops... Why didn't someone think of this before? For a good reason:

    • Let's be generous and assume it's raining all the time.
    • And it's a real gully-washer, say an inch an hour.
    • And let's be really generous and assume this gadget captures 50% of the energy of falling water.
    • And each raindrop is at maximum terminal velocity, about 10MPH.
    • So that's about 700000 gallons of water per day per acre falling at 10MPH.
    • Which works out about 6 million pounds per acre per day at 10MPH.
    • Which is about 100 million foot-pounds per day per acre.
    • But that's only 1157 foot-pounds per second, barely 2 horsepower.
    • Roughly 750 watts at 50% efficiency.
    • Or roughly 17 milliwatts per square foot.
    • Or at ten cents a kwh, it's making almost 100 watt-hours a year, or almost a penny.
    1. Re:Let's do the math on this one by baadger · · Score: 2, Interesting

      Another way of looking at it is a 1 inch puddle of of water covering 1 acre is going to weigh approximately 100 tonnes. Falling at 10 MPH, (~4.5 m/s) and using E = 0.5mv^2 the maximum amount of kinetic energy here is approximately 1 Megajoule, which over an hour is about 280 watts.

  11. If at first you don't succeed... by p4ul13 · · Score: 5, Funny

    ...this breakthrough comes after failed attempts to generate power from roses, whiskers on kittens, bright copper kettles and warm woolen mittens.

    These are a few of those researchers favorite things.

    --
    Paul Lenhart writes words!
  12. Some Back of The Envelope Calculations by Grond · · Score: 4, Informative

    A typical raindrop has a fall velocity of about 8 m/s. Assuming a pretty healthy rainfall of 10cm (4 inches) we get 100 liters of water per square meter of land. 100 liters of water weighs 100kg, of course, and plugging that into the equation for kinetic energy gives us 6400 joules. Spread out over 2 hours, that's a whopping .89 watts per square meter.

    All of that assumes 100% conversion efficiency and no losses due to standing water absorbing the impact of the drops. If the overall efficiency is, say, 50%, then you'd need something like 30 square meters to light a single compact fluorescent bulb. To generate a megawatt would require over 2 million square meters (over 500 acres).

    Given that in most places it rains less often than the sun shines, this seems like an astonishingly inefficient way to generate electricity. There just isn't that much energy in rainfall.

    1. Re:Some Back of The Envelope Calculations by noidentity · · Score: 2, Insightful

      Given that in most places it rains less often than the sun shines, this seems like an astonishingly inefficient way to generate electricity.

      But it's a great way to generate research money.

  13. Re:why rain? by jrmcferren · · Score: 2, Interesting

    Why not put into floors of buildings, that way the building get energy from people walking around. Also put in in sidewalks that way the same principal would work for people walking on the street.

    --
    sudo mod me up
  14. Is this sarcasm or irony? by mangu · · Score: 2, Insightful

    Portland is trying to gain the title of the renewable energy capital of the United States and this would be awesome in the whole Pacific Northwest as they slowly ween themselves off the major dam systems they build up over the past 80 years

    Do you mean hydroelectric power isn't renewable? Hydro power *is* energy from raindrops, where do you think the water in the rivers came from?
  15. Re:meh by DavidTC · · Score: 2, Insightful

    That's almost enough energy to hoist it up there in the first place!

    --
    If corporations are people, aren't stockholders guilty of slavery?
  16. Re:who is john galt? by kestasjk · · Score: 2, Insightful

    (It's worth noting hydroelectric dams have been used for power generation for a long time now)

    --
    // MD_Update(&m,buf,j);
  17. Re:meh by TheGavster · · Score: 2, Interesting

    Collecting the water and running it through a mill only takes advantage of the drop from the roof to thr ground, where this device takes advantage of the larger drop from cloud level. That said, there's no reason that you can't line your collection pan with this stuff and still use waterwheels in downspouts. I'm also guessing that a waterwheel can do a better job of extracting energy than this plastic, so for taller buildings (closer to the cloud/farther from the ground) I can see turbines winning out.

    --
    "Because Science" is one step from "Because old book". Try "Because of my experiment testing my falsifiable assertion".
  18. Re:meh by MadnessASAP · · Score: 2, Informative

    I'd be willing to bet that a raindrop reaches terminal velocity in a very short distance making the difference in height between a roof top and a cloud irreleveant.

    --
    I may agree with what you say, but I will defend to the death your right to face the consequences of saying it.
  19. Re:Lincolnshire could the power house of the world by ZeroFactorial · · Score: 2, Funny

    Electricity and water.

    What could possibly go wrong?

  20. Just wait till it hails! by miracle69 · · Score: 2, Funny

    Power Surge, baby. Power surge.

    --
    Linux - Because Mommy taught me to Share.
  21. Re:meh by FailedTheTuringTest · · Score: 3, Informative

    Terminal velocity for raindrops is around 9 m/s (slower for smaller drops, like drizzle). Acceleration is 9.8 m/s/s. So big raindrops reach terminal velocity in 9/9.8 = 0.9 seconds, during which time they fall 0.5*a*t*t = 0.5*9.8*0.9*0.9 = 4 metres = 13 feet.