Energy From Raindrops

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."

who is john galt?

[superwiz (655733)]

well, that's not exactly the galt engine, but it sure smacks of that sentiment.

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[kestasjk (933987)]

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

Lincolnshire could the power house of the world...

[Finallyjoined!!! (1158431)]

The amount of rain we get here. :-)

Portland will be King!

[linzeal (197905)]

Seriously though, 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.

Is this sarcasm or irony?

[mangu (126918)]

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?

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[jdray (645332)]

We in Portland are (as a group) typical of the "think green" group, wherein we want to consume energy, feel good about where it comes from, and not think too deeply about the sensibility of it all. Oddly, solar and wind energy are good (this makes me happy, because I work for a wind energy company), but hydo is bad (think of the fish!). Few people stop to think that they're all forms of solar power. Furthermore, natural gas is okay for heating your home and making hot water, not to mention the popularity

Oblig Gene Kelly reference

[Alain Williams (2972)]

These things don't generate much energy, but should be enough to power a perpetual tiny rendition of Gene Kelly' 1952 hit film.

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[4D6963 (933028)]

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!"

Let's think about this for a second...

[SimonTheSoundMan (1012395)]

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

Re:Let's think about this for a second...

[FroBugg (24957)]

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.

Re:Let's think about this for a second...

[TheRaven64 (641858)]

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.

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[QuickFox (311231)]

It sounds to me like you'd get more energy from this material by having strips of it fluttering in the wind.

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[Adambomb (118938)]

Why not both? Wouldnt a horizontal sheet have only a short list of vectors from which wind would cause no turbulence, so most winds would?

Re:Let's think about this for a second...

[Aaron Isotton (958761)]

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.

Re:Let's think about this for a second...

[ultranova (717540)]

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 [wonderquest.com], 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.

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[ultranova (717540)]

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 :(.

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[maxume (22995)]

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 t

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[It'sYerMam (762418)]

Problem: not all of the GPE will get converted to kinetic. A raindrop is pretty small so it will, I think, have a low terminal velocity. Hence after a relatively speaking short distance, it will lose GPE to friction rather than increasing its speed.

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[It'sYerMam (762418)]

A better idea, perhaps, would be a massive cascade of these things, angle slightly downwards, so that rain would hit, drip off, fall for about a second, hit another, drip off, etc. That distance is about 9/19.6=.45m. So for approximately each additional half meter, you are gaining another unit area.

Our Worries Are Over

[hyades1 (1149581)]

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.

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[couchslug (175151)]

"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.

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[hyades1 (1149581)]

Ah, a Left Coaster, I'm guessing. I have friends and relatives out there. Pale, stoned people who seem to have a lot more fun than me.

This does seem to offer some promise. It would take quite a while, I'm thinking, to slow the planet's rotation by making use of the kinetic energy of raindrops.

And I don't doubt you'd have beaten me to the post if I hadn't noticed just last night how nice it was to have worn waterproof winter boots to the pub.

everything produces energy

[xzvf (924443)]

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.

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[iamhassi (659463)]

"Anything that moves can produce energy. The point is how much and at what cost to capture and reuse or store."

Mod parent up. He's exactly right. I'm tired of hearing about all these hairbrained schemes to find new sources of power, only to read it costs thousands to implement and only creates a couple kilowatt an hour (if that much!), compared to just buying it at the rate of 7 to 10 cents per kWh.

That's why we don't have water wheels [wikipedia.org] on all our drain spouts because you'd never recoup the initial i

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[FooAtWFU (699187)]

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.

Yeah, about that. Does that include your opportunity cost, where you could put that $15k in a very very safe FDIC-insured 4% savings account / CD / money market account, and make $50 a month off it? Then that's more of a... 18-year payback. (Longer if you can get a better return off of riskier investments. Like stocks, and bonds, and such.)

Definitely vapourware ...

[Mostly a lurker (634878)]

... but whether this means it really produces power from water vapour, or is an idea they cannot implement is unclear.

Hey I've got one too!

[skulgnome (1114401)]

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?

Let's do the math on this one

[Ancient_Hacker (751168)]

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.

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[baadger (764884)]

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.

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[Yetihehe (971185)]

It would be better to collect all this 700 000 gallons of water with some roof installed several meters high and run water turbine with water falling down. Of course you have then 700000 gallons of water per day, which you can slightly filter and you hve drinking water. Pure profit, and no ???.

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[Fizzl (209397)]

Furlongs per fortnight?

If at first you don't succeed...

[p4ul13 (560810)]

...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.

The Rain (poem)

[sjbe (173966)]

THE RAIN
--found in Architect's Creek Hut, Westland Nat'l Park, New Zealand

It rained and rained and rained
The average fall was well maintained
And when the tracks were simple bogs,
it started raining cats & dogs

After a drought of half an hour
We had a most refreshing shower,
And then most curious thing of all,
A gently rain began to fall!

Next day but one was fairly dry
Save for one deluge from the sky
Which wetted the party to the skin
And then, at last, the rain set in.

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[flyingfsck (986395)]

Hmm, that sounds like the town I grew up in, which had an annual rainfall of 1000 mm.

Some Back of The Envelope Calculations

[Grond (15515)]

A typical raindrop has a fall velocity of about 8 m/s [madsci.org]. 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.

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[noidentity (188756)]

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.

Pigeon Power!

[GIL_Dude (850471)]

Just imagine: if this stuff panned out, it would not only be rain that could deform it. It could be deformed by say birds walking on it (toughen it against claws). So instead of cities trying to actively chase pigeons away (some places chase them on the ground with dogs and in the air with falcons, etc.) and the "don't feed the pigeons" signs - you would instead see "feed the pigeons right HERE." (where the special plastic is). Hopefully they get some of that rain working for them to, to wash the pigeon poo

Golly, one whole microwatt?

[gregor-e (136142)]

This is more newsworthy as an arcane Rube Goldberg method of extracting energy than as anything remotely practical. You could extract more power by implanting braces of dissimilar metals in the mouths of two teens, then forming a battery when they kiss.

Floors?

[haeger (85819)]

Obviously I didn't read the article, what kind of slashdotter would I be if I did that, but what's with the focus on rain? Why not put something like this where there are lots of people moving about? Shopping malls, trainstations, airports... I'm not sure how much energy it produces but it might be enough to justify the cost. Also it would be locally produced electricity, something that's very high fashion right now.

.haeger

Can I make raincoats out of this?

[mrs clear plastic (229108)]

This stuff would be great for my lighted clear plastic raincoats!

www.clearplastic.com

Just wait till it hails!

[miracle69 (34841)]

Power Surge, baby. Power surge.

Re:I can't believe...

[32771 (906153)]

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 [uic.edu]

"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.

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[The Second Horseman (121958)]

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.

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[mikael (484)]

You have a gutter below the solar panels on the roof. This collects the rain water and funnels it down a sprinkler onto the set of piezo-electric raindrop energy generators. This water then runs off down a couple of water-wheels before being collected into storage barrels, where it is gradually released and drives a micro-miniature water turbine.

Imagine all the energy that is going to be created!!!

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[DavidTC (10147)]

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

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[fbjon (692006)]

You can put it on the south side of the roof (for north hemispherians). Add a wind turbine [windside.com] or a few, and you've covered the majority of weather conditions.

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[TheGavster (774657)]

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.

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[FailedTheTuringTest (937776)]

Terminal velocity for raindrops is around 9 m/s [hypertextbook.com] (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.

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[buanzo (542591)]

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

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[jrmcferren (935335)]

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.