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ALTERNATIVE ENERGY: Rain Power

Trying to find alternative sources of energy has proven to be an extraordinary feat, allowing us to use everything from sun to the motion of the ocean. But there is still one plentiful source of renewable energy which has so far remained pretty much untapped: rain. Getting energy from falling water droplets might seem like an obvious, ‘why didn’t I think of that’ idea, but so far no-one has really exploited this plentiful (albeit somewhat unreliable) energy source. Now a team from CEA/Leti-Minatec has created a system that is capable of recovering kinetic energy from the impact of falling raindrops.

In a study featured in Smart Materials and Structures, a physics journal, the authors, Romain Guigon, Thomas Jager, Ghislain Despesse and Jean-Jacques Chaillout, write about how it is possible to recover energy from the impact of a raindrop of water. To measure such energy, they built a rain catcher which would allow them to control the amount of water falling on top of a piezoelectric material, in this case made out of polyvinylidene fluoride. A piezoelectric material is a material that is able to convert mechanical energy into electrical energy (see here, and here for other examples where this material was used). Their findings were interesting: slow falling droplets produce more energy than high falling droplets, and as you’d expect, the larger the water droplet, the more energy that was generated.

As for the total amount of power that was recovered? Not much at the moment. Their simulations showed how 1 droplet can generate anywhere between 1 microwatt and 12 milliwatts. What does this mean overall? It is expected that for every square meter of surface, the process could generate about 1 watt-hour per year. This is definitely not going to power your Ipod anytime soon, but there is ample room for progress. After all, piezoelectric materials are still a fairly new technology.

An outlandish idea which at the moment seems unable to produce any significant amount of power? sure! Then again, they did say that about solar power at some point.

+ Rain Power: Harvesting Energy from the Sky @ Physorg

13 Responses to “ALTERNATIVE ENERGY: Rain Power”

Nick Says:

January 30th, 2008 at 5:20 am

I had never thought that rain could have been used to generate energy.
Good article, thanks!

Dave Says:

January 30th, 2008 at 10:08 am

I’d think it would be cheaper and more efficient to put a little turbine at your gutter’s downspout instead…?

Warren Brooke Says:

January 30th, 2008 at 11:37 am

Thanks Dave, I was thinking the same thing in terms of turbines and potential energy.
Just as a preliminary calculation, a rainfall of 1 inch on a 10-storey building with a roof area of 10000 square feet would give a potential energy of just over 10 MJ. I’m sure the rain-water could be stored in in tanks on the upper floors and you could attach whatever size of turbine you want on the ground floor to tap the stored energy. You could have 10 Megawatts, but for only one second, or a 1-watt generator running for 11 days. On more human terms, this energy could power a computer for about 2 hours.

Kevin Says:

January 30th, 2008 at 2:16 pm

One possible application for this occurred to me yesterday, before I had seen this article — use rain power to light up those lines in the road that just happen to be impossible to see when it rains! Will need to work on that efficiency first, though.

Dave Says:

January 30th, 2008 at 6:21 pm

The figure of 1Wh/year was quoted based in the average rainfall in some region of France. In Paris, the rainfall barely gets over 500mm per year. In the tropics, rainfall can reach 10 metres per year and fall for more than 300 days.
This still isn’t very much but for applications like remote seismometers or weather tracking stations it could be more than enough. If solar isn’t an option because not enough sunlight hits the ground, rain power might provide a better solution than running cables out from the nearest village.
Maybe the falling dust on Mars that has covered the solar panels on the rovers could actually produce energy in the same way this rain is.
It’s not entirely clear from either article whether the figure of 12mW for a large raindrop was theoretical based on their computer model or if it had actually been harvested in practice. If there is still plenty of potential left for improvement (like there is in solar technology) then it is definitely worth investing some time into this. If not, it will still have it’s niche uses.

Under the original article, loboy commented that “We already “harvest this energy” later down stream, after the rain has fallen, at a hydro-electric plant.”
This is clearly wrong. The energy of the falling raindrop is all dissipated as heat, sound and (most of it) kinetic energy into the ground. Raindrop in a cloud have potential energy. Raindrops on the top of a mountain have less potential energy but still have some. The energy that a hydro-electric plant harvests is the potential energy caused by the 100m height of the dam, not the 1000m height of the clouds.

jsaving Says:

January 30th, 2008 at 11:44 pm

it seems to me that the higher in altitude you catch the rain the more times you can re-drop it and collect kinetic energy again. really it is collecting energy from gravity. the atmosphere does the work for you.
so if you use gravity to drop that rain repeatedly using chutes or something you would be collecting more kinetic energy.

JT Says:

February 1st, 2008 at 12:01 pm

How does it works ? Could the gravity be used alone ? Would it be possible to put a big rock on the floor and be able to capture the energy that maintain the rock their ? Why would we be waiting for rain ? Could we just install that technology in the tunnels that bring water to the turbines in the dams ?

simon seasons Says:

February 5th, 2008 at 6:32 am

JT , hit the nail on the head, or rather rests his hammer on it.
However, if piezzo electrics is the convertion of mechanical energy into electrical energy then I don’t think we are talking about gravity. Gravity expressed as pressure is not the same as friction which is essentially what mechanical energy is. A familiar Piezzo electric device to those older than say 45 years is the long play vinyle recording that relied on piezzo currents generated in the needle by the movement along the continuous little groove embossed into the piezzo fabric of the ‘record’. The current was tiny compared to the energy needed to move the line around and around, but the friction might possibly be gathered from the tunnels bearing water to turbines, if the tunnels were also made of a piezzo fabric, which they currently aren’t. Thinking further, friction under millions of car tyres might be transferable if the technology goes in that direction, since bitumen is also a piezzo generating fabric or it could easily be enhanced with ingrediants that are more so, like recycled plastic kibble. come to think of it. recycled plastic kibble could be used as concrete aggregate and then you could generate piezzo electrics from lift shafts, supermarket shopping malls, freeways, footpaths,etc.

PaTrond Says:

February 24th, 2008 at 4:17 pm

As Dave said. How much energy can you get out of this anyway?

Gussuero Says:

August 27th, 2008 at 5:27 pm

I am currently moving hair fibers along a rod creating friction, the storing the electric and stepping it up to usable levels. The source i use is the potential differance of pressure at differant hights from sea level. The top of my house is about 30 feet. I use the pressure differance found at thirty from the pressure found at ground level.

dsc Says:

October 25th, 2008 at 6:35 pm

Could this technology also produce electric energy from the vibrations the material would experience if high-frequency sound waves were focused toward it with parabolic sound mirrors? Would appreciate any advice…

gck_salinas Says:

June 4th, 2009 at 5:17 pm

We can avoid either/or thinking and do both :
1. We can first harness the rain drops and convert it to piezoelectric energy
2. Then we collect the rain water and use it run a hydro electric plant.
This was we double the energy we get from the same rain !!