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.

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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