"We thought of raindrops because they are one of the still- unexploited energy sources in nature," says Jean-Jacques Chaillout of the atomic energy commission in Grenoble, France.
Chaillout and his colleagues realized that every time a drop impacts on a surface it is an opportunity missed. Each raindrop has an impact energy that is highly dependent on the size of the drop; from a small drizzle drop that has 2 microjoules on impact, to a downpour size drop that carries 1 millijoule of impact energy. The team identified that a piezoelectric material might be able to capture that energy. Piezoelectric materials generate an electrical potential when acted on by an outside physical force- say a raindrop. The opposite is conveniently true as well, an electrical charge will change the materials shape, which is how many speakers turn electric signals into vibrations we can hear.
At any rate, in this case the team used a 25-micrometer thick, 10 centimeter long (~4 inch) strip of polyvinylidene fluoride to do the trick. They were able to capture between 1 nanojoule and 25 microjoules of energy per drop (again depending on the size of the drop). The total power will vary incredibly depending on the conditions, but the device produces about one microwatt of power in a light drizzle.
What can you do with this tiny power plant? The authors suggest that this type of device might work quite well for sensors, especially if the sensor is detecting rain, or in a rainy environment. Imagine a weather sensor that would only send a signal of how hard it is raining, when it is in fact raining. Or how about sensors that will automatically close your house windows when a storm suddenly appears?
I imagine this technology will not likely make up a large portion of our energy matrix, but capturing the available energy all around us is certainly a good idea, and presents an elegant solution for remote sensor technologies.