It's Raining Energy. Hallelujah!

Feb. 7, 2008 -- Energy is everywhere. In the sun, wind, and now rain.

Researchers have developed a technique that harvests energy from rain showers and converts it into electricity. The technology could work in industrial air conditioning systems, where water condenses and drops like rain.

It could also be used in combination with solar power to scavenge as much energy from the environment as possible, or to power tiny, wireless sensors designed to monitor environmental conditions.

"Our calculations show that even in the most unfavorable conditions, the mechanical energy of the raindrops...is high enough to power low-consumption devices," said Romain Guigon, a research and development engineer at the research institute CEA Leti-Minatec in Grenoble, France.

Guigon, who conducted the research with fellow engineers Jean-Jacques Chaillout, Thomas Jager, and Ghislain Despesse, admits rain energy is small compared to that of the sun, but that's not the point.

"It's just a system that can be used where solar energy is difficult to exploit and/or combined with another technology for harvesting energy," said Guigon.

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.

Guigon and his team embedded electrodes into a thin membrane of PVDF, just 25 micrometers thick (it takes 1,000 micrometers to make one millimeter). Then they bombarded the sheet with drops of water varying in diameter from 1 to 5 mm.