http://www.inhabitat.com/2008/01/30/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.