I found this thread via Google search to see if anyone else had thought of the idea, or if there was something already available for rain > electric energy.
For those who think it would be too intermittent to be powerful or practical, that may be true where you live, but I'm a few miles between the rain forest and the ocean in Western WA and 9 months of the year it's pouring down several hours a day. It's not unusual for heavy rain to come down hard for 24 hours straight in the winter. If this relatively small town got serious about rain power we could be selling it back to other parts of the state *without* damming rivers and flooding huge areas and affecting wildlife. We could just *beep* our city drain system!
What I'm thinking of is small turbines that would either be in the gutters as the water comes down, or a whole series of little turbines covering the roof but with larger collection flanges and a drop through a narrow tube above them, to help generate the mass and force needed. Another idea is a large collection tank up at the level of the roof which has multiple spouts - say 10 or 20 that spray the water out when it collects a certain amount, onto the turbines below. I'm sure there are a lot of ways to design such a system, and it's not something I'm really familiar with since I don't work in engineering.
Also I don't think batteries would be essential, as long as the extra electricity could be sold back to the local PUD, it would offset my electric bill, or possibly cover it in whole. It's just ridiculous that the planet is being choked by dirty carbon polluting fuels for our electric needs, when there is so much free solar and hydro and wind and tidal power, more than we could ever possibly need across our planet.
Any help is appreciated.