[lygaret]

I was very surprised these weren't piezo or turbine based, but rather harvesting voltage differences in the water droplets itself.

Could a piezo collect current like this, on a solar panel sized sheet? I'd imagine it's not an insignificant amount of power during a downpour.

[ragebol]

What's the velocity and mass of a single rain drop? And how many fall in a square meter in an average year?

Can't do this homework at the moment...