Sam Redfield of the Appropriate Infrastructure Development Group has designed a bucket-based hydroelectric generator that can be made with easily obtainable, affordable parts. The "pico generator" is intended to provide a modest power supply suitable for home lighting and small appliances to remote destinations. They've already tested the bucket at La Florida in Guatemala, where it demonstrated the ability to power five retro Motorola handsets from hustle'n flow of a small stream.
A modified old car alternator carries out the power generation duties, and the rest of the assembly is made of readily available materials. A small pipe diverts water to a storage tank, from which it is gravity-fed into the bucket. The design also has a minimal environmental and human impact, as it doesn't require damming and feeds the water back into the same stream just a few feet away. [AIDG via Make]