Watch my micro hydro generator system produce 12 amps/ 30 volts at 170 rpms. No pullys direct drive. Low rpm permanent magnet Generator. This generator will last for generations will little maintenance. The bearings and parts are common. Mine is over 12 years old and I have only had to put grease in it once a year. Check out my other video on how to build a simple wind turbine.
Here is a link to the magnets: