Shaun0007

I installed a 48v unit on my swimming pool pump (1.1kw) outlet as a test and it balanced out the pump usage with a little bit spare.

Just check some of the solar threads for system sizing and getting the right battery sizes.

OK, I would think it would be an idea to try and confine the water somehow, if you put your water wheel in the river and then the water simply flows around it, then that won't work. If you elevate and drop the water, or confine to a sluice you will direct the water onto the turbine better.
Bear in mind that you may gear it up so much that the water can't move it. I played around with a vertical axis wind turbine on an alternator, and getting enough speed was the problem. If you gear it up too much then you basically stall it, too little and it will spin merrily but never get to the point of making usable power. What I also learnt is that chains and sprockets have less power losses than belts and pulleys. I think belts are mainly used in cars because they are quieter.

I quite enjoyed this video a few years back.
There is a few vids like this where guys took a normal Alternator and had a permanent magnet rotor installed. Seems like all of them had pretty good results. Maybe something to keep in mind. 
 
 

Build it first, and the you will know! Odds are you won't get it right the first time, and then tweak and rebuild the turbine. As long as you post some pics 😀