That may be a long project, like carving an airplane propeller from scratch, with no prior knowledge. Getting the optimum match between the alternator and the pelton wheel (I assume) AND the water flow and head pressure, will take a LOT of trial and error. That's why I bought my Harris Hydro alternator and pelton wheel combo some years ago, and it worked right out of the box. It has an adjustable field strength (I believe that is what it is called) because if you get too ambitious and load the rotor down too much by making too amps, you lose rpms, there is a sweet spot where everything clicks, and a lot of not so sweet spots where they don't. That, and switching out the jets is how you fine tune things. More power (ha ha) to your friend in his project, don't want to be a wet blanket....but there is a lot more going on there then initially meets the eye is my point.