I'm working on a project right now which requires a hydro turbine generator system requiring 120W of power output capable of working with the following specs: Flow: 0.003m^s/s Pressure: 6m head By my calculations, this should require an efficiency of ~66%. All flow must be in the axial direction, as the space requirements of the application mean the turbine must be no more than 3" diameter or so. I plan to use a standardized off the shelf generator (if possible) and then design the turbine somewhat from scratch. I will conduct a CFD analysis once I have determined what exactly I should be looking to optimize and what rough blade profile I should be using. I have a few things I am uncertain about though: 1) I would like to use direct drive coupling between the turbine and generator in order to minimize cost and complexity of the system, and I know this will be based on the generator RPM, but what exactly determines the turbine RPM that will be achieved? Also what will determine the torque of the turbine/ shaft/ generator? 2) What more information will I require about the system? At this time I don't know exactly the load resistance that the generator will be connected to. Would this be useful to know? 3) What type of generator should I be looking at specifically? I have seen similar applications (mostly for wind turbines) in this power range that use permanent magnet generators. Would this be the best option? 4) Are there any formulae other than P=Tω and P=ηρghQ that I should know in order to help determine the necessary parameters of the system? Thanks a lot for your help everyone.