Thank you for the update Agostino. Getting an accurate efficiency graph (“Hill curve”) from a hydro turbine manufacturer is not easy. It may be necessary to determine the efficiency graph experimentally on site after the turbine is installed. This also allows for site variations such as the design of the Draft Tube for the water exit from the turbine. I would like, if possible, to have the inverter automatically adapt to the operating conditions, i.e. vary the torque on the generator and hence on the turbine to find the optimum operating turbine speed. For a fixed pitch Kaplan hydro turbine (propeller turbine) I believe that the point of maximum power production is very close to the point of maximum turbine efficiency – for a given gate opening. Is this true ? Has anyone used an inverter to vary the speed of a Kaplan turbine to determine this ?