A significant factor in the comparison of different turbine types is their relative efficiencies both at their design point and at reduced flows. Typical efficiency curves are shown below.
An important point to note is that the Pelton, Crossflow and Kaplan turbines retain very high efficiencies when running below design flow; in contrast the efficiency of the Francis turbine falls away sharply if run at below half its normal flow, and most fixed-pitch propeller turbines perform poorly except above 80% of full flow.
Part-flow efficiencies
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