The efficiency of the designed micro-hydro pump-turbine unit
over the entire operating range is illustrated in the hill chart shown
in Fig. 4. Overall efficiency contours are given, while guide vane
opening angles are represented by the dotted lines running diagonally
left to right. The best efficiency point was found to be at
EnD ¼ 7.27, QnD ¼ 0.925, giving a maximum overall turbine efficiency
of 79.0%, measured at turbine shaft. This result is in good