A wind farm comprised of 10 wind turbines E-40 (see power curve below) operates in a remote network. The average wind speed for a given day can be assumed to be 5 m/s from 00:00 to 08:00, 12 m/s from 08:00 to 16:00 and 10 m/s from 16:00 to 24:00. Experience has shown that the best efficiency of the E-40 wind turbine is about 75 % of that of an ideal turbine. The rotor design to be used is a three-bladed rotor, which results in a downstream velocity equal to a third of the upstream wind if the tip speed ratio is = 6.0. Air density can be considered as 1.225 kg/m. Power (kW) 600 550 500 450 400 350 300 250 200 150 100 50 0 ENERCON E 40 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Wind Speed (m/s) Figure Q1: Performance curve of the ENERCON E40 wind turbine (a) Calculate the efficiency of the turbine at = 6.0. Is this the best efficiency of the turbine? (b) Determine the rotor diameter required for the proposed wind turbine. (c) Determine the rotation rate of the rotor. (d) Estimate the wind energy production during this day and the corresponding energy surplus if the daily energy demand is 3 MWh from 00:00 to 8:00, 32 MWh from 8:00 to 16:00 and 14 MWh from 16:00 to 24:00.