Question 1 (a) Figure Q.1 shows the general form of the annual wind speed distribution at a site where the mean wind speed is 5 metres per sec (5 m/s). This idealised curve is known as the Rayleigh distribution. i. Calculate the percentage of the year during which the site experiences light breezes (4 metres per second), moderate winds (7 metres per second) and strong winds (12 metres per second). (6 Marks) Sketch the Rayleigh curve of the site for a mean speed of 7.5 m/s [assume that the area under the new curve is the same as that shown in Figure Q.1] (5 Marks) ii. (b) The site owner has installed a two bladed HAWT (Horizontal Axis Wind Turbine) with a rotor diameter of 7 meters. For a wind speed of 12 metres per second the power output of the wind turbine is 15 KW. i. Calculate the efficiency of the turbine at this speed given that the density of the air is 1.23 Kg per cubic meter. (7 Marks) Compute the tip-speed ratio, if the blades are rotating at 240 rpm (revolutions per minute). (7 Marks) ii. 2000 1800- 1600 1400- 1200 hours per year for each speed band 1000 800- 600 400- 200 D 8 9 10 11 12 13 14 15 16 17 18 19 20 wind speedmetres per second Figure Q.1 Question 1 (a) Figure Q.1 shows the general form of the annual wind speed distribution at a site where the mean wind speed is 5 metres per sec (5 m/s). This idealised curve is known as the Rayleigh distribution. i. Calculate the percentage of the year during which the site experiences light breezes (4 metres per second), moderate winds (7 metres per second) and strong winds (12 metres per second). (6 Marks) Sketch the Rayleigh curve of the site for a mean speed of 7.5 m/s [assume that the area under the new curve is the same as that shown in Figure Q.1] (5 Marks) ii. (b) The site owner has installed a two bladed HAWT (Horizontal Axis Wind Turbine) with a rotor diameter of 7 meters. For a wind speed of 12 metres per second the power output of the wind turbine is 15 KW. i. Calculate the efficiency of the turbine at this speed given that the density of the air is 1.23 Kg per cubic meter. (7 Marks) Compute the tip-speed ratio, if the blades are rotating at 240 rpm (revolutions per minute). (7 Marks) ii. 2000 1800- 1600 1400- 1200 hours per year for each speed band 1000 800- 600 400- 200 D 8 9 10 11 12 13 14 15 16 17 18 19 20 wind speedmetres per second Figure Q.1