(a) Draw a representative power curve of a commercial turbine and explain its main characteristics (i.e. phenomena resulting in its typical shape, use illustrations where helpful). Proceed to superimpose a 2nd curve on your graph representing the total power available in the wind and explain with the aid of relevant theory/other limitations why this differs from the turbines power curve. [8] (b) (c) Describe what is meant by the optimum tip speed ratio, Aopt, of a wind turbine and derive the expression shown below for its calculation. Draw a suitably labelled schematic illustrating the variables of interest in your derivation and explain the logic followed. 2opt = 4/n [10] Find the Roman numeral classification of a wind turbine required at a site where the gust wind speeds noted in the table below were observed from long standing measurements. Relevant equations are provided at end of exam script. [15] Hint: Either graphical or a numerical methods can be used to solve this problem. You may use either. Annual Gust Wind No. of Annual Gust Wind No. of Occurrences over Occurrences over Speed at 10m (m/s) Speed at 10m (m/s) 70 year period 70 year period 12-14 0 24-26 14-16 2 26-28 16-18 6 28-30 18-20 16 30-32 20-22 17 32-34 22-24 10 34- 0 Table 3.1 Number of occurrences of maximum annual gust wind speeds over a 70 year period 8 4 3 2 2