ES230116 test WHG

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Wind, Hydro and Geothermal Power Generation (AY 2022-23) 16th January 2023 Prof. Paolo Silva Time: 90 minutes Instructions for the examination: 1) Clearly indicate your name on all the sheets you will deliver. 2) Give a synthetic and clear answer to as many questions as possible. The final score will be normalized according to the average results. 3) Talk with colleagues and / or cheating will cause the cancellation of the exam. 1. Considering a three-bladed horizontal axis wind turbine, explain why the pitch angle of the blade has to vary along the radius (the blade is said to be "twisted"). Draw the velocity triangles respectively at the hub, the average radius and the tip of the blade, graphically showing a situation where the pitch angle is zero. (5 points) 2. Plot the lay-out of a geothermal direct steam cycle with 2 lamination pressures and draw the correspond- ing T-s diagram. Compared to a cycle with 1 lamination pressure (with same thermodynamic conditions of the geothermal source), what are the differences in terms of scaling effects for the demister s and the turbine respectively, of turbine O&M costs, and plant auxiliary consumptions? (5 points) 3. What are the most promising technologies for floating off-shore wind turbines? Discuss advantages and disadvantages of the different technical solutions, also considering the construction phases and O&M issues. (5 points) 4. Consider a pumped -storage hydro power plant operating with a nominal head of 1 100 m and a given average head loss within the penstock of 44 m. Compute the “round trip efficiency” and the minimum energy price differential required to make the operation of the plant cost-effective. Illustrate the assump- tions made for the unknown parameters. (5 points) Exercise (11 points) A geothermal…