ES220621 test WHG

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Wind, Hydro and Geothermal Power Generation AY 2021-22 21st June 2022 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. Consider a large scale three-bladed horizontal axis wind turbine, designed to operate at stand- ard conditions (0 m a.s.l. and 15°C, corresponding to an air density of 1.225 kg/m 3). Provide a numerical example for a real machine, by assuming characteristic wind speeds and calculating the respective rotational speed and power output. Discuss the modifications you will make to the control system in order to operate the turbine at an altitude of 3000 m a.s.l. with an average ambient temperature of 5°C. How will the characteristic wind velocities and rotational speed change? (5 points) 2. Draw the temperature-heat diagram and the plant layout for a binary geothermal plant coupled to an Organic Rankine Cycle with 2 pressure levels. Number the points on both s chemes and discuss the importance of evaporation pressure on net electric efficiency and second law effi- ciency. (5 points) 3. Discuss the strategic importance of hydroelectric power plants with respect to the increasing dispatching requirements of the electricity grid. What is the role of different kinds of hydro plants in the electric system? (5 points) 4. Discuss the potential advantages of vertical axis wind turbine technology (VAWT) over the state of the art of three-bladed HAWT for off-shore applications. (5 points) Exercise (11 points) A run-of-river hydroelectric plant with a Kaplan…