ES210617 theoretical test

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POWER PRODUCTION FROM RENEWABLE ENERGY AY 2020-21 17th June 2021 Prof. Paolo Silva Time: 1 hour 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 blade has to be man- ufactured using a continuously variable pitch angle from the hub to the tip (the blade is said to be ‘twisted’). Due to the very high peripheral speed the blade can even be manufactured with a negative pitch angle at the tip: in this particular case please draw the velocity triangle at the tip and, considering an optimal incidence angle of 8°, give a numerical example (velocities and diameter) that will lead to a negative pitch angle. 2. Plot the lay -out of a geothermal direct steam cycle with 2 pressure laminations and draw the corresponding T-s diagram. Please highlight the main technical issues related to the plant op- eration. 3. Explain the definition of “grid parity” for a renewable power plant, distinguishing between the concept of grid parity in terms of price and cost. How can the growing share of electricity from renewables affect respectively the average cost of kWh and the balancing costs of the electric grid in a long-term perspective? 4a. ENERGY ENGINEERING STUDENTS: Considering a run- of-river plant based on a diversion channel, define the flow duration curve and show how it can be used to obtain a first design of the turbine. Please show how it is possible to graphicall y evaluate the annual flow rate elabo- rated by the turbine. 4b. MECHANICAL…