ES220204 theoretical test

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POWER PRODUCTION FROM RENEWABLE ENERGY AY 2021-22 4th February 2022 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. Consider a wind turbine installed on a site with a high roughness factor, that brings about a significant wind speed gradient across the area swept by the blades. Draw the velocity triangles at the tip for a blade respectively positioned at the top (vertical), middle (horizontal) and bottom (vertical) point of its path and and discuss the consequences for the turbine. 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 graphically evaluate the annual flow rate elabo- rated by the turbine. 4b. MECHANICAL AND MANAGEMENT ENGINEERING STUDENTS: Explain why biomass is of- ten considered nearly carbon neutral. Discuss the opportunity to exploit it in the…