ES220114 theoretical test

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POWER PRODUCTION FROM RENEWABLE ENERGY AY 2021-22 14th January 2022 Prof. 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 manufactured 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 manufac- tured with a negative pitch angle at the tip: in this particular case please draw the velocity triangle at the tip. 2. Consider a direct geothermal plant exploiting a liquid-dominant source. Explain the reason why a lamination valve before the demister can be convenient by an energy point of view, despite the irreversibility introduced. 3. Classify biomass for energy applications and explain advantages and disadvantages in their exploitation, with particular reference to primary energy saving, avoided CO2 emissions and socio-economic aspects. 4a. For Energy and Mechanical Engineering students: What are the mismatch losses in a solar PV plant? Which measures can be taken to minimize them? 4b. For Management Engineering students: Provide a definition of the Energy Return on Investment (EROI) for a renewable power plant and discuss the opportunity to adopt the index to compare different technologies.