Energy Engineering - Power Production from Renewable Energy

Multiple choice test

POWER PRODUCTION FROM RENEWABLE ENERGY AY 2023-24 17 th June 2024 Prof. Andrea Giostri Time: 1 hour NAME and SURNAME:.................................................................................................................................................. COURSE and CFU:......................................................................................................................................................... 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. OPEN QUESTIONS (points 18) 1. For All students: Express the energy of a photon as a function of the wavelength and plot its trend. Referring to this plot, discuss the theoretical limit for a single junction cell and discuss the choice of cell material. How this limit could be improved with a multi-junction cell? 2a. For Mechanical Engineering students and Management Engineering students (5CFU): Discuss the effect of a thermal storage system on the LCOE for a CSP plant. Consider also the impact of solar multiple on LCOE. 2b. For Energy Engineering students and Management Engineering students (8CFU): Consider having a geothermal well with liquid geothermal fluid at 130°C and 20 bar. Choose the best solution that, in your opinion, allows producing electricity exploiting this resource. Draw the layout and discuss the main characteristics of the plant. MULTIPLE-CHOICE QUESTIONS (points 12) Answer to the following 15 questions. Select the box with correct answer (0.8 points if correct, -0.3 points if wrong). For a Horizontal Axis Wind Turbines ( rated power capacity equal to 3 MW): v Undisturbed wind speed The available power of the wind is proportional to v3 Blades are twisted in order to have the same relative velocity along the blade Cp decreases for wind speed higher than Vrated  true  true  true  false  false  false Considering different control strategies for a wind turbine: ωRotational speed In variable pitch control the angle of attack is decreased if wind speed increases Passive stall is obtained changing the pitch angle For wind speed between Vcut-in and Vrated, the ω is kept constant and pitch is changed  true  true  true  false  false  false Consider a PV cell : “sc”  Short circuit “oc”  Open circuit MP  Maximum point Fill factor is defined as the ratio between real power output and the product between Vsc and Ioc If Tcell increases, V MP decreases Considering the simplified equivalent circuit, shunt resistance is higher than series resistance  true  true  true  false  false  false For Mechanical and Ener gy students Consider energy conversion of biomass: HRT  Hydraulic Residence Time In anaerobic digestion, high HRT impl ies an increase of biogas production per unit of feedstock Production rate as function of residence time shows a maximum Biomass-fired steam cycle is commonly characterized by small-scale and Tmax similar to coal power plants  true  true  true  false  false  false For Mechanical and Management students ( 5 CFU) Consider two technologies (A, B) based on different renewable sources: CCA  “Cost of CO 2 avoided” heq  Equivalent hours TES  Thermal Energy Storage If LCOE A