Energy Engineering - Solar and Biomass Power Generation

Full exam

SOLAR AND B I OMASS POWER GENERAT ION AY 2020-21 27 th Aug ust 2021 Prof. Giampaolo Manz olini Time: 90 minutes Instructions for the examination: 1) Clearly indicate y our surname and name on all the sheets y ou will deliv er. 2) The score refers to exercises done in a comprehensiv e manner with exact numerical results. Numerical results correct but not accompanied by expla- nations will not be tak en into account. The final score can be normalized according to the av erag e results. 3) Answer briefly and clearly only to the asked questions. Calculations and explanations which do not respond to the questions will not be considered for evaluation even if correct. 4) Talk ing with colleag ues and / or cheating will cause the cancellation of the exa m. 5) All the needed data for the resolution of exercises lies on this paper. I t is NO T ALLO WED to use material other than this (e. g. book s, clipboard etc. ). 6) Not all the prov ided inputs are necessary for the problem solv ing PV exercis e (16 po in ts) It is required to determine the mirror s urfac e area and the c onc entration ratio of a CPV s y s tem bas ed on two ax is trac k ing s ys tem with the following as sumptions (Question A: 3 points). Assumptions AC Power output [kW] 13 I nterception factor 0.95 D NI [W/m 2] 925 PV cell dimension [m 2] 0.60 D iffuse radiation [W/m 2] 100 D C/AC conversion efficiency 0.95 Reflectivity 0.94 PV efficiency @ actual condi- tions 0.1 5 Determine the energy c onvers ion los s es and the firs t law energy balanc e for the s olar c onvers ion into elec tricity (Ques tion B: 3 points ). Cons idering the heat trans fer properties and temperatures reported below, determine the PV cell temperature and the nominal PV c ell effic ienc y at STC temperature (Ques tion C: 5 points). Assumptions heat transfer coefficient (air -module surfa ce) [W/m 2K] 10 heat transfer coefficient (water coolant -module surface) [W/m 2K] 3500 coolant temperature variation [°C] 50 ambient temperature [°C] 20 coolant inlet temperature [°C] 25 power coefficient [W/°C] @ concen- trated radiation 80 Calc ulate the y early power generated as suming the following as sumptions (Question D: 4 points ): Assumptions Average Zenith angle [°] 30 Average Az imuth ang le [°] -6 D NI irradiance [kWh/m 2] 1650 Cell operating temperature [°C] 60 D iffuse irradiance [kWh/m 2] 350 Reflectivity reduction for dust deposition [%] 10 IAM (θ in degree) 1-1/cos(θ) Biomass exercise (14 points) A biomas s plant adopts wood pellets as fuel with the following c harac teristics: wood pellets % , weight dry bas is C 44. 10 H 8.44 O 47. 10 N 0.13 S 0.01 as h 0.22 LHV, k J/k g, dry basis 19100 Mois ture c ontent, % 10 Calc ulate the LHV and the HHV of the feeds toc k as received (∆h evapor ati on =2442,3 k J/k g) (Ques tion A: 2 points). Calc ulate the s toichiometric air flowrate for c ombus ting the biomas s (Question B: 3 points) The biomas s is gas ified as rec eived. Ass uming a c old gas efficiency of 72% (LHV s yng as / LHV fuel), a LHV power output of the s y ngas equal to 60 MW, and an air mass flow rate of 8.5 k g/ s, c alc ulate the air-to-fuel ratio of the gas ifier (Ques tion C: 3 points ). The s y ngas is c ompres sed by means of an elec tric al-driven c ompres s or (s tarting from ambient c onditions) and then us ed in a gas turbine c y c le with the following c haracteristic s: Ambient temperature [°C] 15 Compres s ion ratio 14 Ambient pres s ure [bar] 1 Air flowrate [k g/s ] 37 Turbine is entropic effic ienc y 90% Elec tric generator effic iency 97.5% Compres s or is entropic effic iency 84% Elec tric motor effic ienc y 95% Sy ngas c ompressor effic ienc y 78% Cp air [k J/k gK] 1.0 Gamma air 1.4 Cp c ombus tion produc ts [kJ/kgK] 1.15 Gamma c ombus tion products 1.35 Cp s y ngas [k J/kgK] 1.2 Gamma s y ngas 1.3 Calc ulate the net power output and the net elec tric effic ienc y (s tarting from both biomass and s y ngas) (question D: 6 points ).