Energy Engineering - Solar and Biomass Power Generation

Full exam

SOLAR AND BIOMASS POWER PRODUCTION AY 20 20 -21 15 th June 20 21 Prof. Giampaolo Manzolini Time: 90 minutes Instructions for the examination: 1) Clearly indicate your name on a ll the sheets you will deliver. 2) The score refers to exercises done in a comprehensive manner with exact numerical results. Numerical results correct but not accompanied by explanations will not be taken into account. The final score can be normalized ac cording to the average results. 3) Ans wer 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) Talking with colleagues and / or cheating will cause the cancellation of the exa m. 5) All the needed data for the resolution of e xercises lies on this paper. It i s NOT ALLOWED to use material other than this (e.g. books, clipboard etc.) . 6) Not all the provided inputs are necessary for the problem solving Exercise 1 (1 5 points) Calculate the LHV, HHV and the energy density of the biomass reported below on a “dry” and “as received” basis at the boiler inlet ( hevaporation = 2.44 MJ/kg) (3 points). Determine the biomass mass flowrate assuming that the net power output of the boiler is 50 MW, thermal losses from boiler walls are equal to 1% of the fuel LHV dry thermal input, un - burned carbon is 1.5 % (of carbon content, dry basis, LHV = 32.8 MJ/kg), stack temperature equal to 150°C (c p exhaust gases 1.1 kJ/kg K) and ashes melt at 900°C can be a ccounted as losses (equivalent heat capacity 2 kJ/kg K), ambient temperature is 15°C and the ( ������������������������ ������̇������������������ )̇ is equal to 9. ( 6 points) What would be the new boiler operating conditions boiler assuming a moisture content of the biomass equal to 30 %. Please calculate the new biomass flowrate and the efficiency both in LHV and HHV terms on as received base . (6 points) Keep the same assumptions from the previous point but for the new moisture content which should be summed up. Willow wood %, weight d ry basis C 47.5 H 6.0 O 40.0 N 0 S 0 Cl 1.0 Ash 5.0 LHV, kJ/kg, dry basis 18 300 Moisture content, % 13.0 Density (as received), kg/m 3 775 Exercise 2 (1 5 points ) Please design a PV plant for residential application and grid connected. The house consumes 5.25 MWh of electricity a year consists of a four -pitch roof with the shape and size reported in the following figure. The solar irradiance on horizontal plane is equal to 1 25 0 kWh/m 2. Assume that the electric balance between electricity purchased and sold to the grid is on annual base. Determine the number and configuration of the modules (P23L32 5) and inverters (select the one you consider more correct) to be installed: (5 points) What is the maximum power pro duced by the plant assuming the sun at solar noon on the summer solstice (45°09′23″N 10°47′28″E ) with a DNI of 8 25 W/m², a diffuse radiation equal to 75 W/m² and ambient tempera- ture of 3 2°C (4 points). How would the plant d esign change considering that the plant is off -grid? The solar radiation available on an average winter day together with the house consumptions is reported below. Determine the number of PV modules, inverters and the battery size in terms of capacity/powe r. (6 points) Hours Load W/Wp eak 1 0.2 0 2 0.2 0 3 0.2 0 4 0.2 0 5 0.2 0 6 0.6 0 7 1 0 8 0.9 0.1 9 0.3 0.2 10 0.3 0.3 11 0.5 0.4 12 0.7 0.5 13 0.6 0.4 14 0.3 0.3 15 0.2 0.2 16 0.2 0.2 17 0.7 0.1 18 0.8 0 19 1 0 20 1.4 0 21 1.3 0 22 1.1 0 23 0.8 0 24 0.7 0