UNIVERSITY OF BOLTON RAK ACADEMIC CENTRE BENG (HONS) ELECTRICAL AND ELECTRONIC ENGINEERING SEMESTER ONE EXAMINATION 2017/2018 RENEWABLE ENERGIES

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1 UNIVERSITY OF BOLTON OCD029 RAK ACADEMIC CENTRE BENG (HONS) ELECTRICAL AND ELECTRONIC ENGINEERING SEMESTER ONE EXAMINATION 2017/2018 RENEWABLE ENERGIES MODULE NO: EEE6006 Date: Saturday 13 th January 2018 Time: 2:00pm 4:00pm INSTRUCTIONS TO CANDIDATES: There are 5 questions. Answer any 4 questions. All questions carry equal marks. Marks for parts of questions are shown in brackets.

2 Page 2 of 10 Q1. (a) Explain how current is generated in a photovoltaic cell and discuss the VI characteristics using a schematic diagram. (b) Design a PV system for a house in UAE having 20, 100W light bulbs which need to remain powered for 6 hours a day. Use 1605mm x 909 mm, 240W Polycrystalline Apex rectangular rigid solar panel (5.5 AED/W) for meeting the energy requirement. (10 marks) (c) Evaluate the average yearly energy yield and performance ratio for a polycrystalline 160W PV module. Given Derating due to dirt : 5% Derating modules Manufacturers : 5% Derating temperature : 15% Ambient temperature : 30 o C DC cable loss : 3% AC cables : 1% Inverter efficiency : 96% Average annual solar radiation : 2285 kwh/m 2 (4 marks) (d) Compare and contrast different solar cell technologies. (6 marks) Total 25 marks Please turn the page

3 Page 3 of 10 Q2. (a) Explain how fuel cells are classified based on i. Temperature of Operation (3 marks) ii. Types of fuel iii. Chemical Nature of the Electrolyte (3 marks) (3 marks) (b) Using a schematic diagram discuss the construction and working principle of Proton Exchange Membrane fuel cell (PEMFC). (c) A fuel cell employs the reaction below, A + B AB. Given that for each molecule of AB, 2 electrons circulate in the load. Table 2.c shows the relevant thermodynamic data at STP Enthalpy of formation kj/k mole MJ/kmole A(g) B(g) AB(g) Table 2.c Thermodynamic data Determine the reversible voltage generated by the fuel cell. (d) Consider an electrolyzer in which there are 250 series connected cells each one having the below characteristics, V = x I, operating at 20,000 A. Determine the following i. The total voltage that must be applied. ii. The hydrogen production rate in kg / day. iii. The rate of water consumption in m 3 / day. iv. The heat power rejected. (1 mark) (1 mark) Total 25 marks

4 Page 4 of 10 Q3. Please turn the page The V -I characteristic of a Hydrogen/Oxygen fuel cell operating at RTP is Vl = I. This fuel cell battery must supply 100 kw of power (needed only for acceleration) for an automobile. The maximum internal heat dissipation capability is 300W. Product water exits the cell in vapour form. The fuel cells deliver their energy to an inverter. The efficiency of this unit can be taken as 100%. Analyze the following a) The voltage that the fuel cell battery (at 100 kw), must deliver assuming the smallest possible number of individual cells are used. (10 marks) b) Determine the efficiency of the cell. c) If cruising at 110 km/h need only 20 kw, estimate in kilogram the amount of hydrogen required to cover a range of 800 km. (10 marks) d) If the hydrogen is stored at 500 atmospheres, how much volume does it occupy at 298 K? (3 marks) Total 25 marks Please turn the page

5 Page 5 of 10 Q4. a) Compare and contrast Vertical Axis Wind Turbine (VAWT) and Horizontal Axis Wind Turbine (HAWT) b) Analyse the optimization of angle of attack on HAWT blade design. c) Explain tip speed ratio of a HAWT. d) A Suzlon S.66/ MW wind turbine operating at an average wind speed of 8 m/s has rotor diameter of 66 m and rotational speed of rpm. The capital cost of installation is estimated as AED 3000/kW with a payment of a fixed charge rate of 15% excluding annual Operation and maintenance cost of 2% of initial installation cost. Assume air density = kg/m 3 i) Evaluate the range of tip speed ratio and find the number of blades in the turbine (3 marks) ii) Evaluate the capacity factor of the turbine using Rayleigh wind statistics. iii) Find the annual energy production and the cost of energy (COE). (3 marks) iv) Determine the change in power produced by the turbine when there is a 50% increase in wind speed Total 25 marks Please turn the page

6 Page 6 of 10 Q5. a) Discuss the aerodynamic operation of Wind Turbines. (6 marks) b) Analyse the role of thrust, torque and solidity in the design of wind turbine rotor. (6 marks) c) A 40m diameter wind turbine having blade tip speed ratio of 5.0 is placed at a hub height of 50m in a terrain having a few trees. The wind speed at a height of 10 m in the chosen terrain is 9.5 m/s, air density is kg/m 3 and surface roughness length is 100mm. i) Calculate the velocity of wind at the given hub height. ii) Find the ratio of available power in the wind at the highest point the rotor reaches to its lower point if power law co-efficient is 0.2. iii) Determine the rotational speed of the rotor. If the generator turns at 1500 rpm, what gear ratio is needed to match the rotor speed to the generator speed? (4 marks) iv) Evaluate the power produced by the turbine if the power co-efficient is 0.30 and the value for torque co-efficient and thus the torque available at the rotor shaft. Total 25 marks END OF QUESTIONS

7 Page 7 of 10 Average yearly energy yield EQUATION SHEET Esys = Parray_STC x ƒman x ƒdirt x ƒtemp x Htilt x η pv_inv x η inv x ηinv_sb Performance Ratio Eideal = P array_ STC x Htilt STP (Standard Temperature Pressure) : 1 atmosphere, K RTP (Reference Temperature Pressure) : 1 atmosphere, K Heat generation (Second law of thermodynamics): Free Energy: Reversible Voltage : where is enthalpy of formation, is Entropy is temperature q=1.6 x N0=6.023 x Hydrogen production rate: 1 H2 is equal to 202 x Kg/mol

8 Page 8 of 10 Equations for Wind Energy Efficiency = Power output/ Powerinput Powerturbine =Cp x Pwind (Cp= power coefficient Pwind=ρAV 3 /2, ρ-air density in kg/m 3 A =area swept by rotor in m 2 V-velocity of wind in m/s Tip speed ratio, λ = ωr/v = 4π/n ω- angular velocity in rad/s R- rotor radius in m V- velocity of wind in m/s n- no: of blades in the turbine

9 Page 9 of 10 Cp/CT= λ (CT=Torque co-efficient) CT=Tturbine/Tmax Tturbine- torque available at rotor shaft Tmax=ρAV 2 R/2 Cp=[0.087*V (PR/D 2 )] Cp capacity factor or power co-efficient V- velocity of wind in m/s PR- rated power in KW D-rotor diameter m COE = (CC*FCR + Co&M) / (Cp*Ea) COE- cost of energy CC-installed capital cost, FCR Fixed Charge rate Co&M Operation & Maintenance cost Ea- Annual Energy production in KWh U(Z)/U(ZR) =[ ln (Z/Zo) ]/ [ ln (ZR /Zo)] U(Z)/U(ZR) = (Z/ZR) α U(Z) = unknown velocity (m/s) at height Z in m. U(ZR) = Known velocity (m/s) at reference height ZR in m Zo = surface roughness length in m. α = power law co-efficient Gearbox ratio = generator speed in rpm/ rotor speed in rpm

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