UNIVERSITY OF BOLTON TW20 SCHOOL OF ENGINEERING B.ENG (HONS) ELECTRICAL & ELECTRONIC ENGINEERING EXAMINATION SEMESTER 2-2016/2017 RENEWABLE ENERGIES MODULE NO: EEE6006 Date: Monday 15 May 2017 Time: 2.00 4.00 INSTRUCTIONS TO CANDIDATES: There are Six questions. Answer ANY FOUR questions. All questions carry equal marks. Marks for parts of questions are shown in brackets. Electronic calculators may be used provided that data and program storage memory is cleared prior to the examination. CANDIDATES REQUIRE: Formula Sheet (attached).
Page 2 of 8 Q1 a) For a vertical wind turbine whose wind flow velocities vector diagram shown in figure 1 below, i) Write down the Vn and Vc equations. ii) Derive the mathematical relationship between the azimuthal angle and angle of attack of the blade. Assume no pitching. iii) The maximum angle of attack if tip speed ratio is 2.22. [8 marks] Fig.1 Wind flow velocities vector diagram Where v= ω.r the blade tip (tangential) speed vector; ω= the rotational speed of the rotor; R= the rotor radius; θ= the azimuth angle; Ulocal= local wind velocity vector; Ueff = the effective wind velocity vector; U = the undisturbed wind velocity vector; α= Angle of attack. Question 1 continued over the page
Page 3 of 8 Question 1 continued (b) A wind turbine whose blades are 15 metres in diameter, when the wind speed is 8 m/s, air density at sea level is 1.2 kg/m 3 and the maximum power coefficient for this turbine is 0.41. Determine: i) the sweep area of the turbine. [3 marks] ii) the output power of this turbine. Q2. A vertical-axis wind turbine has the following specifications: Nominal output power=50 kw, Turbine rotational speed=32.92 RPM, Gearbox ration=22.78, blade length = 6 m, rotor diameter= 16 m Permanent Magnet Synchronous Generator: star-connected, voltage= 400 V line to line, frequency= 50 Hz, phase winding inductance=1.89 mh, phase winding resistance=0.063ω, number of magnetic poles=8, generator efficiency=98%, gearbox efficiency=96.5%. Wind: wind density 1.2 kg/m 3, Determine: i) The mechanical power extracted from the wind. [3 marks] ii) The generator load angle. [9 marks] iii) The low-speed shaft torque. [3 marks] iv) The generator rotational speed. [3 marks] v) The quadrature-axis generator current per phase. [3 marks] vi) The wind speed in m/s if C turbine =0.43. Assume that the generator operates in parallel to the grid and generates no reactive power. Please turn the page
Page 4 of 8 Q3. (a) How is available energy in the wind related to the length of the blades in a wind turbine? (b) Why does the addition of an inverter or power electronic frequency converter allow a wind turbine to rotate at various speeds? (c) Explain what blade tip speed is and why it is important Q4. (d) Explain with the aid of diagrams briefly the function of a full converter that links a 3-phase permanent magnet synchronous generator to the grid of a wind turbine unit. [10 marks] (a) What are fuel cells? Providing a schematic of the Proton Exchange Membrane (PEM) fuel cell, describe the working of a H2/O2 fuel cell by providing the electrochemical reactions taking place at the anode and the cathode of the fuel cell. [10 marks] (b) Name the two proton conduction mechanisms seen in polymer electrolyte membrane and explain the difference between the two mechanisms. (c) Considering the power output of a fuel cell is function of the free energy used and the thermodynamics of the reaction, draw the electrical equivalent circuit of a fuel cell. [10 marks] Please turn the page
Page 5 of 8 Q5. (a) Assuming the calorific value of H2 as 11.92 kj/m 3, determine the efficiency of a typical fuel cell which is supplying a current of 1A at voltage of 0.65V over a period of 180s? During this process, 23 ml of H2 is being consumed. [8 marks] (b) Explain the principle of a p/n junction and how the solar cell works. (c) Draw a typical IV curve for a solar cell in dark and under illumination, and explain what is the Voc, Isc, fill-factor and efficiency in the IV figure. (d) Explain how a parasitic resistance could affect the efficiency of a solar cell. Explain both the parasitic resistance in series and in parallel. (e) Make a list of possible methods to improve the efficiency of a solar cell. Please turn the page
Page 6 of 8 Q6 Design a solar panel system for a house use. The house has a 24V nominal operating voltage supplied by solar panel powered batteries. The total power usage for the house is 10000 Wh/day. The electricity price is 0.3/kWh. Average sunlight is 6hours/day. Solar module on market is rated at a peak power of 144Wp, voltage of 36V and current of 4.0A. The price for a PV module is 150. Battery on market is rated at 24V, 12Ah, and only 85% of the power can be used. Battery reserve time is 2 days. The price for each battery is 28. The inverter efficiency is 95%. The installation of PV panels and all other materials for PV panel installation is 1000. (a) Draw the configuration of the solar system for application, and name each component and their function. (b) How many PV modules are needed to meet the requirement of the house use? [7 marks] (c) How many batteries are needed to meet the requirement of the house use? [7 marks] (d) How many years can the investment get paid back? (e) If it is grid-tie solar panel, how many years can the investment get paid back? [2 marks] End of Questions
Page 7 of 8 Formula sheet These equations are given to save short term memorisation of details of derived equations and are given without any explanation or definition of symbols; the student is expected to know the meanings and usage. Fuel Cell Wind Turbine S = c H S a = R L ω = ρr2 (SC t SC d 1 4 S ac da ) c+iθ λ = ωr U, α = tan 1 ( sinθ cosθ+λ ) C t = C L sinα C d cosα T= F T. 2R= 1 ρc 2 t ARU 2 Pwind = ω. T C p = C t. λ R W = U 1 + 2λcosθ + λ 2 F T = 1 ρsc 2 tw 2 F T avg = 1 2π 2π 0 F τ(θ) dθ Permanent Magnet Synchronous machine
Page 8 of 8 J g dω r dt = T g T d T e V = v d 2 + v q 2 I = i d 2 + i q 2,,