Sustainable Energy Workshop Palestine Polytechnic University May 10 -13 2010 Hebron, Palestine
Day Two Agenda Tuesday, 11/05/2010 09: 00 - 10: 45 Presentation: Wind Energy Systems 10: 45 - 11: 00 Coffee Break 11: 00 – 12: 00 Discussion: Wind Energy Systems 12: 00 - 13: 00 MATHWORK SIMULATION 13: 00 - 14: 00 Lunch Break 14: 00 - 15: 15 Using Computer Simulation for Solar Energy System Design 15: 15 - 15: 30 Coffee Break 15: 30 - 17: 00 Wind Energy “Hands on” Training 14: 00 – 14: 30 Panel Discussion: “AC vs. DC” 14: 30 - 15: 30 Closing Session
Day Two Agenda (detailed) Tuesday, 11/05/2010 09: 00 - 10: 45 Presentation: Wind Energy Systems : 1 - Wind Energy (90 min) 10: 45 - 11: 00 Coffee Break 11: 00 – 12: 00 Discussion: Wind Energy Systems : 2 - Key questions and debate (60 min) 12: 00 - 13: 00 Mathematical Analysis of Wind Energy Systems 3 - Mathwork presentation (60 min) 13: 00 - 14: 00 Lunch Break 14: 00 - 15: 15 Using Computer Simulation for Solar Energy System Design 15: 15 - 15: 30 Coffee Break 15: 30 - 17: 00 Wind Energy “Hands on” Training 14: 00 – 14: 30 Panel Discussion: “AC vs. DC” 14: 30 - 15: 30 Closing Session Sustainable Energy Resources- PESPRU 3
Sameer Khader Associate Professor, Ph. D, EE, Visiting professor- University of Hartford, Connecticut, USA Department of Electrical and Computer Engineering College of Engineering and Technology Palestine Polytechnic University (PPU) ACKNOWLEDGMENT The instructor would like to thank the Open Society Institute (OSI), and USAIDAMEDEAST for fully sponsoring the visit to university of Hartford according to Palestinian Faculty Development Project ( PFDP). ACKNOWLEDGMENT The instructor would like to thank Hartford university administration and Prof. Cay Yavuzturk / university of Hartford for his valuable lectures in this field , and support. 4
OUTLINE ALTERNATIVE CLEAN ENERGY RENEWABLE ENERGY CONSUMPTION WIND ENERGY GROWTH ENERGY COST & PRESPECTIVES SUMMARY
ALTERNATIVE CLEAN ENERGY Wind Solar, Tide and Wave Hydroelectric Biomass and Waste The total energy generated by renewable resources by 2008 was: 3472. 70261 Billion k. Whr Sustainable Energy Resources- PESPRU 6 6
Wind Energy What is the cause of the wind: Differences in atmospheric pressure due to differences in temperature are the main cause of wind. Because warm air rises, when air fronts of different temperatures come in contact, the warmer air rises over the colder air, causing the wind to blow. Wind generators take advantage of the power of wind. Long blades, or "rotors", catch the wind and spin. Like in hydroelectric systems, the spinning movement is transformed into electrical energy by a generator. The placement, or "siting" of wind systems is extremely important. In order for a wind-powered system to be effective, a relatively consistent wind-flow is required. Obstructions such as trees or hills can interfere with the rotors. 7
Wind Energy Cont’d There are certain minimal speeds at which the wind needs to blow. For small turbines it is 13 Km/hr ( 3. 6 m/s). Large plants require speeds of 20 Km/hr ( 5. 6 m/s). Problems : One of the main problems with wind power is the space that is used up by the so-called "wind farms. " In some cases, the space taken up can seriously alter the environment. The good news is that although wind farms require a great deal of square mileage, there is quite a bit of space between the actual wind machines. This space can be used for agricultural purposes. Another problem with wind power is that relatively speaking, it does not generate very much energy for the price. Perhaps this setback is made up for in friendliness to the environment. Sustainable Energy Resources- PESPRU 8
RENEWABLE ENERGY CONSUMPTION , 2008 http: //en. wikipedia. org/wiki/World_energy_resources_and_consumption Sustainable Energy Resources- PESPRU 9
RENEWABLE ENERGY CONSUMPTION , …cont’d Renewable Energy at the end of 2008 compared with other resources. http: //www. eia. doe. gov Sustainable Energy Resources- PESPRU 10
WIND ENERGY GROWTH The energy harvested form the wind has stable growth. For example in 2007 it was ~35 Billion Kilowatt-hours. Sustainable Energy Resources- PESPRU 11 11
WIND ENERGY GROWTH, …cont’d Sustainable Energy Resources- PESPRU 12
ENERGY COST & PRESPECTIVES The cost of PV energy by the year of 2010 is expected to drop to 47 $/MWhr Sustainable Energy Resources- PESPRU 13
ENERGY COST & PRESPECTIVES……cont’d Electricity Generation Costs ~~ , ¢/k. Wh Combined cycle gas turbine 3 -5 Wind 4 -7 Biomass gasification 7 -9 Remote diesel generation 20 -40 Solar PV central station 20 -30 Solar PV distributed 20 -50¢/k. Wh Despite the highest cost of 1 k. Whr energy extracted by the solar irradiation, this source is the most sustainable and its energy cost continues to drop down due to high investment rate, strategic support, and world wide cooperation in this sector. When the environmental and social costs of power generation are considered, the economics of solar electricity becomes attractive. Sustainable Energy Resources- PESPRU 14
SUMMARY One day fossil resources will be over , and we must prepare economy, industry, and community to invest in the infinity clean and friendly to the environment resources. Sustainable Energy Resources- PESPRU 15
Presentation#2 : WIND ENERGY Ancient Resource Meets 21 st Century 16
Presentation#2 : INTRODUCTION TO WIND ENERGY Wind Turbines, Power for a House and City 17
Wind Energy Outline INTRODUCTION TO WIND ENERGY HISTORICAL PREVIEW TYPES AND CLASSIFICATIONS WIND TURBINE CONSTUCTION POWER IN THE WIND/MODELING WEIBULL DISTRIBUTION WIND TURBINE OPERATION WIND FARMS WIND ENERGY CHALENGES WIND FARMS ECONOMICS CONCLUSION 18 Sustainable Energy Resources- PESPRU 18
INTRODUCTION TO WIND ENERGY CAUSE : Difference in temperatures Difference in atmospheric pressure Wind Blowing Warm air front Eventually tornados Cold air front When air fronts of different temperatures come in contact, resulting different air pressure, …. Wind blowing
Wind Turbine Description
HISTORICAL PREVIEW • n n n n 1 A. D. Hero of Alexandria uses a wind machine to power an organ and moving tools. ~ 400 A. D. Wind driven Buddhist prayer wheels 1200 to 1850 Golden era of windmills in western Europe – 50, 000 : 9, 000 in Holland; 10, 000 in England; 18, 000 in Germany 1850’s Multiblade turbines for water pumping made and marketed in U. S. 1882 Thomas Edison commissions first commercial electric generating stations in NYC and London 1900 Competition from alternative energy sources reduces windmill population to fewer than 10, 000 1850 – 1930 Heyday ( peak production) of the small multi blade turbines in the US Midwest as many as 6, 000 units installed 1936+ US Rural Electrification Administration extends the grid to most formerly isolated rural sites and grid electricity rapidly displaces multi blade turbine uses.
TYPES AND CLASSIFICATIONS Turbines can be categorized into two overarching classes based on the orientation of the rotor Vertical Axis Horizontal Axis
TYPES AND CLASSIFICATIONS Ø Vertical axis wind turbines - have their axis of rotation vertical to the ground almost perpendicular to the wind direction. - can receive wind from any direction; therefore complicated yaw device can be eliminated. - have generator and the gearbox are housed at the ground, which make the tower design simple and more economical. - have ground level maintenance. - have no need of pitch control when used for synchronous applications. ØAlso there a lot of disadvantages: • They are not self-starting, additional mechanism may be required to push and start the turbine. • Guy wipes are required to support the tower structure which may pose some practical difficulties.
TYPES AND CLASSIFICATIONS Ø Horizontal axis wind turbines - have their axis of rotation horizontal to the ground almost parallel to the wind stream. - most of the commercial wind turbines fall under this category. Ø This type machines has some distinct advantages • low cut-in wind speed • easy furling ( rotating) and manufacturing. • they have high power coefficient, which make them good advantage in design of large power plants. Ø Also there a lot of disadvantages: • they have complicated and expensive design because of the generator and the gearbox are placed over the tower in the nacelle. • the need for tail (yaw) drive to orient the turbine towards turbine.
HORIZONTAL WIND TURBINE CLASSIFICATIONS Horizontal WT can be classified into three types : • Single blade; • Two blades • Three blades • Multi blades These turbines are characterized with high power coefficient and extended extracted power range, but needs high advanced ratio ( high wind speed). Single and two-blades are rarely used due to the need of counter weight. Threeblades turbine are mostly used and commercially available. 25
VERTICAL WIND TURBINE CLASSIFICATIONS Vertical WT can be classified into three types : • Darrieus • Savonius • Musgrove These turbines are characterized with low Power coefficient and limited extracted power, but in the mean time have with low advanced ratio ( low wind speed), which is good indicator. 26
Number of Blades – One • Rotor must move more rapidly to capture same amount of wind – – – • • Gearbox ratio reduced Added weight of counterbalance negates some benefits of lighter design Higher speed means more noise, visual, and wildlife impacts Blades easier to install because entire rotor can be assembled on ground Captures 10% less energy than two blade design Ultimately provide no cost savings. Has not accepted visual form. 27
Number of Blades - Two n n Advantages & disadvantages similar to one blade turbine. Need teetering (balancing) hub and or shock absorbers because of gyroscopic imbalances Capture 5% less energy than three blade designs. Generate additional vibrations &noises. 28
Number of Blades - Three n n Balance of gyroscopic forces Slower rotation n increases gearbox & transmission costs n More aesthetic ( nice view), less noise, fewer bird strikes. 29
WIND TURBINE CONSTUCTION 30
WIND TURBINE CONSTUCTION …cont’d 31
FUNCTIONS OF WIND TURBINE PARTS The Nacelle: this is the machine corpus mounted on the tower, and contains all the machine elements. Rotor: this is, three-blades ( may more or less) diameter that swept in the air. Blades; are made from light material with pitch angle. The pitch mechanism on the blades adjusts the angle of the blades to be in the wind direction and to maximize the extracted power. Low- speed shaft: this is a steel shaft connected with the plate, rotates at low speed with high torque, and transmit the speed to the next stage (high speed stage). Gear box: change the speed form low rate to the high rate values ( high speed) suitable for the electrical generator operation. High-speed shaft: used to rotate the generator at high speed with purpose to generate the required voltage and electrical frequency. 32
FUNCTIONS OF WIND TURBINE PARTS, . . cont’d Generator: This either DC or AC generator that converts the input mechanical power in terms of torque and speed into output electrical power in terms of voltage and current ( electrical energy). Brake: this an electromechanical system that acts on the low-speed shaft with purpose braking the turbine in emergency case or when the speed falls below the cut-in value or raised up above the cut-out value. Yaw drive and Yaw motor: are used to keep the plane of the blades oriented into the wind. Anemometer: wind measurement device used to measure the speed value and direction. Wind vane: used to direct the nacelle toward the wind direction. Tower: this a cement construction used to carry on all the equipments 33
WIND TURBINE CONSTUCTION and MATERIALS Wood n n n Strong, light weight, cheap, abundant, flexible Popular on do-it yourself turbines Solid plank Laminates Veneers Composites
Blade Composition Metal n Steel n n Heavy & expensive Aluminum n n n Lighter-weight and easy to work with Expensive Subject to metal fatigue 35
Blade Construction Fiberglass n n Light weight, strong, inexpensive, good fatigue characteristics Variety of manufacturing processes n n n Cloth over frame Filament winding to produce spars Most modern large turbines use fiberglass 36
Large Wind Turbines n n n n 450 ft ( 130 m)base to blade Each blade 112 ft (35 m) Span greater than Booing 747 163 tons total weight Foundation 20 feet deep (7 m) Rated at 1. 5 – 5 megawatt Supply at least 350 homes 37
Wind Turbine Montage 38
Rotor Solidity is the ratio of total rotor plan - form area to total swept area Low solidity (0. 10) = high speed, low torque R a A High solidity (>0. 80) = low speed, high torque Solidity = 3 a/A
POWER IN THE WIND / MODELING Power= 1/2 x air density x swept rotor area x (wind speed)3 A V 3 Density = P/(Rx. T) P - pressure (Pa) R - specific gas constant (287 J/kg. K) T - air temperature (K) kg/m 3 Area = r 2 m 2 Instantaneous Speed (not mean speed) m/s Where : Swept Area: A = πR 2 Area of the circle swept by the rotor (m 2). R
POWER IN THE WIND / MODELING, …cont’d Power in the Wind = ½ρAV 3 This power depends on : – The swept area, A – Wind speed, V ( cube of this speed) – Air density, R R 41
POWER IN THE WIND / MODELING, n Wind Speed n n …cont’d Wind energy increases with the cube of the wind speed 10% increase in wind speed translates into 30% more electricity Twice time increase in the wind speed translates into eight time increase in the generated electricity Height n n Wind energy increases with height to the 1/7 power Twice time the height translates into 10. 4% more electricity, because as the tower high increases the cold air has high density, and it help in moving the blades. 42
POWER IN THE WIND / MODELING, n Air density n n …cont’d Wind energy increases proportionally with air density Humid climates have greater air density than dry climates Lower elevations have greater air density than higher elevations Blade swept area n Wind energy increases proportionally with swept area of the blades n n n Blades are shaped like airplane wings 10% increase in swept diameter translates into 21% greater swept area Longest blades up to 413 feet in diameter n Resulting in 600 foot (200 m) total height 43
POWER IN THE WIND / MODELING, n The Lift Force is perpendicular to the direction of motion. We want to make this force BIG. …cont’d α= low α = medium <10 degrees n The Drag Force is parallel to the direction of motion. We want to make this force small. α = High Stall!! 44
Airfoil Shape Just like the wings of an airplane, wind turbine blades use the airfoil shape to create lift and maximize efficiency. 45
Twist & Taper n n n Speed through the air of a point on the blade changes with distance from hub Therefore, tip speed ratio varies as well To optimize angle of attack all along blade, it must twist from root to tip Fastest Faster Fast 46
Tip-Speed Ratio ΩR Tip-speed ratio is the ratio of the speed of the rotating blade tip to the speed of the free stream wind. There is an optimum angle of attack which creates the highest lift to drag ratio. Because angle of attack is dependant on wind speed, there is an optimum tip-speed ratio R ΩR TSR = Where, V Ω = rotational speed in radians /sec R = Rotor Radius V = Wind “Free Stream” Velocity 47
a n sf er Betz Theory : re d e n According to Albert Betz / German Scientist, 1928 theorem, the question is : er g How much available and reasonable power can be extract from wind turbine y with concrete design ? . ta The Betz analysis uses an actuator disk approach. k e s pl a c e in And this energy transferred th takes place upstream and e pl downstream of the actuator 48
Actuator Disk Analysis This Analysis depicted three distributions : PRESURE VELOCITY CROSS-SECTION 49
Pressure and velocity variations High pressure at P 1 & P 2 Wind stream Output velocity Input wind velocity Cross-section distribution 50
MATHEMATICAL MODELING 1. The actuator disk is represented by blades in the pressure and velocity distribution, and by a dotted line in the cross sectional area distribution. The actuator area is the area swept by the blades and equal to πD²/4, where D is the blade diameter. 2. The change in the kinetic energy E is : Where Ve, and Vo are the incoming and out-coming from the blades speed respectively. 3. The flow -rate mass of the stream air is given at ambient temperature is : 51
MATHEMATICAL MODELING …. Cont’d 4. The output velocity( leaving the blades velocity) is : According to Betz theory a=b/2 where ( a and b are integers with certain value). 5. Taking into account the up mentioned equations for the energy ca be express as follows: Hence, the changing in kinetic energy due to moving the air from the upstream point to downstream point has a maximum value with respect to a, and can be found by setting the first derivative to zero. 52
MATHEMATICAL MODELING …. Cont’d 6. We found that E=max at a=1/3, therefore the actual speed that extract energy is This means that the approaching (striking) to the actuator (blades) wind speed is decreased by 1/3 of its stream value (coming value). 7. The maximum available power is calculated as follows: 8. The maximum power coefficient can be determined as follow: 53
MATHEMATICAL MODELING …. Cont’d Which means that, the power extracted from the wind turbine theoretically according to Bitz approach can not exceed 59. 26% of the available. 54
Therefore, as a summary from Betz approach is : - All wind power cannot be captured by rotor. . - Theoretical limit of rotor efficiency is 59% - Most modern wind turbines have CP in the 35 – 45% range 55
MATHEMATICAL MODELING …. Cont’d 9. The advanced or tip ratio: This is the ratio between the rotor speed and wind velocity, tip ratio can be determined as follow: Where, =2. . n/60, and n=120. f/p; p- is number of poles of the generator. 10. The rotor torque : This is the mechanical torque acting on the rotor shaft, and can be given by : Depending on the rotor construction ( number of blades), the TCR differs from one wind turbine to another, and according to this ratio, the wind turbine configuration can be select. 56
MATHEMATICAL MODELING …. Cont’d EXAMPLE PROBLEM : Imagine there is a geographical location where you want to install a wind turbine with data: Wind velocity Ve=40 km/hr ( which is 11. 11 m/s); Atmosphere pressure 101. 3 k. Pa, the wind temperature is 20 C, Blade diameter ( Rotor swept diameter Da=10 m). • What is the maximum available power, Pavailable=? • What can be the maximum extracted power Pextract =? • What is the reasonable power Presonable=? • What is the rotor speed and torque . 57
Example Problem#1 Solution: The solution will be listed in five steps as follows: Step#1: The available power , Pavailable=? The Atmosphere pressure for the temperature of 20°C is given to be around ρa=1. 204 kg/m 3, hence, the available power is = Pavailable=64. 86 k. W. 58
Example Problem#1……cont’d Step#2: The available extracted power , Pextracted=? Step#3: The reasonable power, Presonable=? The reasonable power means the actual power that can be extracted for a given TCR and rotor configuration. This could be found by looking over the relationship between the TCR and number of rotor blades shown on the next slide figure. For (two blades) at maximum Cp=0. 46, we pick the value of tip ratio =11. Therefore the reasonable power is : The reasonable power is : 29. 4 k. W 59
Example Problem#1 ……cont’d For =11; Cpmax=0. 46 60
Example Problem#1 ……cont’d Step#4: The rotor speed and torque: Taking into account that the tip ratio is 11, and the diameter is 10 m the rotor speed is : Therefore, the rotor blades will rotates at speed of 233 rpm, and with acting on the shaft torque of 1221. 3 N. m. Now depending on the frequency and speed ratio of the gearbox, the generator speed and configuration is selected ( number of of poles, power, frequency……) 61
WIND ENERGY RESOURCES AND WEIBULL DISTRIBUTION Wind Energy Resources Now, the question is: Is it efficient to montage/build the wind turbine system everywhere without any restrictions? 62
WIND ENERGY RESOURCES…cont’d The answer is: No !, Why ? , … because : 1. Wind velocity varies from one site to another, and this called wind distribution or known as “ Wind Energy Resource Atlas” , 2. Most of the Nations/ Countries have their own National Renewable Energy Labs (NREL). For example the United States NREL has the site www. nrel. gov, that gives the designer overall description and statistics about the regions and sites where the wind energy is harvesting. 3. A unique feature is an assessment of the "CERTAINTY " of the wind data. The wind data ( wind density) are rated from 1( lowest degree) to 4(the highest degree) of the certainty. The coming figure illustrates the wind density distribution of USA. 63
WIND ENERGY RESOURCES…cont’d Locations with high energy harvesting feasibility Wind Atlas of USA Locations with weak energy harvesting feasibility 64
WIND ENERGY RESOURCES…cont’d What is the wind power density ? This is the available average wind power per meter square of wind turbine area. The Wind Power Density Classes: The wind power density(WPD) is measured from class 1(lowest) to class 7(highest) and is specified at nominal 10 m and 50 m elevations, as follows: Wind Power Classes Elevation , 10 m Elevation, 50 m WPD ( W/m 2) Wind Speed (m/s) 0 0 0 1 100 4. 4 200 5. 6 2 150 5. 1 300 6. 4 3 200 5. 6 400 7. 0 4 250 6. 0 500 7. 5 5 6 300 400 6. 4 7. 0 600 8. 8 7 1000 9. 4 1000 11. 9 65
WIBULL DISTRIBUTION Statistics of Wind Energy Resources Several statistical methods are used to predetermine the harvesting places and sites for wind power energy. One of these statistical methods is called Weibull distribution, which states that the occurrence of a given wind speed over a year can be expressed by the following distribution: Where c is a scale parameter , k is a shape parameter, and v is the wind velocity. 66
WIBULL DISTRIBUTION……cont’d The shape parameter controls the shape of the distribution; the large the shape parameter, the closer to distribution comes to being Gaussian distribution. While the scale parameters controls the value of the mode (most probably wind speed). The larger the scale parameter, the higher the mode and the lower the probability of a given speed less that the mode. The shape parameter is dimensionless, while the scale parameter must have the same unit as the speed. Usually for wind turbines the shape parameter is taken to be k=2, because it provides a generally acceptable match for the wind speed distribution at most sites. 67
WIBULL DISTRIBUTION……cont’d 68
WIBULL DISTRIBUTION……cont’d 69
WIBULL DISTRIBUTION……cont’d K=2 C=15 m/s EXCEL SHEET CALCULATIONS Description of excel program and varying the shape and scale factor in order to observe the occurrence of the speed probability.
WIBULL DISTRIBUTION……cont’d K=2 C=5 m/s EXCEL SHEET CALCULATIONS Description of excel program and varying the shape and scale factor in order to observe the occurrence of the speed probability.
WIBULL DISTRIBUTION……cont’d K=1 C=5 m/s EXCEL SHEET CALCULATIONS Description of excel program and varying the shape and scale factor in order to observe the occurrence of the speed probability.
WIBULL DISTRIBUTION……cont’d From Weibull distribution, the following conclusion can be drawn :
Application of Wiebull Distribution in Wind Energy…. . Now the question is How does the Weibull distribution related to assessing the metrics of wind energy ? This should be realized as follows
Application of Wiebull Distribution in Wind Energy…. . cont’d
Application of Wiebull Distribution in Wind Energy…. . cont’d Help, . . . SOS The best way to assimilate all this information is via example problem.
Example Problem#2 Find Vmode, Vmean, Vrms, the power density available distribution, and the power extracted per m 2 for a wind turbine at a site corresponding to a Weibull wind distribution with c=15 m/sec and k=1. 5. The air density is 1. 225 kg/m 3. Solution: The solution will be listed in five steps as follows: Step#1: Using Wiebul distribution/Excel sheet we found that the probable wind speed occurs at 7. 21 m/s as well shown on the figure. For Cpmax, the mode speed is around 7. 21 m/s
Example Problem#2 …. . cont’d Step#2: The power density for the mode speed is : Step#3: The mean wind speed is : Step#4: The power density for the mean speed is : Step#5: The root mean cube speed Vrmc is : Step#6: The power density for the cube speed is :
Example Problem#2…. . cont’d Step#7: The available power is : Step#8: The extracted annual energy is This means that each meter square of the turbine area (swept area) gives us an energy of 18110 k. W-hr/ year. Therefore, having a 10 m blade diameter of a wind turbine gives us a annually power of : 78. 539 m^2*18110 k. W-hr/year =1422356 k. W-hr/year =1. 422 MW-hr/ year Hurray, hurray, …. .
Example Problem#2 Now the described results can be obtained by using Math. CAD for solving the weibull equations and related to this equation power parameters. Also by using Excel Sheet for Weibul distribution we be able to determine the annual extracted power for a given k and c in particular for ( k=1. 5 & c=15 m/s)) ……cont’d
Example Problem#2 ……cont’d
Example Problem#2 ……cont’d The mode speed is 27 m/s where the maximum extracted power is <50% of the Annual.
Example Problem#3 Case study: Known that the wind speed in Palestine, approximately 8 m/s in winter/summer season, and we need an actual energy of 20 k. Whr. Determine 1 - the Turbine data 2 - the actual annual energy. Assume that the air density for warm climate is 1. 12 kg/m 3 Solution: According to the given data : c=8 m/s; =1. 12 kg/m 3; K=2; and Cp=45%, the following steps: Step#1: Using Wiebul distribution/Excel sheet we found that the probable wind speed occurs at 6 m/s as well shown on the figure.
Example Problem#3 ……cont’d The mode speed is 6 m/s where the total hours at this speed is 460 hours. 1502. 487 k. Wh/m 2 -year Step#2: Reading the data form the excel sheet/graph The mean speed is Vmean=7. 09 m /s ; Thr rmc speed Vrmc=8. 79 m/s The power density per m 2 is Pdensity (Vrmc)= 375. 58 k. W/m 2 The obtained annual energy per m 2 is Energy=1502. 48 k. Whr/m 2 -year
Example Problem#3 ……cont’d The mode speed is 11 m/s where the maximum extracted power is 45% of the Annual.
Example Problem#3 Step#3: Determine the blade dimensions… The swept /blade area is: The blade diameter is: The Solidity – Tower height = >3 x. R = 18. 5 m ……cont’d
WIND TURBINE OPERATION Wind turbine operation requires to answer the following question: What should the operating strategy be for the wind turbine as function of wind speed? The answer is not to operate the turbine at maximum wind power coefficient Cpmax. Why not to operate at Cpmax? . Operating at maximum Cp would maximize the extracted power; but factors such generator capacity (power and size), structural requirements (solid mechanical parts is required), and safety factor preclude (cause ineffective)) such operation.
WIND TURBINE OPERATION. . cont’d Knowing that maximum speed of the wind occurs for few number of hours a year. Which means, , we are designed an oversized generator, that in turn costs much money, and cannot found place in the market ( can't compete with other alternatives…). If the wind turbine is designed to operate at Cpmax , in order to keep the operation at maximum power extraction, the advanced ratio (TSR) must be increased in order to maintain Cp at constant value. Since the radial stresses in a rotor are proportional to the speed , therefore, keeping Cp at maximum values, means increasing the rotor speed, and in turn this requires a robust wind turbine which costs too much.
WIND TURBINE OPERATION. . cont’d But no matter what operating system is used, a wind turbine must contain a controller to implement the strategy, and mechanical elements to respond to this controller. The ultimate purpose of a wind turbine control strategy is to regulate the output power of the turbine as a function of wind speed and direction. Additionally the control protocol must ensure safe operation over all the wind conditions. The power outputs versus wind speed characteristic of a wind turbine can be viewed as being composed into several Operation modes /regions.
WIND TURBINE OPERATION. . cont’d
WIND TURBINE OPERATION. . cont’d The ordinate variables is the percentage of generator output, and the wind speed, where the operation conditions can be described as follows: First Regime/mode: the first condition(regime) is the cut-in speed of the system. Below the cut-in wind speed, the system components efficiencies are so low that running the system is not worth-while. During this condition the system operates in a constant Cp region. In this region, the turbine extracts the maximum power from the wind, but the power extracted is less than the rated input to the generator. The rotor speed is varied so that the advanced ratio is maintained near the maximum Cp value.
WIND TURBINE OPERATION. . cont’d Second Regime/mode: When the speed is sufficiently high, the extracted power by the rotor exceeds the rated input of the generator. In this regime, the system operates at constant output power mode, and the system is made to produce the rated output of the generator by operating the turbine at a Cp lower than Cpmax. The cut-out speed is the wind speed beyond which operation would damage the system. When the wind speed exceeds the cut-out speed, the braking system will operate to limit the motor speed(or totally locked), and also the pitch system will operate to unload the rotor. Help, . . . SOS The best way to assimilate all this information is via example problem.
WIND TURBINE OPERATION. . cont’d EXAMPLE PROBLEM #4 : The system described in in example #2, is specified to have cut-in speed at 5 m/s and to have cut-out speed at 35 m/s. . The rated generator input power is 7. 3 k. W/m 2, with Cp=0. 5 ( Cpnom=0. 5). Determine and plot the following for the system with and without controller to meet the constraints : • The power density of the system Cp versus wind speed required energy extraction, and total energy extracted by the system. Solution: Much of the information needed for the " no controls" part of this problem was developed in example#2. However, the solution procedure is:
WIND TURBINE OPERATION. . cont’d 1. The speed variable V should vary form 0 to 50 m/s ( v=0. . 50 m/s) 2. The average power density equals to : 3. The converted power density is a function of the Cp and speed limits :
WIND TURBINE OPERATION. . cont’d 4. The converted power density is a function of the Cp and speed limits : The obtained results for the power density and Cp are displayed graphically as follows: Figure (1), illustrates power densities as a function of the speed and constraints, Fig. 1: Power densities vs wind speed and constraints
WIND TURBINE OPERATION. . cont’d Fig. 2: Power coefficient vs wind speed Figure (2), illustratesthe power coefficient Cp as function of wind speed.
WIND TURBINE OPERATION. . cont’d 4. The energy densities for whole speed range per year equals to : Efficient operation This is the most revealing figure in wind turbine design, where the effect of cutin, cut-out speed and generator input power restrictions are quite evident in this figure. Inefficient operation
WIND TURBINE OPERATION. . cont’d 5. Finally, how much energy we can actually extract per year? : The energy densities integrated over all the speeds yield the total energy extracted. For the case of no-control strategy, the total energy extracted is 18110 k. Wh/yr/m 2, While the case corresponds to the implemented control constraints; the extract power is 11710 k. Wh/yr/m 2. Therefore the capture ratio is defined as the extracted power with control over the extracted power without control. . For our example the capture ratio is 65%. Which means that only 65% of the available energy can be extracted? . The next slide presents Math. CAD analysis of this example
WIND TURBINE OPERATION. . cont’d
WIND TURBINE OPERATION. . cont’d Now the question is Is it possible to increase the capture ratio? Yes, the only way to increase the capture ratio is by increasing the input power to the generator; or to increase the cut-out speed limit.
WIND TURBINE OPERATION. . cont’d DESPITE the high cost , good designed system must be characterized with ruggedness, reliability and stability, which means , at any fluctuation rate in wind speed ( within the constrains), direction, and generator speed, the produced power by the generator must be constant. Good design turbine is manufactured by Vestas Wind Systems with power of 800 k. W is shown on the figure.
WIND FARMS Sitting a Wind Farm THE FOLLOWING KEY FACTORS IN SITTING THE WND FARM
WIND FARMS…. . cont’d
WIND FARMS…. . cont’d
WIND FARMS…. . cont’d Wind Farm Arrangements THEY ARE ARRANGED IN ARRAYS: 2 -4 rotor diameters facing the prevailing wind Show me figure…. 8 -12 rotor diameter parallel to the wind speed.
WIND FARMS…. . cont’d For more than a single row of wind turbines in an array, the turbine locations in the succeeding row are staggered.
WIND ENERGY CHALLENGES… Market Barriers Wind Energy and the Grid Birds - A Serious Obstacle Wind – Characteristics & Consequences Balancing Supply & Demand
Market Barriers n Sitting n n n n Avian Noise Aesthetics / visualization Intermittent source of power Transmission constraints Operational characteristics different from conventional fuel sources Financing
Wind Energy and the Grid n Prospective n n Small project size Short/flexible development time Dispatchability Constrains n n n Generally remote location Grid connectivity -- lack of transmission capability Intermittent output n Only When the wind blows (night? Day? ) Low capacity factor (<40%) Predicting the wind
Wind – Characteristics & Consequences n Remote location (isolated locations) and low capacity factor n Small project size and quick development time n Higher transmission investment per unit output Planning mismatch with transmission investment Intermittent output Higher system operating costs if systems and protocols not designed properly.
Balancing Supply & Demand Peak consumption with WT contribution
WIND ECONOMICS n Wind economy triangle:
Wind Farm Design Economics n Key Design Parameters n n Mean wind speed at hub height Capacity factor n n n Start with 100% Subtract time when wind speed less than optimum (cut-in & cut-out) speeds. Subtract time due to scheduled maintenance Subtract time due to unscheduled maintenance Subtract production losses n n Dirty blades, shut down due to high winds, furies, harsh weather Typically 33% at a Class 4 wind site
Wind Farm Financing n Financing Terms n Interest rate n n LIBOR + basis points ( negotiated between the sponsor and the farm owner) Loan term n Up to 15 years
Cost of Energy Components n Cost (¢/k. Wh) = (Capital Recovery Cost + O&M) / k. Wh/year n n n Capital Recovery = Debt and Equity Cost O&M Cost = Turbine design, operating environment ( Operation & maintenance) k. Wh/year = Wind Resource
Construction Cost Elements
Wind Farm Cost Components
Wind Farm Cost Components
Improving the Capacity Factor n Performance Improvements can be realized by : n n n Better sitting Exploitation Larger turbines/ better energy capture Using Advanced control Technology Using high reliability systems Capacity factors > 35% at good sites
CASE STUDY- COST EXAMPLE A decision has been taken to invest and run in a wind farm with the following data: n 2 MW total power. n n Class 4 wind site n n n ( Site data reference) 33% capacity factor 2 Km to grid 6%/15 year financing n n Fixed costs - $1. 5 M/MW ( average cost) 100% financed 20 year project life Determine Cost of Energy - COE
CASE STUDY- COST EXAMPLE…. . cont’d n Total Capital Costs 2 MW*1. 5 M$/1 MW+ (2 km x $220 K/km) = $3. 44 M The cost of overhead transmission line is 220000$/1 k. M=220 k/1 k. M n n Total Annual Energy Production n n Total Energy Production ( over 20 yrs) n n 2. 95¢/k. Wh Operating Costs/k. Wh (~ 50% capital cost) n n 5, 781, 600 x 20 = 115, 632, 000 k. Wh Capital Costs/k. Wh n n 2 MW x 365 x 24 x 0. 33 = 5, 781, 600 k. Wh 1. 45¢/k. Wh Total cost of 1 k. Whr energy is : 4. 67¢/k. Wh 0. 18 NIS/k. Whr This is the net cost of the energy without trading/stock circulations…
Costs Nosedive Wind’s Success The cost of wind energy reduces by ~10 times during the past 30 years. 38 cents/k. Wh 3. 5 -5. 0 cents/k. Wh
Key parameters WIND FARM DEVELOPMENT Wind resource Zoning/Public Approval/Land Lease Power purchase agreements Connectivity to the grid Financing Tax incentives
WIND FARM DEVELOPMENT…cont’d n n Wind resource Absolutely vital to determine finances n n Requires historical wind data n n Daily and hourly detail Install metrological towers n n n Wind is the fuel Preferably at projected turbine hub height Multiple towers across proposed site Multiyear data reduces financial risk n Correlate long term offsite data to support short term onsite data.
WIND FARM DEVELOPMENT…cont’d n n Zoning/Public Approval/Land Lease Obtain local and Ministry/governmental approvals n Often includes Environmental Impact Studies n n Impact to wetlands, birds, noise, …. Negotiate lease/rental arrangements with land owners, farmers, municipalities, etc. n Annual payments per turbine or production based
WIND FARM DEVELOPMENT…cont’d Power Purchase Agreements (PPA) n n Must have upfront financial commitment from utility 15 to 20 year time frames Utility agrees to purchase wind energy at an reasonable set rate for e. g. (10 -12)¢/k. Wh (end consumer) Financial stability/credit rating of utility important aspect of obtaining wind farm financing n PPA only as good as the credit worthiness of the utility n Utility goes bankrupt – you’re in trouble
WIND FARM DEVELOPMENT…cont’d Connectivity to the grid n n Obtain approvals to tie to the grid n Obtain from grid operators/owners –PEA, HEBCO, SELCO. . Power fluctuations stress the grid n Especially since the grid is operating near max capacity
WIND FARM DEVELOPMENT…cont’d Financing n Once all components are settled… n n n n Wind resource Zoning/Public Approval/Land Lease Power Purchase Agreements (PPA) Connectivity to the grid Turbine procurement Construction costs …Take the deal to get financed……. .
DISCUSSION & CONCLUSION
Solar and Wind Energy Simulation Using Simulink The following webinars will be very helpful for you to evaluate the tools that Math. Works provide for sustainable energy simulation n Solar energy simulation: n http: //www. mathworks. com/company/events/webinars/wbnr 413 54. html? id=41354&p 1=697801410&p 2=697801422 n Wind energy simulation: n http: //www. mathworks. com/programs/wind_turbine_webinars/? BB=1 n To find more about the toolboxes that would be mentioned in those webinars, please refer to the following page for a comprehensive list: n http: //www. mathworks. com/products/product_listing/index. html
Workshop Internet Resources n n For this workshop, I plan to use the internet as a resourse. For example, to present solar energy, including the use of PV cells, I would refer you to www. photowatt. com and www. pvsquared. com. then, discuss the websites contents. for high brightness LEDs for building illuminations, visit www. diconlighting. com, and compare and contrast the system there with the other available systems, see www. powerpod. com. For Solar energy simulation visit the website: http: //www. mathworks. com/company/events/webina rs/wbnr 41354. html? id=41354&p 1=697801410&p 2=6 97801422 Alternative Energy Systems and Applications, B. K.
REFERENCES… n n n n Alternative Energy Systems and Applications, B. K. Hodge, John Wiley @ sons, 2010. Wind Turbine Power , Energy. , and Torque, Johnoson, G. L, 2001, Available at www. eece. ksu. edu/~gjohnson Wind Energy Fundamentals, resources, and Economics, Sathyajith Mathew, Springer-Verlag, 2006 World Resources Institute, www. wri. org Annual Energy Information report/ USA. http: //www. saferwholesale. com/product-p http: //www. alternative-energy-news. info
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