Let the Science Rule.

Transcription

1 COPE 11/02/2010 Wind Power Let the Science Rule Cork Hayden November 2, 2010 Coalition of Pueblo Engineers 1

2 Definition: Chromoergic psychosis The delusion that energy has a color, usually green November 2, 2010 Coalition of Pueblo Engineers 2

3 It s all about the air BASICS November 2, 2010 Coalition of Pueblo Engineers 3

4 Arrival Rate of KE at end of tube L A v November 2, KE 1 ALv 1 ALv Density, t 2 t 2 L/ v Mass M 1 3 Av 2 Coalition of Pueblo Engineers 4

5 Power Coefficient Power output The Power Coefficient is the efficiency of conversion of the wind s kinetic energy to mechanical energy Notice denominator in ordinate of attached graph C P saturates at 59% (Betz Limit) Best efficiency for few blades 1 2 Av vtip 3 November 2, 2010 Coalition of Pueblo Engineers vwind 5

6 Why use 3-bladed Turbines? Grab a textbook and wrap a rubber band around it to keep it closed Gently toss book kinto air rotating about each axis Pay attention to what happens! Top end Spine Cover November 2, 2010 Coalition of Pueblo Engineers 6

7 Results Axis 1: Cover remains up Axis 2: Top end remains at your left (or right) Axis 3: Spine switches sides, right-to-left to or left-to-right November 2, 2010 Coalition of Pueblo Engineers 7

8 Stability Maximum moment of finertia about taxis 1 Minimum moment of inertia about Axis 2 In-between moment of inertia i about Axis 3 Rotation is unstable 2-bladed d wind turbine is unstable Rotation axis has in-between moment of inertia 3-bladed wind turbine has equal moments about any two axes rotation axis, and highest moment about rotation axis November 2, 2010 Coalition of Pueblo Engineers 8

9 While we re at it A wind turbine is a gyroscope, with all its counterintuitive properties p When wind changes direction, there is a torque tending to tip up or tip down There has been some conjecture that the failure at Grandpa s Knob in Vermont in the 30s was caused by this effect. November 2, 2010 Coalition of Pueblo Engineers 9

10 The gyroscope effect Tips upward in front, downward in rear North East November 2, 2010 Coalition of Pueblo Engineers 10

11 Torque due to large force 80 m up at the nacelle Torque 5 million Nm ( 3.5 million ft-lb, 1,700 ton-feet). Foundation must be able to handle this torque November 2, 2010 Coalition of Pueblo Engineers 11

12 Power Coefficient C P Max Eff. Tip speed to 200 mph November 2, 2010 Coalition of Pueblo Engineers 12

13 SOME COMMERCIAL UNITS November 2, 2010 Coalition of Pueblo Engineers 13

14 GE 1.5-MW units 77 & 82.5-m diameter (250 & 270-ft) Hub Height: 65 & 80 m (213 & 262 ft) 1 Av 2.5*1.225 R v R 192 v 2 3 = 2.85 MW at 10 m/s November 2, 2010 Coalition of Pueblo Engineers 14

15 Vestas 1.8-MW unit has similar curve; C P = 35% also Power Curve (GE 1.5-MW) v < 4 m/s no power 4 < v < 11 m/s: v 3 region 11 < v < 13 m/s Transition 13 < v < 25 m/s Constant power Decreasing efficiency 1.0 MW/ 2.85 MW = 35% 77-m diam 82.5-m 20 & 25 m/s: Shut off November 2, 2010 Coalition of Pueblo Engineers 15

16 A Simple Engineering Result 1 1 P CP Av R v P R v (in SI units) Equation works from turn-on speed up to about 12 m/s November 2, 2010 Coalition of Pueblo Engineers 16

17 Small is Beautiful GE Sections of Vestas towers November 2, 2010 Coalition of Pueblo Engineers 17

18 CAPACITY FACTORS November 2, 2010 Coalition of Pueblo Engineers 18

19 Engineering the Capacity Factor C.F. = 0 CF.. P avg P nameplate Attach 1-MW generator to kid s pinwheel C.F. 100% Attach 1-watt bicycle generator to 30-m turbine Capacity factor is a matter of design! for a given site. Present standard: 35% November 2, 2010 Coalition of Pueblo Engineers 19

20 DISTRIBUTIONS November 2, 2010 Coalition of Pueblo Engineers 20

21 Hours vs velocity November 2, 2010 Coalition of Pueblo Engineers 21

22 Power vs Time (1) Wind speed may be highest when power is needed most ---or not Example: Power demand in Hawaii is highest just after sundown when the Kona winds die down And remember: P v 3 November 2, 2010 Coalition of Pueblo Engineers 22

23 Power vs Time (2) Jay Apt Jay Apt Pity the dispatcher who has to keep the grid stable November 2, 2010 Coalition of Pueblo Engineers 23

24 Over what time period? ENERGY STORAGE November 2, 2010 Coalition of Pueblo Engineers 24

25 Smoothing output Capacitor in inverter Rotational inertia 1,500 car batteries (better: deep-cycle) Compressed air in cavern Pumped-hydro Fraction of second Seconds to minutes 1 hour at 1.5-MW (at 100% conversion eff.) Problems: Running motors with variable power; power losses; resource availability November 2, 2010 Coalition of Pueblo Engineers 25

26 SPACING November 2, 2010 Coalition of Pueblo Engineers 26

27 Why not pack turbines close together? Turbine has extracted energy from the wind Allow some distance for wind speed to increase Turbulence! Why don t jet planes follow right behind one another? November 2, 2010 Coalition of Pueblo Engineers 27

28 Typical Spacing 10 diameters in both directions for wind coming from random directions 10 diameters along wind direction, 3 diameters across for prevailing winds Remember: P R 2 Double diameter 4 P Double diameter 4 land area Power per unit land area is indep. of diameter November 2, 2010 Coalition of Pueblo Engineers 28

29 Example P = 120*1.65 MW = 198 MW (nameplate) 21,000 acres P/A = 9,400 W/acre (nameplate) 3.3 kw/acre = 8.2 kw/ha = 0.8 W/m 2 (average) Btt Better places: 5kW/ kw/acre (12.5 kw/ha) average Most aren t this good November 2, 2010 Coalition of Pueblo Engineers 29

30 GENERATION ISSUES November 2, 2010 Coalition of Pueblo Engineers 30

31 Generation of Electricity South Poles Automotive alternator Voltage is proportional to RPM and dto rotor current Rotor current North Poles Voltage regulator adjusts rotor current to insure V out 13.5 V November 2, 2010 Coalition of Pueblo Engineers 31

32 Alternator Stator Each coil generates about 2 volts There are 6i in series S N 3 sets of coils generate 3-phase November 2, 2010 Coalition of Pueblo Engineers 32

33 Electricity from Giant Wind Turbines Electrical Generators usually turn at high (1,800) RPM Big wind turbines turn at low (10-15) RPM Gearboxes are used to increase RPM roughly 100-fold This is a real weakness! November 2, 2010 Coalition of Pueblo Engineers 33

34 Plan B: Use Permanent Magnets Increase diameter of generator Use many (N) permanent magnets on periphery of rotor Use 3 sets of N coils in series on stator Use direct drive: no gearbox November 2, 2010 Coalition of Pueblo Engineers 34

35 Problems with PM solution Permanent magnets require exotic, expensive materials SmCo 5, Nd 2 Fe 14 B, Sm 2 Fe 17 N x China is major supplier Output voltage RPM; not constant Output voltage can t be phase-locked to grid voltage Needs inverter November 2, 2010 Coalition of Pueblo Engineers 35

36 About rare earths Mark Smith, CEO, Molycorp Minerals (Smith): Actually we don't produce metals as of today. We mine the ore out of the ground, crush and mill the ore to create a concentrate, and then we go through a very sophisticated processing step to produce the rare earth oxides. There is only one country in the world today that can take the oxides and convert them to metals, and that's China. November 2, 2010 Coalition of Pueblo Engineers 36

37 Rare-Earth Magnets Let's take a look at wind turbines. In certain applications, two tons of rare earth magnets are required in the permanent magnet generator that goes on top of the turbine. If the permanent magnet is two tons, then 28% of that, or 560 lbs, is neodymium. (Correct value: 1120 lbs.) / i b/ i / i b/ / id t il November 2, 2010 Coalition of Pueblo Engineers 37

38 PERSPECTIVE November 2, 2010 Coalition of Pueblo Engineers 38

39 Electrical Production, % 36.5% 7% November 2, 2010 Coalition of Pueblo Engineers 39

40 Electrical Energy in TW e h (2008) Hydro Wind 52.0 Wood & Waste 22.3 Geothermal % Solar thermal/elec. & PV 0.8 TOTAL (all sources) November 2, 2010 Coalition of Pueblo Engineers 40

41 Making it personal 2008: US used 3.87 PW e h <P>=442P GW e For US population of 308 million, this is 1.43 kw e per capita For city of 700,000, this is 1 GW e. November 2, 2010 Coalition of Pueblo Engineers 41

42 Big City Typical city of 700,000 requires 1 GW e around-the-clock average power Average power from 300 mi 2 (750 km 2 ) of wind farm =1 GW e But sometimes there s no power and sometimes there s 3Xasmuchasneeded needed. Shut down turbines & kill C.F. November 2, 2010 Coalition of Pueblo Engineers 42

43 Environmentalists Wind turbines are not good neighbors Noise, infrasound, ground vibrations, shadowflicker, TV interference, radar interference, bird kills, bat kills, ice throws, BIG machinery moving very fast NIMBY is very often legitimate. Environmental groups opposed to wind abound November 2, 2010 Coalition of Pueblo Engineers 43

44 Vestas 1.8-MW unit (90-m diam) Far below lowest extent of blade Locomotive air horn at 100 feet in front: 98 db max (FRA rules) November 2, 2010 Coalition of Pueblo Engineers 44

45 Example The formula, which was developed by Robert Rand, an acoustic engineer, yields setbacks of 211 feet, for an extremely quiet turbine at 70 decibels, to setbacks of 37,584 feet, for a turbine operating at 115 decibels. Seven-mile setback! From p November 2, 2010 Coalition of Pueblo Engineers 45

46 785.1 MW (nameplate) 275 MW average on 100,000 acres 3872 MW on 4,050 acres Football field November 2, 2010 Coalition of Pueblo Engineers 46

47 MW per sq. mile Palo Verde Roscoe Wind Farm November 2, 2010 Coalition of Pueblo Engineers 47

48 Subsidies Renewables Nuclear Subsidies $/MWh Renewables Nuclear Ref from Droz: Energy-The-Truth-Blows h November 2, 2010 Coalition of Pueblo Engineers 48

49 Utilities Utilities would willingly buy low-cost electricity Why not? It would cut costs! But they have to be coerced to buy windgenerated electricity It s expensive and it s low-quality And you re helping to pay for it on April 15 th November 2, 2010 Coalition of Pueblo Engineers 49

50 Excellent source of energy information Energy Information Administration of the Department of Energy (presently) apolitical fact-finding group Look for Annual Energy Review by searching for aer2008 Caution: they use quadrillion BTU for thermal energy and billion kwh for electrical energy Hydro is rated at about 3 in BTU to specify the amount of thermal energy that would have to be used to replace it. November 2, 2010 Coalition of Pueblo Engineers 50

51 Q & A It s your turn November 2, 2010 Coalition of Pueblo Engineers 51

52 November 2, 2010 Coalition of Pueblo Engineers 52

53 Angular momentum in 3-D Position right hand so that fingers go in the direction (really, sense) of the rotation Extended thumb points in direction of angular momentum vector L Example: angular momentum L of bicycle wheel is toward the left of the rider. Hands of Clock: L into the wall November 2, 2010 Coalition of Pueblo Engineers 53

54 Torque in 3-D Change in angular momentum is parallel to torque November 2, 2010 Coalition of Pueblo Engineers 54

55 Change in Angular Momentum L L Horizontal for wind turbine L, parallel to torque (vertical for change of direction) November 2, 2010 Coalition of Pueblo Engineers 55