Wind Energy Basics

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• Wind Energy Basics

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Outline

• What is a wind plant?
• Power production
• Wind power equation
• Wind speed vs. height
• Usable speed range
• Problems with wind potential solutions

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1. What is a wind plant? Overview
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1. What is a wind plant? Tower Blades
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1. What is a wind plant? Towers, Rotors, Gens,
Blades
Manu-facturer Capacity Hub Height Rotor Diameter Gen type Weight (s-tons) Weight (s-tons) Weight (s-tons)
Manu-facturer Capacity Hub Height Rotor Diameter Gen type Nacelle Rotor Tower
0.5 MW 50 m 40 m
Vestas 0.85 MW 44 m, 49 m, 55 m, 65 m, 74 m 52m DFIG/Asynch 22 10 45/50/60/75/95, wrt to hub hgt
GE (1.5sle) 1.5 MW 61-100 m 70.5-77 m DFIG 50 31
Vestas 1.65 MW 70,80 m 82 m Asynch water cooled 57(52) 47 (43) 138 (105/125)
Vestas 1.8-2.0 MW 80m, 95,105m 90m DFIG/ Asynch 68 38 150/200/225
Enercon 2.0 MW 82 m Synchronous 66 43 232
Gamesa (G90) 2.0 MW 67-100m 89.6m DFIG 65 48.9 153-286
Suzlon 2.1 MW 79m 88 m Asynch
Siemens (82-VS) 2.3 MW 70, 80 m 101 m Asynch 82 54 82-282
Clipper 2.5 MW 80m 89-100m 4xPMSG 113 209
GE (2.5xl) 2.5 MW 75-100m 100 m PMSG 85 52.4 241
Vestas 3.0 MW 80, 105m 90m DFIG/Asynch 70 41 160/285
Acciona 3.0 MW 100-120m 100-116m DFIG 118 66 850/1150
GE (3.6sl) 3.6 MW Site specific 104 m DFIG 185 83
Siemens (107-vs) 3.6 MW 80-90m 107m Asynch 125 95 255
Gamesa 4.5 MW 128 m
REpower (Suzlon) 5.0 MW 100120 m Onshore90100 m Offshore 126 m DFIG/Asynch 290 120
Enercon 6.0 MW 135 m 126 m Electrical excited SG 329 176 2500
Clipper 7.5 MW 120m 150m
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1. What is a wind plant? Electric Generator
Type 1 Conventional Induction Generator (fixed
speed)
Type 2 Wound-rotor Induction Generator
w/variable rotor resistance
Type 3 Doubly-Fed Induction Generator (variable
speed)
Type 4 Full-converter interface
Plant
Feeders
ac
dc
generator
to
to
dc
ac
full power
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1. What is a wind plant? Type 3 Doubly Fed
Induction Generator

• Most common technology today
• Provides variable speed via rotor freq control
• Converter rating only 1/3 of full power rating
• Eliminates wind gust-induced power spikes
• More efficient over wide wind speed
• Provides voltage control

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1. What is a wind plant? Collector Circuit

• Distribution system, often 34.5

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1. What is a wind plant? Offshore

• About 600 GW available 5-50 mile range
• About 50 GW available in lt30m water
• Installed cost 3000/MW uncertain because US
  cont. shelf deeper than N. Sea

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2. Power production Wind power equation

• The disks have larger cross sectional area from
  left to right because
• v1 gt vt gt v2 and
• the mass flow rate must be the same everywhere
  within the streamtube.
• Therefore, A 1 lt At lt A 2

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2. Power production Wind power equation
3. Mass flow rate at swept area
4b. Force on turbine blades
4a. Kinetic energy change
5b. Power extracted
5a. Power extracted
6b. Substitute (3) into (5b)
6a. Substitute (3) into (5a)
7. Equate
8. Substitute (7) into (6b)
9. Factor out v13
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2. Power production Wind power equation
10. Define wind stream speed ratio, a
This ratio is fixed for a given turbine control
condition.
11. Substitute a into power expression of (9)
12. Differentiate and find a which maximizes
function
13. Find the maximum power by substituting a1/3
into (11)
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2. Power production Wind power equation
14. Define Cp, the power (or performance)
coefficient, which gives the ratio of the power
extracted by the converter, P, to the power of
the air stream, Pin.
power extracted by the converter
power of the air stream
15. The maximum value of Cp occurs when its
numerator is maximum, i.e., when a1/3
The Betz Limit!
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2. Power production Cp vs. a
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2. Power production Cp vs. ? and ?
u tangential velocity of blade tip
Tip-speed ratio
? rotational velocity of blade
R rotor radius
v1 wind speed
Pitch ?
GE SLE 1.5 MW
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2. Power production Cp vs. ? and ?
u tangential velocity of blade tip
Tip-speed ratio
? rotational velocity of blade
R rotor radius
v1 wind speed
Pitch ?
GE SLE 1.5 MW
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2. Power production Wind Power Equation

• So power extracted depends on
• Design factors
• Swept area, At
• Environmental factors
• Air density, ? (1.225kg/m3 at sea level)
• Wind speed v3
• 2. Control factors
• Tip speed ratio through the rotor speed ?
• Pitch ?

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2. Power production Control
In Fig. a, a dotted curve is drawn through the
points of maximum torque. This curve is very
useful for control, in that we can be sure that
as long as we are operating at a point on this
curve, we are guaranteed to be operating the wind
turbine at maximum efficiency. Therefore this
curve, redrawn in Fig. b, dictates how the
machine should be controlled in terms of torque
and speed.
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2. Power production Effects on wind speed
Location
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2. Power production Effects on wind speed
Location
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2. Power production Effects on wind speed Height
In the daytime, when 10 m temperature is greater
than at 80 m, the difference between the wind
speeds is small due to solar irradiation, which
heats the ground and causes buoyancy such that
turbulent mixing leads to an effective coupling
between the wind fields in the surface layer.
During nighttime the temperature DIFFERENCE
changes sign because of the cooling of the
ground. This inversion dampens turbulent mixing
and, hence, decouples the wind speed at different
heights, leading to pronounced differences
between wind speeds.
T80m lt T10m ?Ground heating?Air rise ?Turbulent
mixing?Coupling ? v80m v10m
Source M. Lange and U. Focken, Physical
approach to Short-Term Wind Power Prediction,
Springer, 2005.
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2. Power production Effects on wind speed Height
The mean values of the wind speed show a
pronounced dirunal cycle. At 10 m, the mean wind
speed has a maximum at noon and a minimum around
midnight. This behavior changes with increasing
height, so that at 200 m, the dirunal cycle is
inverse, with a broad minimum in daytime and
maximum wind speeds at night. Hence, the better
the coupling between the atmospheric layers
during the day, the more horizontal momentum is
transferred downwards from flow layers at large
heights to those near the ground.
Average wind speed increases with height.
Source M. Lange and U. Focken, Physical
approach to Short-Term Wind Power Prediction,
Springer, 2005.
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2. Power production Effects on wind speed Height
The atmosphere is divided into several
horizontal layers to separate different flow
regimes. These layers are defined by the
dominating physical effects that influence the
dynamics. For wind energy use, the troposphere
which spans the first five to ten km above the
ground has to be considered as it contains the
relevant wind field regimes.
Source M. Lange and U. Focken, Physical
approach to Short-Term Wind Power Prediction,
Springer, 2005.
?Wind shear exponent differs locationally U wind
speed estimate at Hub Height Href is height at
which reference data was taken Uref is wind
speed at height of Href
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2. Power production Effects on wind speed
Contours
Wind profile at top of slope is fuller than
that of approaching wind.
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2. Power production Effects on wind speed
Roughness
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2. Power production Usable speed range
Cut-in speed (6.7 mph)
Cut-out speed (55 mph)
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3. Problems with wind potential
solutions Day-ahead forecast uncertainty

• Fossil-generation is planned day-ahead
• Fossil costs minimized if real time same as plan
• Wind increases day-ahead forecast uncertainty

• Solutions
• Pay increased fossil costs from fossil energy
  displaced by wind
• Use fast ramping gen
• Distribute wind gen widely
• Improve forecasting
• Smooth wind plant output
• On-site regulation gen
• Storage

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3. Problems with wind potential solutions Daily,
annual wind peak not in phase w/load

• Daily wind peaks may not coincide w/ load
• Annual wind peaks occur in winter

• Solutions
• Spill wind
• Shift loads in time
• Storage
• Pumped storage
• Pluggable hybrid vehicles
• Batteries
• H2, NH3 with fuel cell
• Compressed air
• others

Midwestern Region
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3. Problems with wind potential solutions Wind
Power Movies
JULY2006 JANUARY2006
Notice January has a lot more high-wind power
than July. Also notice how the waves of wind
power move through the entire EI.
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3. Problems with wind potential solutions Cost
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3. Problems with wind potential solutions Cost
1050/kW capital cost 34 capacity factor
50-50 capital structure 7 debt cost 12.2
eqty rtrn 20-year depreciation life 25,000
annual O M per MW ?20-year levlzd cost5/kWhr
Existing coal lt2.5/kWhr Existing Nuclear
lt3.0/kWhr New gas combined cycle
gt6.0/kWhr New gas combustion turbine
gt10/kWhr

• Solution
• Cost of wind reduces with tower height
• Tower designs, nacelle weight reduction,
  innovative constructn
• Carbon cost makes wind good (best?) option

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3. Problems with wind potential solutions Wind
is remote from load centers
Transmission cost a small fraction of total
investment operating costs.

• And it can pay for itself
• Assume 80B provides 20,000 MW delivery system
  over 30 years, 70 capacity factor, for Midwest
  wind energy to east coast.
• This adds 21/MWh.
• Cost of Midwest energy is 65/MWh.
• Delivered cost of energy would then be 86/MWh.
• East coast cost is 110/MWh.

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Conclusions

• High penetration levels require solution to
  cost, variability, and transmission.
• Wind economics driven by wind speed, thus by
  turbine height.
• Solutions to variability and transmission
  problems could increase growth well beyond what
  is not being predicted.

Source European Wind Energy Association, Wind
Energy The Facts, Earthscan, 2009.