Wind Energy Basics

rangebeaverΜηχανική

22 Φεβ 2014 (πριν από 3 χρόνια και 7 μήνες)

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Wind Energy Basics

Outline

1.
What

is

a

wind

plant?

2.
Power

production

a.
Wind

power

equation

b.
Wind

speed

vs
.

height

c.
Usable

speed

range

3.
Problems

with

wind
;

potential

solutions

1. What is a wind plant?

Overview

1. What is a wind plant? Tower & Blades

4

1. What is a wind plant? Towers, Rotors, Gens, Blades

5

Manu
-
facturer

Capacity

Hub Height

Rotor
Diameter

Gen type

Weight (s
-
tons)

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

100

120 m Onshore

90

100 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

1. What is a wind plant?

Electric Generator

6

generator

full power

Plant

Feeders

ac

to

dc

dc

to

ac

generator
partial power
Plant
Feeders
ac
to
dc
dc
to
ac
generator
Slip power
as heat loss
Plant
Feeders
PF control
capacitor s
ac
to
dc
generator
Plant
Feeders
PF control
capacitor s
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

1. What is a wind plant?

Type 3 Doubly Fed Induction Generator

7

generator
partial power
Plant
Feeders
ac
to
dc
dc
to
ac


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

1. What is a wind plant?

Collector Circuit



Distribution system, often 34.5

8

POI or
connection
to the grid
Collector System
Station
Feeders and Laterals (overhead
and/or underground)
Individual WTGs
Interconnection
Transmission Line

1. What is a wind plant?

Offshore



About 600 GW available 5
-
50 mile range



About 50 GW available in <30m water



Installed cost ~$3000/MW; uncertain

because
US cont. shelf deeper than N. Sea

9

2. Power production

Wind power equation

v
1

v
t

v
2

v

x


Swept area A
t

of turbine blades:

The disks have larger cross
sectional area from left to
right because



v
1

> v
t

> v
2

and



the mass flow rate must
be the same everywhere
within the streamtube.


Therefore, A

1

< A
t

< A

2


2. Power production

Wind power equation

t
t
t
t
v
A
t
x
A
t
m
Q









3. Mass flow rate at swept area:



2
2
2
1
2
1
v
v
m
KE



1. Wind velocity:

t
x
v



x
A
m




2. Air mass flowing:

4a. Kinetic energy change:

5a. Power extracted:





2
2
2
1
2
2
2
1
2
1
2
1
v
v
Q
v
v
t
m
t
KE
P
t








6a. Substitute (3) into (5a):

)
(
)
2
/
1
(
2
2
2
1
v
v
v
A
P
t
t



4b. Force on turbine blades:



2
1
v
v
Q
v
t
m
t
v
m
ma
F
t









5b. Power extracted:



2
1
v
v
v
Q
Fv
P
t
t
t



6b. Substitute (3) into (5b):

)
(
2
1
2
v
v
v
A
P
t
t



t
t
t
t
t
v
v
v
v
v
v
v
v
v
v
v
v
v
v
v
v
v












)
)(
2
/
1
(
)
(
)
)(
(
)
2
/
1
(
)
(
)
(
)
2
/
1
(
1
2
2
1
2
2
1
2
1
1
2
2
2
1
2
2
7. Equate

8. Substitute (7) into (6b):

)
)(
(
4
)
(
))
)(
2
/
1
((
2
1
2
2
2
1
2
1
2
2
1
v
v
v
v
A
v
v
v
v
A
P
t
t








9. Factor out v
1
3
:

)
1
)(
)
(
1
(
4
1
2
2
1
2
3
1
v
v
v
v
v
A
P
t




2. Power production

Wind power equation

10. Define wind
stream speed ratio,
a
:

1
2
v
v
a

)
1
)(
1
(
4
2
3
1
a
a
v
A
P
t




11. Substitute
a

into
power expression of (9):

12. Differentiate and find
a

which maximizes function:



1
,
3
/
1
0
)
1
)(
1
3
(
0
1
2
3
1
2
2
0
)
1
(
)
1
(
2
4
2
2
2
2
3
1

























a
a
a
a
a
a
a
a
a
a
a
a
v
A
a
P
t

This ratio is fixed for a given
turbine & control condition.

13. Find the maximum power
by substituting
a=1/3

into (11):

27
8
3
4
9
8
4
)
3
4
)(
9
1
1
(
4
3
1
3
1
3
1
v
A
v
A
v
A
P
t
t
t







2. Power production

Wind power equation

14. Define C
p
, the power (or performance) coefficient, which
gives the ratio of the power extracted by the converter, P, to
the power of the air stream, P
in
.

)
1
)(
1
(
4
2
3
1
a
a
v
A
P
t






3
1
2
1
1
2
1
1
2
1
2
1
2
1
2
1
0
2
1
v
A
v
v
A
v
Q
v
t
m
t
KE
P
t
t
in











power extracted

by the converter

power of the

air stream

)
1
)(
1
(
2
1
2
1
)
1
)(
1
(
4
2
3
1
2
3
1
a
a
v
A
a
a
v
A
P
P
C
t
t
in
p









15. The maximum value of C
p

occurs when its numerator
is maximum, i.e., when a=1/3:

5926
.
0
27
16
)
3
4
)(
9
8
(
2
1




in
p
P
P
C
The Betz Limit!

3
1
2
1
v
A
C
P
C
P
t
P
in
p



2. Power production

Cp vs. a

2. Power production

Cp vs.
λ

and
θ

Tip
-
speed

ratio
:

1
1
v
R
v
u




u: tangential velocity of blade tip

ω: rotational velocity of blade

R: rotor radius

v
1
: wind speed

Pitch
:

θ


GE SLE 1.5 MW

2. Power production

Cp vs.
λ

and
θ

Tip
-
speed

ratio
:

1
1
v
R
v
u




u: tangential velocity of blade tip

ω: rotational velocity of blade

R: rotor radius

v
1
: wind speed

Pitch
:

θ


GE SLE 1.5 MW

2. Power production

Wind Power Equation

3
1
)
,
(
2
1
v
A
C
P
C
P
t
P
in
p





So power extracted depends on

1.
Design factors:



Swept area, A
t


2.
Environmental factors:



Air density,
ρ

(~1.225kg/m
3

at sea level)



Wind speed v
3

2. Control factors:



Tip speed ratio through the rotor speed
ω



Pitch
θ

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.

2. Power production

Effects on wind speed: Location

Wind
Wind
Speed
(b)
Wind
Speed
(b)
Power
Power
m/s (mph)
Power
m/s (mph)
Class
Density
Density
(W/m
2
)
(W/m
2
)
1
<100
<4.4 (9.8)
<200
<5.6 (12.5)
2
100 - 150
4.4
(9.8)/5.1
200 - 300
5.6
(12.5)/6.4
3
150 - 200
5.1
(11.5)/5.6
300 - 400
6.4
(14.3)/7.0
4
200 - 250
5.6
(12.5)/6.0
400 - 500
7.0
(15.7)/7.5
5
250 - 300
6.0
(13.4)/6.4
500 - 600
7.5
(16.8)/8.0
6
300 - 400
6.4
(14.3)/7.0
600 - 800
8.0
(17.9)/8.8
7
>400
>7.0 (15.7)
>800
>8.8 (19.7)
Classes of Wind Power Density at 10 m and
50 m
(a)

10 m (33 ft)

50 m (164 ft)
2. Power production

Effects on wind speed: Location

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.”

Source: M. Lange and U. Focken, “Physical approach to Short
-
Term Wind Power Prediction,”
Springer, 2005.

T
80m

< T
10m


Ground heating

Air rise


Turbulent mixing

Coupling



v
80m

~ v
10m

2. Power production

Effects on wind speed: Height

Source: M. Lange and U. Focken, “Physical approach

to Short
-
Term Wind Power Prediction,” Springer, 2005.

“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.”

Daytime peak occurs at 10 m.

Nighttime peak occurs at 200 m.

Almost flat at 80 m.

Average wind speed
increases with height.

2. Power production

Effects on wind speed: Height

7
1
Height

Hub









ref
ref
H
U
U

Wind shear exponent differs locationally

U: wind speed estimate at Hub Height

H
ref

is height at which reference data was taken

U
ref

is wind speed at height of H
ref

“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.

2. Power production

Effects on wind speed: Contours

Wind profile at top of
slope is fuller than that

of approaching wind.

2. Power production

Effects on wind speed: Roughness

2. Power production

Usable speed range

Cut
-
in speed (6.7 mph)

Cut
-
out speed (55 mph)

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

27

Hourly Load Variability and Load-Wind Variability When Wind
Penetration is 10%
0
500
1000
1500
2000
2500
3000
3500
4000
-800
-700
-600
-500
-400
-300
-200
-100
0
100
200
300
400
500
600
700
800
Load and Load-Wind Hourly Variability (MW)
Freqency
Load Hourly Variability
Load-Wind Hourly Variability
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

3. Problems with wind; potential solutions

Daily, annual wind peak not in phase w/load

28

Solutions
:



“Spill” wind



Shift loads in time



Storage



Pumped storage



Pluggable hybrid vehicles



Batteries



H
2
, NH
3

with fuel cell



Compressed air



…others



Daily wind peaks may not coincide w/ load



Annual wind peaks occur in winter

Midwestern Region

3. Problems with wind; potential solutions

Wind Power Movies

29

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.

3. Problems with wind; potential solutions

Cost

30

31

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 cost=5¢/kWhr

• Existing coal: <2.5¢/kWhr

• Existing Nuclear: <3.0¢/kWhr

• New gas combined cycle:


>6.0¢/kWhr

• New gas combustion turbine:


>10¢/kWhr

Solution
:



Cost of wind reduces with tower height



Tower designs, nacelle weight reduction, innovative constructn



Carbon cost makes wind good (best?) option

3. Problems with wind; potential solutions
Wind is remote from load centers

32

20% Wind Future Cumulative
Costs through 2024
68%
30%
2%
Production
Generation Capital
Transmission Capital
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.

Conclusions

Source: European Wind Energy Association,

“Wind Energy


The Facts,” Earthscan, 2009.



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.