Wind Energy

1
ECE 333 Green Electric Energy

• Lecture 20
• Wind Energy
• Professor Tom Overbye
• Department of Electrical andComputer Engineering

2
Announcements

• Start reading Chapter 6.
• Homework 8 is due now.
• Homework 9 is 6.12, 6.14, 6.15. It doesnt need
  to be turned in but should be completed before
  the test. Kate will post solutions by next
  Tuesday.
• Exam 2 is Thursday November 19 in class. You can
  bring in your old note sheet and one new notes
  sheet. Kate is posting exam 2 from last
  semester.

3
Ex. 6.11 Annual Energy from a Wind Turbine

• NEG Micon 750/48 (750 kW and 48 m rotor)
• Tower is 50 m
• In the same area, vavg is 5m/s at 10 m
• Assume standard air density, Rayleigh statistics,
  Class 1 surface, (total) efficiency is 30
• Find the annual energy (kWh/yr) delivered

4
Ex. 6.11 Annual Energy from a Wind Turbine

• We need to use (6.16) to find v at 50 m, where z
  for roughness Class 1 is 0.03 m (from Table 6.4)
• Then, the average power density in the wind at 50
  m from (6.48) is

5
Ex. 6.11 Annual Energy from a Wind Turbine

• The rotor diameter is 48 m and the total
  efficiency is 30, so the average power from the
  wind turbine is
• Then, the energy delivered in a year is

6
Wind Farms

• Normally, it makes sense to install a large
  number of wind turbines in a wind farm or a wind
  park
• Benefits
• Able to get the most use out of a good wind site
• Reduced development costs
• Simplified connections to the transmission system
• Centralized access for operations and maintenance
• How many turbines should be installed at a site?

7
Wind Farms

• We know that wind slows down as it passes through
  the blades. Recall the power extracted by the
  blades
• Extracting power with the blades reduces the
  available power to downwind machines
• What is a sufficient distance between wind
  turbines so that windspeed has recovered enough
  before it reaches the next turbine?

8
Wind Farms
For closely spaced towers, efficiency of the
entire array becomes worse as more wind turbines
are added
Figure 6.28
9
Wind Farms

• The study in Figure 6.28 considered square
  arrays, but square arrays dont make much sense
• Rectangular arrays with only a few long rows are
  better
• Recommended spacing is 3-5 rotor diameters
  between towers in a row and 5-9 diameters between
  rows
• Offsetting or staggering the rows is common
• Direction of prevailing wind is common

10
Wind Farms Optimum Spacing
Ballparkfigure for GE 1.5 MW in Midwestis one
per80 acres
3 D to 5D
Figure 6.29
Optimum spacing is estimated to be 3-5 rotor
diameters between towers and 5-9 between rows
5 D to 9D
11
Ex. 6.12 Energy Potential for a Wind Farm

• A wind farm has 4-rotor diameter spacing along
  its rows, 7-rotor diameter spacing between the
  rows
• WTG efficiency is 30, Array efficiency is 80

4D
7D
Note that the 4D and the 7D are switched on the
figure in the book.
12
Ex. 6.12 Energy Potential for a Windfarm
4D
7D

• a. Find annual energy production per unit of
  land area if the power density at hub height is
  400-W/m2 (assume 50 m, Class 4 winds)
• b. What does the lease cost in /kWh if the land
  is leased from a rancher at 100 per acre per
  year?

13
Ex. 6.12 Energy Potential for a Windfarm

• a. For 1 wind turbine

14
Ex. 6.12 Energy Potential for a Windfarm

• b. 1 acre 4047m2

In part (a), we found
or equivalently
Then, the lease cost per kWh is
15
Time Variation of Wind

• We need to not just consider how often the wind
  blows but also when it blows with respect to the
  electric load.
• Wind patterns vary quite a bit with geography,
  with coastal and mountain regions having more
  steady winds.
• In the Midwest the wind tends to blow the
  strongest when the electric load is the lowest.

16
Upper Midwest Daily Wind Variation
August
April
Source www.uwig.org/XcelMNDOCwindcharacterization
.pdf
17
How Rotor Blades Extract Energy from the Wind
Airfoil could be the wing of an airplane or the
blade of a wind turbine

• Bernoullis Principle - air pressure on top
  is lower than air pressure on bottom because it
  has further to travel, creates lift

Figure 6.30 (a)
18
How Rotor Blades Extract Energy from the Wind

• Air is moving towards the wind turbine blade from
  the wind but also from the relative blade motion
• The blade is much faster at the tip than at the
  hub, so the blade is twisted to keep the angles
  correct

Figure 6.30 (b)
19
Angle of Attack, Lift, and Drag

• Increasing angle of attack increases lift, but it
  also increases drag

Figure 6.31 (a)

• If the angle of attack is too great, stall
  occurs where turbulence destroys the lift

Figure 6.31 (b) - Stall
20
Idealized Power Curve

• Cut in windspeed, rated windspeed, cut-out
  windspeed

Figure 6.32
21
Idealized Power Curve

• Before the cut-in windspeed, no net power is
  generated
• Then, power rises like the cube of windspeed
• After the rated windspeed is reached, the wind
  turbine operates at rated power (sheds excess
  wind)
• Three common approaches to shed excess wind
• Pitch control physically adjust blade pitch to
  reduce angle of attack
• Stall control (passive) blades are designed to
  automatically reduce efficiency in high winds
• Active stall control physically adjust blade
  pitch to create stall

22
Idealized Power Curve

• Above cut-out or furling windspeed, the wind is
  too strong to operate the turbine safely, machine
  is shut down, output power is zero
• Furling refers to folding up the sails when
  winds are too strong in sailing
• Rotor can be stopped by rotating the blades to
  purposely create a stall
• Once the rotor is stopped, a mechanical brake
  locks the rotor shaft in place

23
Example Small Wind Turbine

• Consider a 0.9 kW wind turbine with a 2.13m blade
  installed at a hub height where the average wind
  speed is 6.7 m/s.
• Assume the turbine costs 1,600 and the
  installation/other capital costs add an
  additional 900
• The 2,500 total capital is financed with a
  15-year, 7 load.
• Annual OM costs are 100
• The capital recovery factor (i0.07, n 15) is
  0.1087
• Total annual payments are thus (25000.1087100)
  374.49/yr

24
Example Small Wind Turbine, cont.

• To estimate the energy delivered by the turbine
  well use the CF approach from (6.65)
• Total energy supplied by turbine would be
  about(0.9)kW?(8760)hr/yr ?0.385 3035 kWh/yr
• Average cost per kWh is then 374.5/3035 0.123
  /kWh
• This value is close to current rates, and also
  assumes the wind turbine only lasts for 15 years.
• Note, a 6.7 m/sec average wind is class 3 (much
  of Illinois at 50m)

25
Current Prices for Small Wind

• The Home Depot is selling a 900W wind turbine
  kit, which includes the turbine and a 1000W
  inverter, for 2497.97 tower and batteries are
  extra (65 tower goes for about 1000 plus
  installation).

MostIllinoissites are lt 12 mphat 65
Source www.homedepot.com www.kansaswindpower.net
26
Government Credits

• Federal government provides tax credits of 30 of
  cost for small (household level) solar, wind,
  geothermal and fuel cells (starting in 2009 the
  total cap of 4000 was removed)
• I dont think Illinois has a wind credit, but
  they do have a solar credit (30 of cost)
• For large systems the Federal Renewable
  Electricity Production Tax Credit pays 1.5/kWh
  (1993 dollars, inflation adjusted, currently
  2.1) for the first ten years of production

Source for federal/state incentives
www.dsireusa.org
27
Economies of Scale

• Presently large wind farms produce electricity
  more economically than small operations
• Factors that contribute to lower costs are
• Wind power is proportional to the area covered by
  the blade (square of diameter) while tower costs
  vary with a value less than the square of the
  diameter
• Larger blades are higher, permitting access to
  faster winds
• Fixed costs associated with construction
  (permitting, management) are spread over more MWs
  of capacity
• Efficiencies in managing larger wind farms
  typically result in lower OM costs (on-site
  staff reduces travel costs)

28
Environmental Aspects of Wind Energy

• US National Academies issued report on issue in
  2007
• Wind system emit no air pollution and no carbon
  dioxide they also have essentially no water
  requirements
• Wind energy serves to displace the production of
  energy from other sources (usually fossil fuels)
  resulting in a net decrease in pollution
• Other impacts of wind energy are on animals,
  primarily birds and bats, and on humans

29
Environmental Aspects of Wind Energy, Birds and
Bats

• Wind turbines certainly kill birds and bats, but
  so do lots of other things windows kill between
  100 and 900 million birds per year

Estimated Causes of Bird Fatalities, per 10,000
Source Erickson, et.al, 2002. Summary of
Anthropogenic Causes of Bird Mortality
30
Environmental Aspects of Wind Energy, Birds and
Bats

• Of course most people do not equate killing a
  little song bird, like a sparrow, the same as
  killing a bigger bird, like an eagle (less prone
  to hit the front window).
• Large bird (raptor) mortalities are about 0.04
  bird/MW/year, but these values vary substantially
  by location with Altamont Pass (CA) killing about
  1 raptor/MW/year.
• Turbine design and location has a large impact on
  mortality

31
Environmental Aspects of Wind Energy, Human
Aesthetics

• Aesthetics is often the primary human concern
  about wind energy projects (beauty is in the eye
  of the beholder) night lighting can also be an
  issue

Figure 4-1 of NAS Report, Mountaineer Project 0.5
miles
32
Environmental Aspects of Wind Energy, Human
Aesthetics, Offshore

• Offshore wind turbines currently need to be in
  relatively shallow water, so maximum distance
  from shore depends on the seabed
• Capacityfactors tendto increaseas
  turbinesmove furtheroff-shore

Image Source National Renewable Energy Laboratory
33
Cape Wind Simulated View, Nantucket Sound, 6.5
miles Distant
Source www.capewind.org
34
Environmental Aspects of Wind Energy, Human
Well-Being

• Wind turbines often enhance the well-being of
  many people, but some living nearby may be
  affected by noise and shadow flicker
• Noise comes from 1) the gearbox/generator and 2)
  the aerodynamic interaction of the blades with
  the wind
• Noise impact is usually moderate (50-60 dB) close
  (40m), and lower further away (35-45 dB) at 300m
• However wind turbine frequencies also need to be
  considered, with both a hum frequency above 100
  Hz, and some inaudible or barely audible low
  frequencies (20 Hz or less)
• Shadow flicker is more of an issue in high
  latitude countries since a lower sun casts longer
  shadows

35
Questions Landowners Should Consider Before
Signing Up

• How much do I get and how much land will be tied
  up and for how long (usually about 3000/yr per
  turbine)
• Is it fixed or based on revenue?
• What land rights are given up what can I still
  do?
• Who has what liability insurance?
• What rights is the developer able to transfer
  without my consent?
• What are my and the developers termination
  rights?
• If the agreement is terminated, what happens to
  the wind energy structures and related facilities
  (they take a lot of concrete!)

36
Wind Turbines and Property Taxes in Illinois

• Illinois taxes property (land/buildings) at a
  rate equal to 1/3 its fair cash value.
• Personal property is not taxed (e.g., they tax
  your house but not what you have in your house).
• Beginning in 2008 Illinois assigns a fair cash
  value to wind turbines based at a rate of
  360,000 per MWan inflation value (set to 1.0 in
  2008) a depreciation value.
• Property tax rates in Champaign county are around
  7 to 8 /100. At 8 the owner of 1.5 MW wind
  turbine would need to pay 9600 per year, which
  is about 2.4 per MWh (assuming a 30 capacity
  factor)

37
Power Grid Integration of Wind Power

• Currently wind power represents a minority of the
  generation in power system interconnects, so its
  impact of grid operations is small
• But as wind power grows, in the not too distant
  future it will have a much larger, and perhaps
  dominant impact of grid operations
• Wind power has impacts on power system operations
  ranging from that of transient stability
  (seconds) out to steady-state (power flow)
• Voltage and frequency impacts are key concerns

38
Wind Power, Reserves and Regulation

• A key constraint associated with power system
  operations is pretty much instantaneously the
  total power system generation must match the
  total load plus losses
• Excessive generation increases the system
  frequency, while excessive load decreases the
  system frequency
• Generation shortfalls can suddenly occur because
  of the loss of a generator utilities plan for
  this occurrence by maintaining sufficient
  reserves (generation that is on-line but not
  fully used) to account for the loss of the
  largest single generator in a region (e.g., a
  state)

39
Wind Power, Reserves and Regulation, cont.
Eastern Interconnect Frequency Response for Loss
of 2600 MW
40
Wind Power, Reserves and Regulation, cont.

• A fundamental issue associated with free fuel
  systems like wind is that operating with a
  reserve margin requires leaving free energy on
  the table.
• A similar issue has existed with nuclear energy,
  with the fossil fueled units usually providing
  the reserve margin
• Because wind turbine output can vary with the
  cube of the wind speed, under certain conditions
  a modest drop in the wind speed over a region
  could result in a major loss of generation
• Lack of other fossil-fuel reserves could
  exacerbate the situation

41
Wind Power and the Power Flow

• The most common power system analysis tool is the
  power flow (also known sometimes as the load
  flow)
• power flow determines how the power flows in a
  network
• also used to determine all bus voltages and all
  currents
• because of constant power models, power flow is a
  nonlinear analysis technique
• power flow is a steady-state analysis tool
• it can be used as a tool for planning the
  location of new generation, including wind

42
Five Bus Power Flow Example
43
37 Bus Power Flow Example
44
Good Power System Operation

• Good power system operation requires that there
  be no reliability violations for either the
  current condition or in the event of
  statistically likely contingencies
• Reliability requires as a minimum that there be
  no transmission line/transformer limit violations
  and that bus voltages be within acceptable limits
  (perhaps 0.95 to 1.08)
• Example contingencies are the loss of any single
  device. This is known as n-1 reliability.
• North American Electric Reliability Corporation
  now has legal authority to enforce reliability
  standards (and there are now lots of them). See
  http//www.nerc.com for details (click on
  Standards)

45
Looking at the Impact of Line Outages
Opening one line (Tim69-Hannah69) causes an
overload. This would not be allowed (i.e., we
cant operate this way when line is in.
46
Contingency Analysis
Contingencyanalysis providesan automaticway of
lookingat all the statisticallylikely
contingencies. Inthis example thecontingency
set Is all the single line/transformeroutages
47
Generation Changes and The Slack Bus

• The power flow is a steady-state analysis tool,
  so the assumption is total load plus losses is
  always equal to total generation
• Generation mismatch is made up at the slack bus
• When doing generation change power flow studies
  one always needs to be cognizant of where the
  generation is being made up
• Common options include system slack, distributed
  across multiple generators by participation
  factors or by economics

48
Generation Change Example 1
Display shows Difference Flows between original
37 bus case, and case with a BLT138 generation
outage note all the power change is picked up
at the slack
49
Generation Change Example 2
Display repeats previous case except now the
change in generation is picked up by other
generators using a participation factor approach
50
Siting New Wind Generation Example