Assessing the Impact of Distributed Wind Generation

Assessing the Impact ofDistributed Wind Generation

Tom McDermott, Ph.D., P.E.Senior Consulting Engineer

www.enernex.com

APPA E&O Tech. Conf., April 16, 2007

APPA E&O Tech. Conf., April 2007 UWIG DistWind 2

UWIG’s DistWind Project

• Funded by APPA (DEED), NRECA (CRN), EPRI, California Energy Commission, others

• Web-based Screening Software Tools– Flicker evaluation– Economics

• Web-based Engineering Software Tools– Voltage control– Overcurrent protection

• Case studies, application guides, measurements


Distributed Wind Economics

• Capacity Factor: Determines Energy Production• Look at Wind as an Energy Source, not Capacity• Tax Incentives: Enhance the cash flow

– Production Tax Credit (PTC)– Clean Renewable Energy Bonds (CREB)

• Plus the usual considerations– Debt and Equity financing– Insurance, O&M, tax requirements– Evaluate by net present value (NPV), internal rate of

return (IRR), payback period, etc.


Production Tax Credit (PTC)

• Energy Policy Act of 1992 – 1.5 ¢/kWhr• Has been extended five times• Adjusted for inflation – currently 1.9 ¢/kWhr• Lasts for 10 years• Must pay federal income taxes in order to use

the PTC– Equivalent REPI for non-taxable entity, under-funded

• Tax Relief and Health Care Act of 2006– Extended PTC to December 31, 2008


PTC In WindFinance


Clean Renewable Energy Bonds• A “tax credit bond” for municipals, cooperatives, tribal

governments, others who can’t use PTC• Issuer pays no interest; instead the bondholder receives

a Federal tax credit• Energy Tax Incentives Act of 2005 authorized $800M for

CREBs issued in 2006 and 2007– 786 Applications Filed by April 26, 2006– 610 Approved; 112 for Wind and 434 for Solar

• Tax Relief and Health Care Act of 2006– Extended CREB another $400M (Total $1.2B)– Extended CREB to December 31, 2008


CREB In WindFinance


Capacity Factor

• Energy = CF * (8760 hrs/yr) * (kW rating)• Wind speeds are variable

– Power depends on speed3

– Actual site measurements are best

• Electrical power output depends on the turbine and interface design– Complicated function of aerodynamics and

controls– Controls are generally considered proprietary


http://www.nrel.gov/wind/wind_map.html


Economics: Capacity Factor Module

• Wind Data:– Actual Measured

Distribution– Measured

Average Annual Speed

– Average Annual Speed from a Map

• Power Curve:– Specific

• From Library• Uploaded

– Generic


What is Flicker?

• Short-term Voltage Fluctuations that may cause perceptible, or objectionable, lighting flicker

-200

-150

-100

-50

0

50

100

150

200

0.00

0

0.05

8

0.11

7

0.17

5

0.23

3

0.29

2

0.35

0

0.40

8

0.46

7

0.52

5

0.58

3

0.64

2

0.70

0

0.75

8

0.81

7

0.87

5

0.93

3

Time (s)

Vol

tage

(V

)

Vo

ltag

e C

han

ge

(in

Vo

lts)

on

120

V S

yste

m

Flicker Period [s]


What Causes Flicker?

• Motor starting and load variations

• Arc furnaces and welders

• Wind turbines– Variations in wind speed– Blade pitching– Tower shadowing– Wind shear or gradient– Start and stop


Variations in Wind Speed

• Inertia and controls help soften the impact

0

4

8

12

0 25 50 75 100

125

150

175

200

225

Time (seconds)

Win

d S

pee

d (

m/s

)

0

200

400

600

800

1000

1200

1400

Po

wer

(kW

)

generator output

wind speed


Effect of Blade Pitching• Pitch control affects power curve, but doesn’t respond instantly• Stall-regulated blades more closely maintain rated output

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0 2 4 6 8

10

12

14

16

18

20

22

24

Speed (m/s)

Ac

tiv

e P

ow

er

(kW

)

Pitch Regulated

Stall Regulated

Pitch Reg, Rated at 18 m/s


Tower Shadowing

• Sometimes called 3-P Effect, 0.5 – 1.5 Hz


Wind Shear or Gradient

• Blade torque varies with position because the wind speed varies with height

Wind Speed

Dis

tanc

e fr

om G

rou

nd


Turbine Start and Stop• Similar to motor starting, but advanced

controls and interface may soften the impact

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0 5 10 15 20 25 30

Wind Speed (m/s)

Po

we

r (p

er-

un

it)

Cut-in

Cut-out


Old-Style GE Curve• Rectangular Voltage Change,

50% Duty Cycle

-100

-50

0

50

100

0.0 0.1 0.2 0.3 0.4 0.5

Step-wise Flicker

Volta

ge M

agni

tude

(%)

Time (s)


Measurement is Complicated!

5010311.0 08.028.00657.00525.00314.0 PPPPPPst


Flicker Evaluation• IEEE Std. 1453-2004 follows the IEC approach• If PST = 1, 50% of the people will complain• Measured every 10 minutes (144 times per day) • Planning Level: PST > 0.9 only 1% of the time• Flicker varies along the feeder


Flicker Calculator• Quick Answers• On Web Site:

– NEG Micon– Nordex– Vestas– GE

• Requested:– Mitsubishi– Clipper– others


Estimating Short-Circuit Strength• Same Data as Used for Harmonic Studies• Estimate the System Impedance at Point of

Common Coupling (PCC) at Primary Voltage


Feeder Simulator for Engineering

• Imports MultiSpeak• Shortcuts• Sample Files• On-line Help


Voltage Control Outputs

Checks ANSI C84.1


Overcurrent Protection Outputs

CB1 should not lock open


Case Study #1: TVA Buffalo Mountain

• Three Vestas V47 WTGs, Total 2 MW• 13.2-kV Feeder, 9.6 miles long, 69-kV Source• No Voltage Control Problems• Removed the High-Speed Reclose Operation• No Reduction of Reach or Sympathetic Trip


Case Study #2: PGE Hunter’s Point

• 12-kV Feeder, 6.4 miles long• One GE 1.5xle Turbine, 1500 kW• Use high-efficiency turbine, greater hub height, and

higher wind shear factor than in CEC study• No Flicker Problems or Limits• Voltage Control and Overcurrent Protection limit the

total WTG to 7500 kW

0.9 miles 5.5 miles

Spot Load

115/12WTG

1500 kVAR


Case Study #3: Illinois Rural Electric

• One NM82 Vestas/NEG Micon Turbine, 1.65 MW• Operating since May 2005• 12.47-kV Feeder, 34.5-kV Transmission Source• IREC Filled out the Feeder Simulator Data Sheet• Overvoltage and Undervoltage Trip Functions are

Essential• Evaluated Use of CREB (actual project had 46%

grant funding, before CREB available)• Two Turbines → Flicker and Tap Changer Issues


East River Coop, Chamberlain, SD• Two Nordex N60/1300 Turbines• 69/12.47-kV Substation Transformer, 3750 kVA• 4/0 Cable, 1/3 Concentric Neutral, 12 kft from

Substation• On a Dedicated Feeder, but Still had Flicker

Complaints• Solutions implemented by Basin Electric:

– Turbine Vendor adjusted Controls– Dynamic VAR Compensation– Dedicated Transformer (2500 kVA Mobile)


Members-Only Index Page(www.uwig.org/distwind)

DEED members please contact Michele Ghosh Suddleson for password; [email protected]

Demos at the UWIG Booth in Vendor Showcase

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Assessing the Impact of Distributed Wind Generation

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