Wind Farms in a Gross Pool Market: Specific issues for wind farms

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Wind Farms in a Gross Pool MarketSpecific
issues for wind farms
Perspectives from AbroadSustainable Energy
Ireland, Dublin 13 June

• Hugh Outhred
• School of Electrical Engineering and
  Telecommunications
• The University of New South Wales
• Sydney, Australia
• Tel [phone] Fax [phone]
  Email h.outhred_at_unsw.edu.au
• www.ergo.ee.unsw.edu.au

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Outline

• Trends in wind energy
• Network-related issues
• Power variability issues
• Forecasting wind farm output
• Spot derivative markets
• Are wind farms viable in the National Electricity
  Market?

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Wind turbine installations in Australiahistory
forecast
Summary of wind farm projects at 3/03.
Approximate, based on www.auswea.com.au
Completed 105 MW
Under Construction 106 MW
Tendering 230 MW
Approved 294 MW
Planning 1400 MW
Total 2135 MW
(AusWEA IEA Annual Report, 2002)
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Australian wind farm planning experience to date

• Limited experience to date
• Some strong support, some strong opposition
• Mixed federal, state local government approvals
  process lacks coherence
• Project based - may not manage cumulative issues
  interactions well
• Other industries have a comprehensive planning
  framework, eg
• Strong, state-based planning framework for the
  minerals industry

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Network issues for wind farms 1

• Networks are shared, centrally planned resources
• Must limit disturbances caused by wind farms
• Must survive disturbances from the network
• Renewable resources are often distributed
  differently from fossil fuel resources
• Weak network conditions likely to be more common
  in Australia than Europe or North America
• Network must be built to carry peak flows
• Want good estimates of aggregation seasonal
  effects
• Benefits of staged development of wind resources
• Network savings reduced voltage frequency
  impacts

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Network issues for wind farms 2

• Wind turbine starting stopping transients
• Severity can be alleviated by soft-start high
  wind-speed power-management
• Some wind turbine designs
• May cause voltage distortions
• Harmonics /or transients
• May have poor power factor, eg
• Uncompensated induction generator
• May not ride-through system disturbances
• Temporary voltage or frequency excursions

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Wind turbine type comparison(Slootweg Kling,
TU Delft, 2003, http//local.iee.org/ireland/Senio
r/Wind20Event.htm)
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Size of wind turbines used by Western Power
(www.wpc.com.au)
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Wind turbine starting transients for Esperance 2
MW wind farm

• 9 x 225 kW turbines with squirrel cage IG
• Magnetisation inrush current may cause a voltage
  dip - starts should be spaced out
• (Rosser, 1995)

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Network connection issues examples

• Approximate ability of a transmission line to
  accept a wind farm
• 66kV 20MVA
• 132kV 100MVA
• 330kV 200MVA
• Constraints may be determined by several factors
• Thermal, voltage, fault clearance, quality of
  supply
• Thermal ratings depend on line temperature wind
  speed
• Relevant wind farm rating is its maximum output,
  not the sum of turbine rated powers
• Coincident output of the connected wind turbines

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Connection costs to 330kV(Transgrid, 2002)
Wind farm number Total wind MW Conn. cost M Conn.cost /kW
1 5 12.7 2,500
1 20 12.9 650
2 100 17.7 180
4 200 28.3 150
Important to capture economies of scale of grid
connection
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NEMMCO concerns about wind energy (NEMMCO, 2003)

• Frequency control in normal operation
• Frequency regulating service costs 5 /MWH
• Security control - largest single contingency
• Will wind farms ride-through disturbances?
• Interconnection flow fluctuations
• Exceeding flow limit may cause high spot price
• Forecast errors due to wind resource uncertainty
• Five minute dispatch forecast (spot price)
• Pre-dispatch longer term (PASA SOO) forecasts

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Western Powers proposed wind penalty charge
(c/kWh) (Western Power, 2002)
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Demand forecast errors South Aust,02 Q4 (NECA,
02Q4 Stats, 2003)
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Spectral analysis of Danish long-term wind data
(17 years of data)
Spectral gap between weatherand local turbulence
phenomena
(Sorensen, 2001, Fig 2.110, p194)
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Forecasting the output of wind farms

• 30 minute horizon (FCAS spot market)
• Turbulence spectrum - likely to be uncorrelated
  for turbines spaced gt 20 km
• Then power fluctuations N-0.5
• eg for 100 identical wind farms spaced gt20 km
  apart, fluctuation in total power
  0.1xfluctuation for 1 farm
• 30 minutes to 3 hours
• ARMA model best predictor of future output
• gt 3 hours
• NWP model best predictor

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One-second power fluctuations at Esperance 2MW
wind farm

• 9 x 225 kW turbines
• Solid line is proportional to N-0.5
• Implies 1-second fluctuations are uncorrelated
• (Rosser, 1995)

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Forecasts for Lake Benton wind farm, USA138
turbines, 103.5MW, hourly data (Hirst, 2001)
Two-hour ahead prediction of wind
power MWPred(T2) 2.7 0.9xMW(T) MW(T) -
MW(T-1)
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Combined output of 2 wind farms 80 km apart
(Gardner et al, 2003)
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Cross-correlations between measured power outputs
of German wind farms
(Giebel (2000) Riso National Lab, Denmark)
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Cross-correlations between 34 years of 12-hourly
data for all grid points
(Giebel (2000) Riso National Lab, Denmark)
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CSIRO WindscapeTM model (www.clw.csiro.au/products
/windenergy)
Windscape derives location-specific wind
forecasts from a Numerical Weather Prediction
model

(Steggle et al, CSIRO, March 2002)
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(Steggle et al, CSIRO, March 2002)

• Windscape predictions of annual mean wind speed
  at 65 m, showing nested model results
• More rapid changes in colour probably imply
  higher local turbulence

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SEDA NSW Wind atlas(www.seda.nsw.gov.au)
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Issues for NEM spot market

• Wind farms will operate as price takers
• Generate whenever wind is blowing
• NEM spot market prices are volatile with a
  rectangular price distribution
• Prices are usually low, sometimes high
• Timing of high prices not easily predicted
• Value of wind energy in the spot market
• Will depend on how regularly wind farms are
  producing when spot prices are high

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1GW wind contribution to meeting SA
Load(simulation study)
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Spot price as a function of demand SA,02 Q4
(NECA, 02Q4 Stats, 2003)
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Weekly average NEM spot prices since market
inception (NECA, 02Q4 Stats, 2003)
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Forward prices for wind energy

• Wind farms may have to accept a lower price than
  flat contract due to uncertainty in production
  
• Daily
• Seasonal,
• Annual

(Giebel (2000) Riso National Lab, Denmark)
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Flat contract prices, 1999-2006 (NECA, 02Q4
Statistics, 2003)
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Renewable Energy Certificate Prices (A/MWH)
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Wind farms marginal at 70/MWH(PWC, 2002)