Reactive Power Supplied by Wind Energy Converters CostBenefitAnalysis

1
Reactive Power Supplied by Wind Energy
ConvertersCost-Benefit-Analysis

• EWEC 2008, Brussels, Belgium
• 31 March 03 April 2008
• Martin Braun (ISET)

2
FENIX project (2005-2009)EC FP6 (SES6 518272)

• Development of the Virtual Power Plant Concept
• Integration of Distributed Generation and Loads
  in Electrical Power Systems
• Demonstration of Participation in
• Power Exchange Markets
• Balancing Markets (e.g. Tertiary Reserve)
• Reactive Power Supply
• Voltage Control
• etc.

3
Reactive Power Q An Introduction

• AC networks contain storage elements (inductors,
  capacitors)
• Reactive power oscillates between them
• Reactive power causes a phase shift between
  voltage and current
• Reactive power adds geometrically to active
  power
• Reactive power causes additional loading ?
  reactive power control is necessary for proper
  network operation
• Wind Turbines can be used for reactive power
  control

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Q
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4
Structure

• Reactive Power Control Capabilities
• Costs of Reactive Power Supply
• Cost-Benefit-Analysis
• Comparison with conventional reactive power
  supply technologies
• Comparison with network purchase costs of
  reactive power
• Comparision with benefits for network operation

5
Structure

• Reactive Power Control Capabilities
• Costs of Reactive Power Supply
• Cost-Benefit-Analysis
• Comparison with conventional reactive power
  supply technologies
• Comparison with network purchase costs of
  reactive power
• Comparision with benefits for network operation

6
Reactive Power Control Capabilities of
WECsGrid-Coupling Converters

• Directly-coupled induction generator (IG)? Q
  control only with capacitor banks? but
  capacitors network elements
• Directly-coupled synchronous generator (SG)? Q
  control possible? little installation rates

7
Reactive Power Control Capabilities of
WECsGrid-Coupling Converters

• Directly-coupled induction generator (IG)? Q
  control only with capacitor banks? but
  capacitors network elements
• Directly-coupled synchronous generator (SG)? Q
  control possible? little installation rates
• Doubly-fed induction generator (DFIG)? Q control
  possible
• Inverter-coupled IG/SG? Q control possible

8
Reactive Power Control Capabilities of
WECsGrid-Coupling Converters

• Directly-coupled induction generator (IG)? Q
  control only with capacitor banks? but
  capacitors network elements
• Directly-coupled synchronous generator (SG)? Q
  control possible? little installation rates
• Doubly-fed induction generator (DFIG)? Q control
  possible
• Inverter-coupled IG/SG? Q control possible

9
Reactive Power Control Capabilities of
Inverter-Coupled WECsReactive Power Capacity

• Fundamental LimitMaximum current transfer? max
  apparent power Smax
• Actual Limit Actual active power generation
  Pact(t)
• Actual reactive power capacity Qmax(t)

10
Reactive Power Control Capabilities of
Inverter-Coupled WECsReactive Power Capacity

• Fundamental LimitMaximum current transfer? max
  apparent power Smax
• Actual Limit Actual active power generation
  Pact(t)
• Actual reactive power capacity Qmax(t)
• Loading capability chart

11
Reactive Power Control Capabilities of
Inverter-Coupled WECsReactive Power Capacity

• Fundamental LimitMaximum current transfer? max
  apparent power Smax
• Actual Limit Actual active power generation
  Pact(t)
• Actual reactive power capacity Qmax(t)
• Loading capability chart

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Reactive Power Control Capabilities of
Inverter-Coupled WECsReactive Power Availability

• Enercon E-66 WEC
• Pnom 1300 kW
• ISET measurements
• 2001-2003
• Availability can beincreased by oversizing
• Guaranteed Q 0 kVar (1300 kVA)520 kVar (1400
  kVA)748 kVar (1500 kVA)

13
Structure

• Reactive Power Control Capabilities
• Costs of Reactive Power Supply
• Cost-Benefit-Analysis
• Comparison with conventional reactive power
  supply technologies
• Comparison with network purchase costs of
  reactive power
• Comparision with benefits for network operation

14
Costs of Reactive Power Supply

• Investment Costs /kVArdue to over-sizing ?
  guaranteed reactive power
• Operational Costs /kVArhdue to additional
  losses
• Additional Minor Cost Factors /kVArh
• Mechanical stress (electromagnetic forces)
• Thermal stress (higher temperatures)
• ? higher maintenance costs, equipment aging and
  unavailability
• ? mostly I²
• ? can be added to operational costs

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Costs of Reactive Power SupplyInvestment Costs

• Inverter investment costs 150 300 /kVA
• 12 oversizing leads to 50 guaranteed reactive
  power capacity

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Costs of Reactive Power SupplyOperational Costs

• Energy losses due to self-consumptionof the
  grid-side converter? efficiency

17
Costs of Reactive Power SupplyOperational Costs

• Energy losses due to self-consumptionof the
  grid-side converter? efficiency
• Calculation of Additional Losses by Reactive
  Power Supply

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Costs of Reactive Power SupplyOperational Costs

• Costs of energy losses 9 c/kWh

19
Structure

• Reactive Power Control Capabilities
• Costs of Reactive Power Supply
• Cost-Benefit-Analysis
• Comparison with conventional reactive power
  supply technologies
• Comparison with network purchase costs of
  reactive power
• Comparision with benefits for network operation

20
Structure

• Reactive Power Control Capabilities
• Costs of Reactive Power Supply
• Cost-Benefit-Analysis
• Comparison with conventional reactive power
  supply technologies
• Comparison with network purchase costs of
  reactive power
• Comparision with benefits for network operation

21
Cost-Benefit-AnalysisComparison with
conventional reactive power supply technologies

• Capacitor Banks
• Investment costs 15 /kVAr ( 20 /kVAr if
  reactors in addition)
• Compared with investment costs of WECs

22
Cost-Benefit-AnalysisComparison with
conventional reactive power supply technologies

• Capacitor Banks
• Investment costs 15 /kVAr ( 20 /kVAr if
  reactors in addition)
• Operational costs 1.5 W/kVAr ? 0.01 c/kVArh
• Compared with operational costs of WECs

23
Cost-Benefit-AnalysisComparison with
conventional reactive power supply technologies

• Static Compensators with Power Electronics (SVC,
  STATCOM)
• Investment costs 30-75 /kVAr
• Compared with investment costs of WECs

24
Cost-Benefit-AnalysisComparison with
conventional reactive power supply technologies

• Static Compensators with Power Electronics (SVC,
  STATCOM)
• Comparison of operational costs
• Only Q (STATCOM)
• Q and P (WEC with active power generation)

25
Cost-Benefit-AnalysisComparison with
conventional reactive power supply technologies

• Synchronous generators from conventional bulk
  power plants
• Synchronous generators one order of magnitude
  cheaper than inverters
• Losses are compensated at lower prices
• Normally operate at full load
• ? cheaper
• But WECs are distributed throughout the network
  ? more effective

26
Cost-Benefit-AnalysisComparison with
conventional reactive power supply technologies

• Synchronous generators from conventional bulk
  power plants
• Synchronous generators one order of magnitude
  cheaper than inverters
• Losses are compensated at lower prices
• Normally operate at full load
• ? cheaper
• But WECs are distributed throughout the network
  ? more effective
• Additional issues to be considered
• Compensation of Harmonics
• Short-circuit and overload behaviour
• Q dependency on bus voltage

27
Cost-Benefit-AnalysisComparison with
conventional reactive power supply technologies

• Synchronous generators from conventional bulk
  power plants
• Synchronous generators one order of magnitude
  cheaper than inverters
• Losses are compensated at lower prices
• Normally operate at full load
• ? cheaper
• But WECs are distributed throughout the network
  ? more effective
• Additional issues to be considered
• Compensation of Harmonics
• Short-circuit and overload behaviour
• Q dependency on bus voltage
• ? Conclusion
• Reactive power supply by WECs can often be
  cheaper
• than using conventional ways of reactive power
  supply

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Structure

• Reactive Power Control Capabilities
• Costs of Reactive Power Supply
• Cost-Benefit-Analysis
• Comparison with conventional reactive power
  supply technologies
• Comparison with network purchase costs of
  reactive power
• Comparision with benefits for network operation

29
Cost-Benefit-AnalysisComparison with network
purchase costs of reactive power

• German LV/MV network1.1 c/kVArh in average
  (0-2.7 c/kVArh) if power factor is below 0.9
• German HV network1.0 c/kVArh in average (0-1.5
  c/kVArh)
• National Grid UK0.2 c/kVArh
• US TNOs PJM, NYISO and ISO-NE
• Annual payment 0.75-4.4 /kVAra
• sometimes loss compensation 0.2 c/kVArh

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Structure

• Reactive Power Control Capabilities
• Costs of Reactive Power Supply
• Cost-Benefit-Analysis
• Comparison with conventional reactive power
  supply technologies
• Comparison with network purchase costs of
  reactive power
• Comparision with benefits for network operation

31
Cost-Benefit-AnalysisComparison with benefits
for network operation

• Voltage control? previous comparison showed
  use of WECs can be cheaper

32
Cost-Benefit-AnalysisComparison with benefits
for network operation

• Voltage control? previous comparison showed
  use of WECs can be cheaper
• Reduction of grid losses
• P const
• Costs in c/kVArh

33
Cost-Benefit-AnalysisComparison with benefits
for network operation

• Voltage control? previous comparison showed
  use of WECs can be cheaper
• Reduction of grid losses
• P const
• Costs in c/kVArh
• Reduction of congestions
• WECs are attractive to provide reactive power
  control
• BUT Presently, few congestions

34
Conclusions ofReactive Power Supply by WECs
Cost-Benefit-Analysis

• Costs of reactive power supply by WECs dependent
  on
• Oversizing ? requirements for guaranteed
  reactive power supply
• Operational point (P,Q) defines losses ?
  operational costs ? variable
• Benefits for network operation often higher than
  the costs? WECs attractive reactive power
  controllers

35
Conclusions ofReactive Power Supply by WECs
Cost-Benefit-Analysis

• Costs of reactive power supply by WECs dependent
  on
• Oversizing ? requirements for guaranteed
  reactive power supply
• Operational point (P,Q) defines losses ?
  operational costs ? variable
• Benefits for network operation often higher than
  the costs? WECs attractive reactive power
  controllers
• Less than 1 of the overall costs of a
  WECExample2-3 k/a for 1 MW WEC? 50 GW in
  Europe 100- 150 M/a? significant cost factor
  which should be minimized
• FERC 2005 inadequate reactive power leading to
  voltage collapse has been a causal factor in
  major power outages worldwide