O

1
OM Cost Modelling, Technical Losses and
Associated Uncertainties

• Axel Albers
• Dipl.-Phys.
• Deutsche WindGuard Consulting GmbH
• Oldenburger Straße 65, D26316 Varel
• a.albers_at_windguard.d
• testing- and calibration laboratory with
• quality management system according EN ISO/IEC
  170252005

DAP-PL-3565.99 for power curve
measurements, wind measurements, wind resource
assessments
for power curve measurements
2
Contents

• Modelling of OM cost development in time
• Comparison of modelled OM cost with real wind
  farm data
• Development of WT availability in time
• Combination of uncertainties of wind resource,
  expected technical losses and OM cost

3
OM Cost Issues

• Questions
• 1. How large are maintenance and repair cost?
• 2. How do maintenance and repair cost develop
  with the age of WTs?
• Problems
• A) analysis of future OM-cost on component by
  component basis often impossible
• B) accurate public data on OM cost is rare
• C) only limited number of wind farms in high age
  (15-20a)
• D) rapid development of technology and size of
  WT in last decade
• Several studies show rise in QM-cost with WT age
  (BWE, WMEP, University of Durham and TU Delft)

4
Operational Costs by WT Age According to WMEP 2006
repair
maintenance
insurance
property
other
Warranty Period
operating year
Source WMEP 2006
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Rise of Repair and Maintenance Cost BWE 2002 Study

• In second decade cost twice as high as in first
  decade (BWE study 1999)
• 12 /MWh/a average cost over 20 years
  (corresponds to BWE 2002 numbers if 2000 full
  load hours are assumed), well in line with cost
  of most full service contracts
• Often assumed by wind farm developers or
  financiers
• - no rise with age
• - step functions after 10a or steps every 5th
  year

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Improved Approach for Rise in Repair and
Maintenance Cost

• There is no reason to assume a step function.
• Integrated cost increase in 2nd decade compared
  to 1st decade overtaken from BWE 2002 study
  (double cost in 2nd decade)

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Physical Model for Rise in Repair and Maintenance
Cost

• Damage increase per time is inversely
  proportional to remaining lifetime L-t
• - L total lifetime
• - t age
• Damage increase is proportional to increase of
  cost C

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Fit of Model for Rise of Repair and Maintenance
Cost to Observations

• In single years large outliers are observed, but
  the cumulated cost is fitted well by model.
• Always the same cost rise has been assumed (twice
  as much cost in 2nd decade than in 1st decade).

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Extrapolation of Repair and Maintenance Cost

• standard approach 0.012/kWh/a averaged over
  20a assumed (value from BWE-study 2002)
• Estimated standard uncertainty of standard
  approach 50 of modelled cost

10
Observations in Old Wind Farms In Respect to
Availability

• Experience based on
• - hundreds of WTs in age 12-20a in
  Eastern-Frisia (backyard of WindGuard)
• - due diligence in the frame of sales of wind
  farms
• - technical management of wind farms
• Availability normally high, but within year 5 to
  15 single events with long standstills likely
• One event with 3 months standstill leads to 2.5
  additional non-availability over 10 years
• Consequence 97 availability hardly possible in
  2nd decade in case of only a single extraordinary
  event

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Model for Increase of Availability Losses in Time

• The initialisation is treated case dependent
• - adjustment according to warranties or
• - adjustment according to availability of past
  operating period or
• - adjustment according to experience with wind
  turbine type

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Example for Increase of Availability Losses in
Time

• Model adjusted to observed non-availability
  losses in past (after initial project stage with
  teething problems)

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Combination of Uncertainties of Wind Resource
(Revenue) and OM-Cost

• Problem 1 The lower the wind resource, the lower
  the wear (repair cost)
• Solution
• i) calculate P50-value of OM-cost and standard
  uncertainty of OM- cost on the basis of Px-value
  of the production estimate
• ii) combine standard uncertainty of wind
  resource (revenue) and new standard uncertainty
  of OM-cost as independent uncertainties
• iii) consider normal distribution of difference
  of revenue and OM- cost with the combined
  standard uncertainty and calculate Px-value of
  this distribution

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Combination of Uncertainties of Non-Availability
Losses (Revenue) and OM-Cost

• Problem 2 increase of OM-cost with age highly
  correlated with increase of non-availability
  losses
• Solution
• combine standard uncertainty of OM-cost and
  standard uncertainty of revenue due to
  non-availability losses linearly

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Result of Combination of Uncertainties
moderate wind resource, high tariff
high wind resource, low tariff

• final result risk assessment of net earnings

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Conclusions

• Individual modelling of expected OM cost and
  availability over project lifetime is recommended
• Long-term OM cost often underestimated in
  planning phase
• - often about 85 EBITDA-margin expected over
  20a
• - latest study of BWE from 2009 76
  EBITDA-margin (average of 66 wind farms)
• Cost modelling often results in positive earnings
  even after 20 years
• Problem type certificate valid only 20 years
• - building permit of WT may lose validity
• - extension of type certificate to longer period
  in most cases not possible
• i) high cost
• ii) WT design often not conform with latest
  revision of IEC 61400-1