Weather window analysis for ocean energy devices: case study off the west coast of Ireland

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Weather window analysis for ocean energy devices
case study off the west coast of Ireland
Dr. Gordon DaltonHMRC, UCC, IrelandCharles
Parsons research fellowandMichael OConnor
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Case study objectives

• Quantify the levels of access due to weather
  windows that exist off the west coast of Ireland
  for offshore wind and wave energy.
• Implications for installation and
  operations/maintenance
• Technical impacts
• Economic impacts

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What is a weather window?

• A weather window occurs when a weather forecast
  indicates that a given set of marine operations
  can be performed within their maximum limits of
  their appropriate constraint i.e. wave height in
  this case study.
• Weather windows are dependant
• Time needed eg 6 hours etc
• Wave height for Access
  1m

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Wave height max for access forOffshore Repairs
Transport Type Wave Height Limit Hs Wind Speed Limit m/s
Wave Energy Converter Conventional Vessel Assumed to be 1m or less.
Offshore Wind Turbine Conventional Vessel 1.5m 12 m/s
Offshore Wind Turbine Helicopter Transfer Not Applicable 15 m/s
Offshore Wind Turbine Catamaran 1.5 2.0m 12 m/s
Offshore Wind Turbine SWATH Vessel 2.5m 12m/s
Offshore Wind Turbine Ampelmann 3.0m
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Max wave height for Onshore repairsMaintenance
not-involving personnel transfers (device brought
ashore or maintained aboard large support vessel)
Vessel Wave height Wind speed
Offshore Navigation or Data Buoys Tender Vessel 2.5m 8-10 m/s
Wave Energy Converter (Pelamis) Tug 2.0m Not Applicable unless Maintenance involves cranes
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Case study location

• Years 2003 - 2005
• Data obtained from HMRC and Marine Institute
  (MI).
• Data Location M1M3 Buoy, 50 km off west coast
  of Ireland, 150m depth.

M1M3 Buoy
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Wave energy economic model - NAVITAS

• Model created in HMRC and funded by Charles
  Parson award for post-doctoral research.
• Two stage assessment
• Resource assessment.
• Economic feasibility analysis using standard
  economic indicators.

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Results- Average power in the wave

• M1, 20 stronger wave power than M3, 2 out of 3
  years.
• M1, 45 variation in wave power between 2003 and
  2004.

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Annual mean exceedance

• 70 of the wave height incidence is above 2.0m
• In general M1 has higher waves than M3.

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Wave heights as a of total wave regime

• Greatest frequency of wave height between 1m-3m.
• M3 slightly lower peak wave height frequency than
  M1

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Accessibility - of the year

• Irish and North Sea worst case scenarios (Hs 1m)
  to the best case scenario (Hs 2.5m) off the
  west coast of Ireland. 45

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Hours of wave height below limit for M1
  Annual hours of year
1m 210 2
1.5m 1130 13
2m 2380 27
2.5m 3880 45
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Accessibility and occurrence by window length
  M1 M1 M1 M1 Columbia River Bar Columbia River Bar Columbia River Bar Columbia River Bar
2.5 43 41 38 31 62 61 58 53
Hs (m) 2 26 24 21 15 45 45 42 36
1.5 12 10 9 5 25 24 21 14
1 2 2 1 0 5 4 3 1
  6 12 24 48 6 12 24 48
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Annual Number of Windows

• At 2.5m limit, many windows, even at 48 hours
  long
• At 1m limit, only 8 windows for 6 hour window and
  zero for 48 hour window

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Weeks between windows

• At 2.5m limit, short wait, 10 weeks, even at 48
  hours long
• At 1m limit, 30-40 week wait, 6-24 hour window. 3
  years or more for 48 hour window

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Conclusion for 1m wave height

• Accessibility 2 of the year, compared to 40 in
  Irish sea and North Sea.
• 80 hours total access in summer, 0 in winter.
• lt 10 windows per year, 6 hour window or greater.
• gt 30 week wait between windows, 6 hour window or
  greater.

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Implications for O/M

• Devices will need to have
• wave height access limits as high as possible,
• O/M duration as short as possible and
• time between maintenance as long as possible.
• If possible, devices exchanged and repaired
  onshore rather than maintaining devices offshore.
• Greater improvement is achieved by increasing
  access limit over decreasing O/M duration.
• If the advanced access system such as the
  Ampelmann could be used, it would raise access
  limit to 2.5 to 3m.

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Future research work Resource

• Period, wind speed, tidal flow, freezing
  temperatures
• Comparison to Portugal and Scotland

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Future research work - economics

• Rigorous assessment of installation and O/M costs
  and impact of weather windows on COE and NPV
• At present costs for installation and O/M are
  calculated approximately as either
• of Capex
• A nominal /kWh based on other work.

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Methodology Installation O/M

• Installation Economic impacts are through
• Extended vessel and person hire
• Delay in start of energy production
• O/M Economics impacts are due to
• on number of hours required for scheduled and
  unscheduled O/M, downtime and consequent loss of
  energy production.
• Costs Barges, vessels, cranes etc.
• Costs Materials, spares etc
• Person hours
• Hours available for the job

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• Thank you