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04 August 2012

There is a place for reducing the cost of offshore wind in the future, states naval architecture company KNUD E. HANSEN from Denmark

Article from Offshore Center Danmar by Russel James Brice

The Danish naval architecture and engineering company KNUD E. HANSEN has developed several special vessels for the offshore industry.

Offshore wind has been widely accepted as a viable means to harvest wind energy. The industry is now a developed market, where we see current and future projects with installation following quite similar practices. Will this situation lead to more economic project in the future? Is it also likely that offshore wind farm maintenance will be able to do the same?

Considering the current size of turbines the number of installations for an offshore wind farm is quite high. It is normal now to see 80-180 foundations. In good weather and optimized installation it is possible to install 1-2 foundations and 1-2 turbines per day. Depending on the installation method used, choice of vessel, logistic arrangement to supply port, it may be possible to feed the installation vessel offshore, and make full use of the available weather.

For most locations, operational weather limits relate to an installation opportunity of about 50%, depending on the site of course. If these rates are to increase, something in the current system needs to change. What is it that gives these limits and what can be done to improve the workability of the installation system?

Solutions available to implement

The cost of installation, other than the outright cost of foundations and turbines, is chiefly within the installation timeframe. The day rate cost of installation is generally fixed if the system is operational or sitting idle waiting for weather windows, so the key factors are:

  • Vessels that can operate in higher sea states
  • Work practices that allow safe operations in higher wind strength
  • Supply chain logistic that is robust.

There are solutions available to implement. Much of these solutions are affected via installation procedure design, while others concern the strategic use of advanced engineering techniques to validate safety measures, procedures and vessel operations.

Identifying functions

It is also possible to identify which equipment items are creating the operational limits and focus attention on either alleviating the use, choosing a different component or rearrange the procedure to shift the use off the critical path.

In cases where the operation calls for some novel equipment, KNUD E. HANSEN undertakes the process from the outset. The need is first analyzed to identify the basis functions which should be performed. Complete systems developed and executed to date consist of; numerous seafastening arrangements, substation transition piece transport (including J-tubes) & installation, reconfigurable deck arrangements for project service barges, ship to ship transfer systems for monopiles, dynamic heave compensated upending shoe for monopiles. It may well be that a standard method is used more out of industry expectation rather than good common sense. These are the points which need to be addressed as early as possible. The increased operational limits will translate into schedules under less time pressure and a quicker installation period.

Focus on the on-going service cost

This approach is also suitably applicable to wind farm maintenance. The on-going service cost of the wind farm is in need of attention. Installation vessels are far too expensive for use as maintenance and transport. It is likely that maintenance programs will run for longer periods of time, requiring greater accommodation and attention to differing operational profiles.

KNUD E. HANSEN has developed several concepts which aim to meet the variation of requirements set by the maintenance need. Periodic maintenance and replacement of small items, inspections etc… require far more personnel transfers that that of large component replacement and service. The solutions require dramatically different functional approaches which are able to work both in parallel and individually. Again the key factors are:

  • Vessels that can operate in higher sea states
  • Work practices that allow safe operations in higher wind strength
  • Supply chain logistic that is robust

Realization of these objectives for a regular maintenance solution results in a different set of vessel design criteria. In this case a robust supply chain could mean the capability to take on board replacement equipment and resupply the vessel at sea. Operations in higher sea states will principally involve transferring personnel.

Related References

Wind Turbine Installation vessel
  • Vessel name: Pacific Orca & Pacific Osprey
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