Addressing the challenges of offshore wind turbine installation and maintenance in high winds

Turning weather risks into a window of opportunity

To improve profitability, offshore wind farms are moving further offshore and significantly growing in size. The latest example is the 1200 MW Hornsea project, located 120 kilometres off the UK coast with more than 170 turbines.

With further offshore locations, more severe weather conditions follow, particularly with respect to wave and wind conditions. Far-shore offshore wind sites in the German North Sea have wind average wind speeds of 10+ meters per second.

From an energy generation perspective, these conditions are excellent. The flip side of the coin is however that the conditions can present a significant challenge during installation and weather remains a critical factor for the project’s success.

Since weather always “occurs”, the question is not so much if there will be weather downtime, but rather what is the probability of achieving the scheduled completion date for the respective activity and the project as a whole?

To minimize risks, comprehensive planning, preparation, robust project and risk management must be applied. In this respect, quantitative cost and schedule risk assessment can be used to size specific weather risk contingency amounts to be included in the construction budget and overall contingency for the project. Furthermore, it is important that all stakeholders are upfront, transparent and realistic in terms of the risks, only then can it also become an opportunity.

With the right combination of technical innovation, different contracting strategies and robust, state of the art risk management tools and approaches we can substantially reduce the cost of offshore wind.

Mapping risks

To reduce any risk you have to fully understand it. The same applies for weather risks, which are extremely complex and multifaceted. Project location, metocean conditions as well as project specific installation setup have to be thoroughly analysed.

Jacking operations may be limited by significant wave heights. Once jacked up, wind speed typically becomes the more critical factor, whereby other elements such as visibility may also play a role.  Additionally, requirements of the Marine Warranty Surveyor, domino effect etc. must also be factored in.

For the wind turbines, the installation of the blades is typically the most critical operation, with the most strict weather limits. Years ago, some projects used a full rotor star installation with wind speed limits of 8-10 m/s. This resulted in vessels being on stand-by for days or even weeks to find a suitable weather window.

Today, single blade installation is the only realistic option for turbines with blades of 75 meter and more. If installation can be done at 12 or even 14 m/s weather delays for this activity will be significantly reduced.

Several tools have been developed within the industry to analyse weather risks and if the limitations for each aspect of the installation can be quantified in sufficient detail, then it is possible to conduct statistical analysis using long term metocean data and derive robust estimates at different confidence levels. 

Installation trends

Wind turbine manufacturers and third parties are developing tools and installation equipment to allow them to install components, including large blades, at higher wind speeds. This will allow quicker installations, but also increase suitable weather periods throughout the year.

Fall and winter are now interesting installation periods. Large projects, which for example can’t be installed in one summer season, expand to other seasons or multiple installation vessels are hired to take full advantage of periods with good weather.

From a contractual perspective, there has been a general trend in the industry to push as much as possible weather risk across to the contractors. This provides cost certainty to a degree, but it clearly comes with a high premium and increases the cost for the project with limited or no access to the upsides should the weather be better than expected. If you are trying to lower the overall project costs this is counterproductive.

This approach has, however, backfired on some historic projects, when the contractors underestimated the risk, either due to lack of knowledge or deliberately in order to win the job during the tendering phase, causing significant problems during the project execution.

Today, we see a number of developers that are considering to take on more weather risks at a project level to reduce costs. It is however absolutely critical that this is done in a robust manner. Underestimating risks could be very harmful for the project itself and undermine the general, current trust in the offshore wind sector.

Remember the basics

A schedule risk analysis is inevitable and unfortunately still too often overlooked in the industry. Program dates are simply treated as pre-determined values, although they are subject to uncertainty.

To successfully manage weather risk at a project level you have to fully understand:

  • The schedule risks for each package
  • The buffer between the packages and their interaction
  • The critical path of the project
  • The robustness of the overall program in case of disruptions

Furthermore, clear and unambiguous adverse weather regulations are needed in the contracts and comprehensive control and monitoring processes need to be in place during execution. A transparent and up-front approach between the Employer and Contractor is critical to ensure buy in to the approach from all stakeholders. Critical aspects must be addressed and solved, i.e. how to deal with employer and contractor caused delays and securing of vessels for the required timeframe.

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