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Refining offshore wind turbine availability projections with latest operational experience and state-of-the-art modelling

The cornerstone of any successful offshore wind energy project is a robust assessment of the wind resource and energy yield. Indeed, with increasingly competitive auction driven markets, obtaining a robust and reliable pre-construction energy yield assessment of a proposed wind farm is paramount. Operating expenses can make up 30-40% of the overall cost of energy. We in DNV GL strongly believe that accurate energy yield assessments add credibility to the industry and so, we invest time regularly reviewing and validating our own methodologies. For offshore wind projects, that has included a recent refinement of our approach to estimating turbine availability projections as part of pre-construction energy yield assessments.

Besides wake losses, availability losses tend to be one of the largest contributing loss factors in an offshore pre-construction energy yield assessment. Whilst the key driver of availability in onshore wind turbines is turbine technology reliability, for offshore wind projects, access to the site and the wave climate are also significant contributors. In recent years, there has been an increase in the sophistication of access strategies and in vessel capabilities. These have served to improve accessibility to previously difficult to access far offshore sites, therefore reducing waiting downtime for necessary weather windows to perform any needed repairs or maintenance.

Historically, DNV GL’s approach to deriving a starting assumption for turbine availability in pre-construction energy assessments has been to broadly classify the offshore wind farm based on its distance to an operations and maintenance (O&M) port and the wave climate (benign, moderate or onerous). However, advances in offshore wind turbine technology and the increasing sophistication of project access strategies, which now includes helicopter access and Service Operation Vessels, offshore turbine availability is no longer limited by a project’s distance to the nearest O&M port or wave climate.

Considering this, we now apply a refined approach to estimating turbine availability in our offshore pre-construction energy yield assessments, thus bringing our projections in line with current industry experience. The approach is based on DNV GL’s in-house modelling tool, Optimisation of operation and maintenance (O2M) and supported by validations against real world data.

Developed and continually updated since 2005, DNV GL’s O2M model is a proven, industry leading model capable of modelling entire offshore wind farms, anywhere in the world. Developed using many years of purchased and publicly available information, the model draws on comprehensive databases of component failure rates and direct time to repair failures. Computer simulations have been run to capture a range of metocean conditions and O&M logistics which provide starting assumptions for an offshore wind farm’s turbine availability. This is based on key, high level inputs, such as the turbine technology proposed, metocean conditions and access strategy sophistication (e.g. Crew Transfer Vessels versus helicopter or Service Operation Vessels).

Given the relatively early stage of the wind farm development process when Pre-construction energy yield assessments are typically required, we appreciate that O&M and access strategies may not yet be fully developed. In these cases, we draw upon our extensive expertise and experience in all areas of offshore wind globally to make appropriate assumptions to inform a reasonable starting assumption for turbine availability in the context of a pre-construction energy yield assessment anywhere in the world.

The offshore wind industry has made significant progress in the last decade, transitioning into maturity and is now often viewed as a “new conventional”, rather than a challenger technology. Using a data driven approach to update its methodologies and keep pace with industry developments, DNV GL is well positioned to continue supporting the offshore wind industry, not only in the well-established markets in Northern Europe, but also the emerging and rapidly growing markets of North America, Taiwan, Japan, South Korea and China.

Please get in touch if there are any technical aspects of offshore wind farm development that you require support on!

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