Offshore wind - A safe investment! Developing best practice to avoid offshore wind farm yield over-prediction

Matthew Colls, Thomas Grey, Maria Cahill
Prevailing, Bristol, UK


Over the last eight years, Prevailing has predicted yield, or reviewed the analysis work of our peers at more than 1200 wind farms around the world.

For many of these projects, operational data provides the means to compare reality with prediction and assess current industry methods employed by Prevailing and other developers and consultancies.

Historically, many in the industry have been hurt by over-predicted pre-construction yield estimates, but in a highly competitive offshore investment environment with ever-slimmer margins, there is no room for inaccuracy.

In an engaging, data-fuelled presentation, Prevailing will draw on extensive experience to allow financial decision makers to understand where risks in modern yield assessment lie and show how they can be successfully mitigated.  Our newly completed validation study explains latest developments in offshore wind farm analysis techniques, outlines how historical biases have been identified and corrected, and discusses new risks arising as the offshore industry evolves in Europe and elsewhere.


The Prevailing study compares best practice preconstruction analysis with long-term operational project estimates for a number of European offshore wind farms.

Resource has been estimated using offshore mast data obtained from the Marine Data Exchange.  Long-term adjustment has been applied using both ground stations and MERRA2.

The UK Offshore Wind Resource Database, is used for local wind resource variation.  Gross energy yield is predicted using power curve data and industry best practice wake modelling, together with standard loss assumptions.

The validation was completed through comparison of these theoretical results with predicted operational long-term yield, using publically available production data.


The missing link is often perceived to be wind farm availability information. Prevailing has developed an innovative solution to obtain a like-for-like comparison of yield.



The output will show how close industry is to accurate offshore yield prediction using current techniques; highlighting areas of risk and suggesting methodology refinements.


As onshore wind matures, much more operational data has become available, revealing that pre-construction energy yield analysis methods applied across the industry, have resulted in optimistic predictions. With inaccuracies of several percent on average and up to 20% in certain cases, investor and lender confidence has been tested.


Applying lessons learned onshore, Prevailing seeks to guide the industry to avoid a similar outcome by critically appraising current offshore preconstruction yield methodology.


Investors and lenders, whose everyday role is to evaluate offshore wind farms, will leave with a clearer understanding of the flaws and risks inherent in current analysis methods, allowing more confident, better informed investment decision-making.

Energy yield practitioners will learn from Prevailing’s comparison of current techniques, enabling industry learning and best practice consensus.