This paper investigates the relationship between wind turbine main‐bearing loads and the characteristics of the incident wind field in which the wind turbine is operating. For a 2‐MW wind turbine model, fully aeroelastic multibody simulations are performed in 3D turbulent wind fields across the wind turbine's operational envelope. Hub loads are extracted and then injected into simplified drivetrain models of three types of main‐bearing configuration. The main‐bearing reaction loads and load ratios from the simplified model are presented and analysed. Results indicate that there is a strong link between wind field characteristics and the loading experienced by the main bearing(s), with the different bearing configurations displaying very different loading behaviours. Main‐bearing failure rates determined from operational data for two drivetrain configurations are also presented.

This paper considers the time-varying loads experienced by wind turbine main bearings. Radial load trajectories based on simulated data indicate that 'looped' structures, in the form of repeating changes in radial load magnitudes and directions that form elliptical patterns, are present, which have not been described before in the literature. In order to allow these identified structures to be described and studied, an automated method for identification and parameterisation of these loops is presented, along with preliminary results from applications on simulated data. In order to assess the relative importance and potential impacts of these identified structures on bearing rollers, an internal load model for double-row spherical roller bearings is also developed. Results indicate that identified loops in radial main bearing applied loads lead to significant fluctuations in bearing roller loads, even within normally unloaded regions. These findings motivate further study with respect to the identified load structures and their impacts on wind turbine main bearing internal loading and failures. The methods developed in this paper provide the basis for a systematic approach and necessary tools for this future work.

This paper presents a review of existing theory and practice relating to main bearings for wind turbines. The main bearing performs the critical role of supporting the turbine rotor, with replacements typically requiring its complete removal. The operational conditions and loading for wind turbine main bearings deviate significantly from those of more conventional power plants and other bearings present in the wind turbine power train, i.e. those in the gearbox and generator. This work seeks to thoroughly document current main-bearing theory in order to allow for appraisal of existing design and analysis practices, while also seeking to form a solid foundation for future research in this area. The most common main-bearing setups are presented along with standards for bearing selection and rating. Typical loads generated by a wind turbine rotor, and subsequently reacted at the main bearing, are discussed. This is followed by the related tribological theories of lubrication, wear and associated failure mechanisms. Finally, existing techniques for bearing modelling, fault diagnosis and prognosis relevant to the main bearing are presented.Published by Copernicus Publications on behalf of the European Academy of Wind Energy e.V.

Abstract. This paper is the first in a two-part study on lubrication in wind turbine main bearings. Elastohydrodynamic lubrication is a complex field, the formulas and results from which should not be applied blindly, but with proper awareness and consideration of their context, validity and limitations in any given case. The current paper, “Part 1”, therefore presents an introductory review of elastohydrodynamic lubrication theory in order to provide this necessary background and context in an accessible form, promoting cross-disciplinary understanding. Fundamental concepts, derivations and formulas are presented, followed by the more advanced topics of starvation, non-steady effects, surface roughness interactions and grease lubrication. “Part 2” applies the presented material in order to analyse wind turbine main-bearing lubrication in the context of available film thickness formulas and related results from lubrication theory. Aside from the main-bearing, the material presented here is also applicable to other lubricated non-conformal contacts in wind turbines, including pitch and yaw bearings and gear teeth.

Since Vindeby in 1991, more than 100 projects have been installed in Europe, and will need decommissioning one day. Despite the increasing number of projects reaching this phase, decommissioning is still an area that has received relatively little attention. This paper considers the practicalities and economic implications of recycling offshore wind components as part of an end of life strategy. There is no existing source that gathers together materials data for currently operational wind turbines in Europe relevant to recycling. Since this information is necessary for any economic analysis of component recycling, such a dataset was generated. The results illustrate the specific wind turbine materials suitable for recycling, expressed in percentage values of the wind turbine's total mass. An economic analysis is then performed to study how recovering these materials and selling them as scrap metal can impact the decommissioning costs. As concluding remarks, recycling offshore wind components could pay for nearly 20% of the total wind farm decommissioning costs if monopile foundations are considered. Furthermore, the volatility of scrap prices is such that this could even help define when it would be best to decommission an offshore wind farm. COVER LETTERThank you very much for considering our article. It has a lot of effort with diverse expertise from people with different backgrounds. It is a topic that is currently receiving a lot of attention and causing concerns, and is the first outcome of a wider research we are producing.We are proud of submitting it to Energy Policy as we consider this journal is ideal for generating the corresponding concerns and in consequence, enable a transition to a potential improvement and make this end of life stage, more sustainable. Cover LetterTitle page HIGHLIGHTS  Uncertainties in end of life strategies of offshore wind projects make decisions complex and challenging  An inevitable decommissioning era is arriving which must adequate to project's characteristics  Recycling should be included as a target and taken into consideration since the planning  An appropriate recycling could pay part of the decommissioning costs while making the process more sustainable  The volatility of scrap value can help determine when it is best to decommission *Highlights Response to Reviewers1 ABSTRACT Since Vindeby in 1991, more than 100 projects have been installed in Europe, and will need decommissioning one day. Despite the increasing number of projects reaching this phase, decommissioning is still an area that has received relatively little attention.This paper considers the practicalities and economic implications of recycling offshore wind components as part of an end of life strategy. There is no existing source that gathers together materials data for currently operational wind turbines in Europe relevant to recycling. Since this information is necessary for any economic analysis of component recycling, such a dataset was generated.The results illustrate the specific wind turbine...