Risk-based maintenance planning of offshore wind turbine farms

Significance 

A wind farm is composed of a group of wind turbines situated in a given location to produce electricity. Wind farms vary in size from a small number of turbines to several hundred wind turbines covering an extensive area and can be either located onshore or offshore. An onshore wind farm is a capital-intensive project due to high wind turbine cost, which may account for a large majority of the total life-cycle cost. As far as an onshore wind farm is concerned, the operational cost involved is also an important part of the overall cost due to costly inspection and maintenance actions for support structures as these actions require specific training and equipment fit for the offshore environment. As the bottom fixed offshore wind technology is already considered as a proven technology, the offshore wind farms are planned to be built in greater size with more powerful offshore wind turbines to make the offshore wind energy more cost-effective, which leads to more significant capital investment. Moreover, increasing the size of offshore wind farms has consequences not only from a capital investment point of view but also from an operational cost point of view because large-scale offshore wind farms with a higher number of support structures to be inspected increase the operational cost.

In essence, there is a need for constant monitoring of the structural condition of the support structure through scheduled inspections. This enables decision-makers to have better information about the structural safety and more confidence in the success of the offshore wind turbines support structure fulfilling its service purpose, allowing investors to achieve better management of the investment risk. Still, the need remains for refinement of analysis techniques for better projections. On this account, Centre for Marine Technology and Ocean Engineering, Instituto Superior Técnico, University of Lisbon researchers: Dr Baran Yeter, Professor Yordan Garbatov and Professor Carlos Guedes Soares developed a risk-based maintenance planning for offshore wind farm installations. They aimed to find the optimal number of offshore wind turbines in an offshore wind farm, resulting in the minimum life-cycle cost per produced energy. Their work is currently published in the research journal, Reliability Engineering and System Safety.

In their approach, the research team considered an offshore wind farm consisting of correlated components. The system reliability was then estimated using the Ditlevsen bounding technique, which is based on a time-variant correlation matrix of offshore wind turbines. The researchers then employed the event tree method to assess the expected cost of failure to be included in the capital investment as the structural risk premium and the total expected cost as a part of the operational cost.

The team reported that the developed framework was able to connect the results of the risk assessment with both CAPEX and OPEX, and the number of offshore wind turbines to be installed in an offshore wind farm was estimated. Following this, the minimization of the levelized cost of energy was adopted as an objective function. Overall, the optimal number of monopile offshore wind turbines to be installed in an offshore wind farm was estimated as 60.

In summary, the Centre for Marine Technology and Ocean Engineering, Instituto Superior Técnico, Lisbon University study presented a framework to conduct a life-cycle cost assessment accounting for the optimal inspection and maintenance policy to be implemented. A case study was performed using the developed framework, where outstanding results were successfully achieved. In a statement to Advances in Engineering, the authors explained that the presented framework in the paper involves an intricate network of a structural risk assessment, inspection planning, and life-cycle cost assessment; therefore, the initial assumptions regarding some cost components may impact the final results since the difference between the offshore wind farms with a different number of offshore wind turbines is relatively low.

Risk-based maintenance planning of offshore wind turbine farms - Advances in Engineering Risk-based maintenance planning of offshore wind turbine farms - Advances in Engineering Risk-based maintenance planning of offshore wind turbine farms - Advances in Engineering

About the author

Dr Baran Yeter is a researcher in the Marine Structures research group of the Centre for Marine Technology and Ocean Engineering (CENTEC). He has been involved in many research projects funded by national and international organisations. He obtained his BSc degree in Naval Architecture and Ocean Engineering from the Istanbul Technical University, Turkey, in 2011. He obtained his MSc degree in 2013 and PhD in 2020 in Naval Architecture and Ocean Engineering from Instituto Superior Técnico, the University of Lisbon, Portugal. He has co-authored 27 papers (https://scholar.google.pt/citations?user=gEs-wQ4AAAAJ&hl=en ).

Since 2017, he has been conducting extra activities as a part of the scientific committee of international journals such as Ocean Engineering, Engineering Structures, Wind Energy, Ship and Offshore Structures, and international conferences such as the International Conference on Ocean, Offshore and Arctic Engineering. His main research interests include fatigue, fracture mechanics, marine structures, offshore wind, reliability, risk-based maintenance, corrosion, life-cycle analysis, data analytics and machine learning, engineering economics and corporate finance.

About the author

Prof. Yordan Garbatov is a Professor in Naval Architecture and Marine Engineering at the Engineering Faculty (Instituto Superior Técnico) of the University of Lisbon. He has graduated from the Technical University of Varna, Bulgaria, in 1986 and received his PhD from the Technical University of Lisbon in 1998 and his Doctor of Science degree from the University of Lisbon, Portugal, in 2013. Prof. Garbatov is the President of the Centre for Marine Technology and Ocean Engineering (CENTEC). He actively contributed to establishing fruitful scientific collaborations with international reference centres, and he has been involved in 18 EU R&D Projects.

He published more than 140 papers in journals related to fatigue and fracture mechanics, structural degradation, progressive collapse, welding simulation and analysis, structural reliability, and risk-based maintenance of ships and offshore structures (https://www.scopus.com/authid/detail.uri?authorId=12784798500). He is deeply involved in the editorial process in the Journal of Ocean Engineering, Journal of Offshore Mechanics and Arctic Engineering and Journal of Oceans, and in the organisation of several international conferences.

About the author

Prof. Carlos Guedes Soares is a Distinguished Professor of the Engineering Faculty (Instituto Superior Técnico) of the University of Lisbon and the Scientific Coordinator of the Centre for Marine Technology and Ocean Engineering (CENTEC), which is a research centre of the University of Lisbon, rated as “Excellent” and funded by the Portuguese Foundation for Science and Technology. He received the Masters and Ocean Engineer degrees from the Massachusetts Institute of Technology, the USA, in 1976, the PhD degree from the Norwegian Institute of Technology of the University of Trondheim in 1984, and the Doctor of Science degree from the Technical University of Lisbon, Portugal, in 1991. He has supervised more than 55 PhD students and has co-authored more than 700 journal papers.

He has been publishing on probabilistic modelling, uncertainty analysis, reliability and maintenance, applied to different problems. He is a Fellow of SNAME, RINA, IMarEST, ASME, Ordem dos Engenheiros, Member of ASCE, AGU and SRA and a Member of the Portuguese Academy of Engineering. He has been involved in the organisation of several Conferences, particularly on Renewable Energies Offshore, the last of which was RENEW2020 (http://www.centec.tecnico.ulisboa.pt/renew2020/), https://www.cienciavitae.pt/portal/en/411E-B911-1D2A.

Reference

B. Yeter, Y. Garbatov, C. Guedes Soares. Risk-based maintenance planning of offshore wind turbine farms. Reliability Engineering and System Safety; volume 202 (2020) 107062

Go To Reliability Engineering and System Safety

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