Cost Effective Ways of Offshore Wind O&M Examined at University of Stavanger

Statoil has accepted to support a PhD work of Ole-Erik Vestøl Endrerudat at University of Stavanger with Dr. Nenad Keseric from Statoil Wind Operations being a co-supervisor. The PhD work examines ways to the most cost effective operation and maintenance of offshore wind farms.

Statoil wind operation department has recognised the potential of the agent-based model developed during first phase of the PhD and proposed to utilise it for decision analysis on the Dudgeon wind farm as a test case.

The purpose of the decision analysis was to compare and give indication on most cost-efficient marine logistic solution for Dudgeon wind park with given historical weather pattern. Two advanced vessel solutions and a conventional personnel transfer vessel (PTV) solution were analysed with aim to provide a sound basis for deciding which one of these solutions are most suited to meet the desired regularity, cost and risk.

The life cycle cost of such a facility is very large and is a financial risk for investors, and with 25-30% of that being costs related to operation and maintenance, reducing this cost is a prime factor for mitigating financial risk. In collaboration with Statoil operation and maintenance (O&M) department, a new marine logistics solution for offshore wind parks was analysed and suggested consisting of two innovative vessel solutions (surface effect ship (SES) and service operation vessel (SOV)) that are quite unique and new to the offshore wind industrial sector.

Following a successful partnership developing the Sheringham Shoal Offshore Wind Farm off the coast of North Norfolk in UK, Statoil and Statkraft are working together on developing the Dudgeon Offshore Wind Farm, of which Statoil will be the Operator for both the construction and operational phases. Offshore construction will start in 2016 and the project aims for full production in 2017. Dudgeon Offshore Wind Farm will be constructed with 67 wind turbines, each with a capacity of 6 MW, totalling 402 MW installed generation capacity.

Methodology

A decision methodology based on simulation modelling and analysis was selected due to the large uncertainties inherent in the new vessel solutions, and the fact that only a simulation model could take into account the complexity (in terms of stochasticity, variability and time dependency) of operating and maintaining an offshore wind park. Endrerud has developed such a model and further documentation can be found in Endrerud, Liyanage and Keseric (2014 (in press)) and Endrerud and Liyanage (2013 (in press)). The model have been verified, and to the extent possible validated, in a joint study between University of Stavanger, Sintef, EDF Energy and University of Strathclyde, from which the results were reported in Dinwoodie et al. (2014 (submitted for review)).

The model was first configured to fit the O&M and marine logstics system of Dudgeon Wind Park, a task performed in collaboration with Statoil Wind O&M department. Followed by several simulation experiments with the different decision alternatives, ranging from only PTVs, only SESs, a combination of the former two with an SOV and only an SOV. The results were analysed to see if the decision alternatives were statistically significant from each other based on hypothesis testing. In case they were, further analysis was conducted to identify the root cause of the differences.

Conclusion

The main conclusions from the study were that a solution with conventional PTVs and an SOV for offshore accommodation and access during rough weather periods were the most optimal solution when including the technological readiness level of the different decision solutions. However, the analysis also discovered that for offshore wind parks at distances from shore similar to Dudgeon Wind Park a solution with several SESs is the most optimal one in terms of cost and regularity. In addition, this study uncovered other very interesting findings when it comes to O&M and marine logistics for offshore wind parks, all of which will be published later this year. The main strength of the developed PhD modelling approach in comparison with other methods is that the flexibility that could be used to introduce and test sudden dynamic changes. Statoil as a future operator of the wind park got an increased understanding of the system behaviour over time, and could look at a detailed level on how work management and marine logistics affected overall performance and system output.

Further work

The simulation model that were used in this decision analysis are currently in the development phase to become a commercial simulation tool for operation and maintenance analysis, and being an important partner in this process is Statoil.

This study was also a part of an on going research project within the research consortium NORCOWE (Norwegian Centre for Offshore Wind Energy) working on identifying how condition based maintenance policies can be implemented to drive down the cost of and increase the performance of maintenance of offshore production assets.