Offshore Renewable Energy: The Critical Role of Metocean Data in Offshore Environments

Robin Stephens, Metocean Group Manager, BMT ARGOSS

The weather presents a number of major risks to an offshore wind farm development at all stages throughout its life cycle. Detailed understanding of site-specific meteorological conditions is therefore essential for effective risk mitigation.

Robin Stephens, Metocean Group Manager at BMT ARGOSS, a subsidiary of BMT Group Ltd, the leading international maritime design, environmental and engineering consultancy, outlines the risks and opportunities and explains the importance of robust Metocean data.

While the socio-politically driven desire for renewable energy continues to gather pace, economic factors are still amongst the primary drivers influencing offshore wind farm developers. Accurate wind resource assessment is fundamental for confirming economic viability of a wind farm, and accurate, long-term Metocean data is essential for feasibility appraisal, design, construction, operation and maintenance. The inter-annual variability in wind conditions also needs to be factored into contingencies and insurance. For safe and cost-effective planning it is essential to know when is the best time to carry out specific weather-dependent operations, and also to quantify the expected weather downtime. For complex, multi-stage offshore operations, it is appropriate to undertake 'workability' simulations based on long-term Metocean time series data. Metocean data is, therefore, fundamentally important to wind farm developers.

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The renewables industry is still relatively young and somewhat fragmented in its approach to through-life project support. Arguably this is a function of the fact that at different stages in the design, installation and operation of a wind farm, different organisations are involved; there are different requirements and different technologies. However, a holistic approach to weather risk understanding through the whole life cycle of the development, from initial feasibility and economic viability assessment, through detailed structure and mechanical design, planning for and executing the installation and then during operation and maintenance will pay dividends. To gather in-situ Metocean data, an obvious solution is to deploy a weather mast, which on the face of it is a very valid, very competent strategy. However a weather mast is extremely expensive and will only provide data for the period post-installation. Furthermore a single weather mast will only provide data for a localised area which will not necessarily be representative of the entire area of wind farm development which maybe larger than the size of the Isle of Wight. Innovative solutions are required for complex problems.

Metocean1Understanding the extreme environmental loadings expected over the life of a project is essential for defining the structural and mechanical design, reassuring investors and obtaining certification and insurance. For aspects of structural design and performance assessment, it is necessary to look to historical Metocean data, to understand about the variability in weather patterns and extreme conditions in determining the survivability of any structure we place out into the ocean. The UK Round Three Licensing moves renewables out into much more hostile waters than have been worked in so far. It is important to learn the lessons of the offshore oil and gas industry when considering structural and mechanical engineering design, safe installation and survivability in the most onerous environmental conditions that can be reasonably anticipated. It is also important to address the structural response of a turbine foundation to severe wave loadings. Data indicates that wave loadings on a turbine base would, under certain conditions, be similar to those experienced by slender offshore oil and gas structures where high frequency wave loadings can cause unexpected structural responses. These issues must be recognised and addressed in offshore wind farm developments too.

Meteorological and oceanographic forecasting services are also required to manage the day to day operations of installation and maintenance and also to predict energy yield. With the present wind farm infrastructure, there's a relatively low sea state tolerance for safe access to turbines and this profoundly limits the windows of operation for maintenance. With access to long term historic information about weather variability, for installation and maintenance, operators can identify likely favourable windows for safe working and can also estimate the amount of down time which we would anticipate in having people and vessels in the field that cannot actually work because the limiting weather conditions are being exceeded. Effective planning based on best available information is both a health and safety and economic advantage. Wind farm operators also have an economic interest in quantifying and forecasting the wind conditions for their site, so that yields can be accurately estimated. This is vitally important to ensure that the operator maximises its revenues while avoiding being penalised by the Transmission System Operator (TSO) for missing its obligations.

The offshore oil and gas industry has been coping with offshore weather risk for well in excess of 40 years now, so there is a great maturity of understanding in how to address many of the issues that now face offshore wind farm developers. The offshore oil and gas industry has also learnt the benefits of undertaking meteorological and oceanographical studies for a very early stage and then progressively building on this knowledge through the evolution of development, so that each component of the project is approached with an element of continuity. There is also awareness that during initial feasibility assessment, it is very easy to produce preliminary environmental estimates based on limited information, which may prove subsequently to be significantly in error. In the case of offshore renewables, if those preliminary estimates are too high, then that may impact economic feasibility assessment adversely. Conversely, if the preliminary estimates are way too low, a preliminary design may be conceived which in the event does not work because it needs to be engineered more substantially than those preliminary numbers would indicate.

The lessons learnt by the offshore oil and gas industry are that undertaking very competent Metocean work at an early stage in the process is very beneficial to reducing initial commercial and engineering uncertainty. As the project evolves, more Metocean work is done as the design is advanced to ensure that outstanding uncertainties in the preliminary estimates are progressively reduced.

One area where the maturity of the oil and gas industry has borne fruit is the progressive recognition of the benefits of cooperation. In key oil and gas basins throughout the world, there is often a significant joint industry approach to understanding meteorological and oceanographic conditions. Such a collaborative approach would be hugely valuable to the renewables industry. It is worth recognising that for the oil and gas industry, the environment is a collective problem, while for the renewables industry, there are elements of both risk and reward. While there will be sensitivities between the different operators, in terms of understanding the environmental yields in different locations there are benefits from collective regional approaches, sharing data, sharing, modelling expertise and costs. It would be crazy if every new renewables field development feels the necessity to reinvent the wheel rather than sharing data and adopting industry standard best practice.

Another valuable legacy from the offshore oil and gas industry is the extensive use of in-field measurements of winds and waves which, in the North Sea, goes back to the mid-1960s. Access to certain long term measured data sets, has given BMT ARGOSS the opportunity to improve and validate its skills in numerical modelling. It is now possible to construct very reliable and accurate fine scale numerical models which can help maximise the efficiency and cost effectiveness of monitoring systems in the field. Advances in meteorological modelling have enabled BMT ARGOSS to estimate wind conditions at very fine scales down to around ½ kilometre spatial resolution. This is extremely important in the context of wind farm developments where a large number of turbines are placed close together. Using a combination of in-situ measurements, advanced high resolution numerical modelling and satellite remote sensing, there are now many advanced capabilities that can be brought to bear on the challenges facing the renewables industry. So both building on the heritage and understanding of the offshore oil and gas industry and embracing more recent technology, there is a lot that BMT ARGOSS can offer to provide invaluable, cost effective support to this new industry.

To manage the multiple weather related risks faced by offshore wind farm developers and operators, an integrated approach to wind resource assessment, Metocean data provision, environmental model hindcasting, workability analysis, extreme value analysis and forecasting is required to gain high quality information across the large sea areas now being developed.  Furthermore, such an integrated approach ensures consistency and cost-effectiveness. BMT ARGOSS recently launched its dedicated 24/7, 365 days a year operational, maritime weather forecasting service. Utilising advanced in-house operational, numerical modelling at global, regional and local scales, together with satellite observations and in-situ real-time measurements, BMT ARGOSS' forecasting services can be tailored for the offshore renewables industry. With access to such advanced support, the opportunity for wind farm developers to mitigate against weather risk and take benefit from weather opportunities has never been greater.

This article was first featured in Society of Maritime Industries. To read similar features, visit their website.

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Contact Information

Robin Stephens

First Floor, 3700 Parkway,
Solent Business Park, Whiteley
Fareham, Hampshire
PO15 7AL
United Kingdom

Tel: +44 (0)1489 889260

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