Knowledge Development for the Design of Offshore Wind Energy Technology


change requires extensive academic and industrial research and the amount of possible design changes is enormous.


There is great support for the presumption that there is potential for major change in this industry. However, in practice there are limited conceptual changes that prove this. The results of desktop designs and failed developments indicate that expectations may need some tempering. Extrapolations of experience curves lead to predictions of 25–40% cost reductions by 2020, but these studies use expert opinions that may be influenced by just these expectations. Furthermore, historical data for offshore wind farms that can be extrapolated from are limited. Such plants may not be good indicators of the potential for the large technological changes that are suggested.


How Convincing are Desktop Design Studies? Most desktop design studies base their conclusions on preliminary design results, using many assumptions and simplifications. When a preliminary design is made there may be a small overestimation in cost because the design has not yet been fully optimised. Many uncertainties will result in underestimation. Simplifications are not normally compensated for by larger safety factors, although the complications that are ignored will generally lead to higher costs when detailed design solutions are generated. The comparison of such preliminary designs with more detailed designs or actual systems is tricky, because it will generally result in overoptimistic conclusions.


When the dimensions of a single fixed concept are varied, the effect of simplifications will be correlated. This makes simplification suitable for parametric optimisation or trend studies. However, in studies that compare different concepts, some of the assumptions will not be correlated. As a consequence, the uncertainty is often larger than the difference between the concepts. For example, in a study of monopile support structures a pile without scour, protection was found to be cheaper than with protection, but under equally likely assumptions of armour rock and steel costs the conclusion was reversed. The rewards presented in much research appear to be either too small or too uncertain to match the risk of large technological change.


Many studies only address a part of the system, so it is not always clear whether a comparison is actually fair. Some concepts appear to be interchangeable, but may actually perform slightly different functions. For instance, a stall-controlled rotor cannot directly replace a pitch-controlled rotor because the latter also has a function in meeting grid requirements. Different concepts of components may also have different secondary effects on the rest of the system or on manufacturing, installation or maintenance procedures. The consistency of a comparison of concepts is not always maintained, not least because the effects on a system level are not generally an explicit target of the studies.


System Design and Integration


The enormous number of alternative technical concepts for offshore wind energy calls for a process that is highly effective in terms of the time needed to find better solutions. Case studies of sub-systems such as support structures have provided knowledge about the methods used to analyse their behaviour as well as information on properties exemplifying design solutions. These studies generally do not provide information about the effect of the integration of such solutions in a wind farm. The value of the design solutions at a system level is left


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uncertain, therefore much additional work is needed to determine whether the results of these studies can positively affect the development of offshore wind energy.


For the synthesis of system architecture, the pre-selection of concepts is generally based on qualitative information and expert judgement. Due to the concepts of interest being relatively extraordinary, the available knowledge on which to make these design decisions is limited.


When considering design integration, it is misleading to think of offshore wind energy as a regular design problem. The long-term development is an autonomous process in which many asynchronous design activities are undertaken that are inter-related through market mechanisms. One might argue that with vertical integration of the supply chain and the emergence of companies that do both project development and manufacturing, the interactions between the design processes become closer. However, it is not obvious, that the synchronisation of design activities provides the best solution. An example of this is rotor-nacelle assemblies, which are designed and made for many wind farms to benefit from the reduced costs and risks associated with large production volumes. The support structures for these assemblies are normally site-specific to benefit from tailoring to local conditions. Therefore, all-encompassing integration of offshore wind farm design is perhaps not the target.


Focus Research on Design Methodologies Many research activities contribute to the knowledge needed to perform simulation and analysis in the form of models and computational tools. Most design-related studies and practical experiences contribute to knowledge about the suitability and properties of certain design solutions.


Research on methodologies is limited and focused on optimisation. This is a pity, because methodologies lend themselves well to transfer from academia to industry and have the potential to improve the effectiveness of designs in industry. Designers are an enormous resource here.


There are high expectations of system integration and conceptual variation, but both are ‘methodologically challenged’. Conceptual variation is currently based to a large extent on qualitative reasoning, intuition and possibly even wishful thinking, lacking profound quantitative information. Integration is complicated by the many asynchronous design processes at different companies, with interaction through market mechanisms.


Previous research activities have introduced integration into the picture by enrolling designers in an integrated design project outside their individual companies. However, this has failed to bring integration into the companies.


New research should aim to support integration of in-house design processes in the industry. This would benefit from the availability of quantitative information that can be generated quickly for different conditions. Previous studies have resulted in engineering models that provide such information and the applied principles could be further exploited and made suitable for integration support. Only when such methodologies acknowledge asynchrony in the design processes can the full capabilities of industry designers be employed in the quest for better technologies for offshore wind energy. n


MODERN ENERGY REVIEW – VOLUME 2 ISSUE 2


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