This is a multidisciplinary project that brings together researchers from different academic backgrounds in order to address reliability, lifetime and efficiency in offshore wind farms, and to meet the needs of the UK electricity generation industry. The overarching aim is the reduction of the (levelised) cost of generation of the large offshore wind farms that the UK will need in order to meet national and international objectives in the reduction of CO2 emissions. The multidisciplinary aspect reflects the different but, in context, linked disciplines and brings together the growing discipline of energy meteorology, of aerodynamics and aeroelasticity, of fatigue and structural mechanics, and of systems control. That is, the approach is a holistic one, linking the environmental conditions with their impact on each rotor and the mechanisms to improve farm performance as a whole.

The meteorological contribution is essential because of the range of wind flow conditions that exist, subjecting the turbines and - importantly for large wind farms - the wakes of the turbines to a range of unsteady conditions that are known to reduce wind farm efficiency, and to cause increased structural damage (when compared to small-scale onshore wind farms). Both these contribute to increased capital and operating costs. The energy potential for the UK from offshore wind is huge, but offshore wind energy is still at a relatively early stage in technological terms.

The aerodynamic response of each turbine to a variety of conditions imposed by the wind flow and the wakes of upstream turbines depends on the aeroelastic behaviour of the blades, the load in turn imposed upon the turbine generator, and the response by the turbine control system. In a large wind farm, the behaviour of one turbine - principally how much energy it is extracting from the wind flow - affects the behaviour, efficiency and lifetime of wind turbines in its wake; the turbines are not independent of each other. In fact, all aspects of the performance of wind turbines within large offshore wind farms, whether power output, loads or operations, are affected by their interaction through the wakes. Hence, to improve the cost effectiveness of offshore wind energy requires a better understanding of the flow-field through the wind farm. The project will address this issue and develop models to better represent the flow-field including the wakes and turbulence. Furthermore, capitalising on this, the implication for loads on the individual wind turbines will be investigated and the design of control strategies will be explored that achieve optimal operation of a large wind farm with each turbine controlled to keep operations and maintenance costs to acceptably low levels whilst (subject to this constraint) maximising farm output.

Potential Impact:
This project is about improving the efficiency and reliability of wind farms for national electricity generation, in particular the large offshore farms that the UK will need so as to reduce its dependency on fossil fuels. There are two aspects to this reduction. One is simply replacing fossil-fuel plant. The other is with how energy is used, more broadly, in the future. Reduction in demand through, for example, improved housing insulation will likely be more than offset by increased demand. A major increase will come from all-electric vehicles replacing conventional personal and public transport, the latter primarily coming from buses and rail electrification.

The research itself will be beneficial to wind farm developers and operators in achieving best economic performance. These assessments come from the developers and operators themselves, but crucially they also come from independent specialist consultancy companies providing software tools and due-diligence services. For a new wind farm these services - whether from the developer or independent assessor - need to provide accurate assessment of wind resource, how best to use this resource in terms of turbine size, control system type, number and layout of turbines, grid connection requirements etc., and how best to operate the turbines in order to keep maintenance costs acceptably low while obtaining output as high as possible in terms of power supplied to the grid at any one time and the overall energy generated, thereby maximizing return on investment. While tools and knowledge exist to a high level in UK, the knowledge gained from relatively new large (non-UK) offshore wind farms has shown substantial shortcomings in both understanding and capability of the tools. Offshore wind energy is still at a relatively early stage in technological terms.

The present proposal addresses wind resource, loads on turbines, in particular fatigue loads, and operating the turbines in an optimal manner so as to keep operations and maintenance cost as low as possible and the energy yield as high as possible, so that the life-time operation is optimized. One of the crucial issues in large farms comes from the wakes of turbines impinging on downwind turbines, but it is not economic to place the turbines far apart. Therefore, the wind farm has to be designed and operated so as to make the adverse consequences acceptably small. Existing wake modelling is known to be seriously deficient. In addition, existing tools do not adequately take into account the types of wind flow that in fact exists most of the time (of stable and convective wind flow). With the replacement of large conventional plant with offshore farms it is highly desirable that wind farms should be able to operate much as conventional plant. The fact that the wind resource is variable makes this not necessarily fully achievable. But, operating the turbines individually - subject to demand from the grid on the one hand and the impinging wind flow conditions on the other - in an overall supervisory control framework, will provide a better strategy than is available at present. This last, is an integrating aspect of this proposal.

The move towards substantial increase in offshore wind power will give the UK a leading role internationally in the design and operation of wind farms at a high technical skill level. Increased UK capability will make the UK a better-informed buyer for its own national needs as well as raising its own export-earnings market for low CO2 energy economies. Greater knowledge and improved capability of modelling tools will improve the economics of large offshore wind power through reducing the uncertainties in design and operation, and will assist policy makers. Increased use of wind power will also reduce dependency on imported (fossil-based) fuels, and the associated uncertainties in the global context in which those fuels are obtained.