Set against the great advantages of offshore wind energy - its higher energy capacity and reduced visual and acoustic impacts - is the higher cost of the energy. It is thus imperative that research address how costs may be reduced, and how falls seen in solar and onshore wind costs in recent years may be replicated. Unfortunately, all features of the resource availability, collection and transmission, up to the point of grid connection, must be well defined in order to evaluate the cost of energy. A range of disciplines in natural sciences and engineering is thus inevitably involved (as well as in micro-finance and economics). Study of existing commercial offshore wind farms is, furthermore, of limited utility, as alternative layouts cannot be explored, and data on power production (or even the wind resource) are typically confidential, making it difficult for researchers in different fields and institutions to work together on common datasets.

These challenge may be addressed through the definition of a fictitious - but commercially plausible - reference wind farm (RWF), with the methodologies and findings developed being applicable over a common class of wind farms. The NORCOWE offshore RWF is situated at the FINO 3 met mast, some eighty kilometres west of the island of Sylt in Schleswig-Holstein, Germany, near the Danish-German border. (A real wind farm, DanTysk, has recently been built in the vicinity.) It comprises a set of eighty wind turbines of (fictitious) 10 MW DTU reference type, and a grid connection involving two substations and two HVAC links to shore. Mean water depth at the site is 23 m, and the substrate is sand with some gravel and silt constituents. Turbine foundations are monopiles.

The mast was installed in 2009, so met-ocean measurements are available over a number of years with which to validate and calibrate model climatologies. Adoption of the 10 MW reference wind turbine ensures researchers have access to a complete aerodynamic specification, and should maximise the uptake of our results and findings in the design of the next generation of offshore wind farms. Information on the variation of mean water depth and substrate in the vicinity of FINO 3 is purposefully ignored in the layout design: such variation can, in the real world, end up dominating the design, but this then leads to methodologies and findings without a generalised applicability.

Two contrasting layouts and associated operational regimes have instead been defined from the wind climatology in a baseline exercise, using ground rules developed in consultation with industry. The exercise did not include an optimisation effort; rather, the aim was to provide a starting point usefully close to an optimal solution, and thence to stimulate further work on possible layouts and operational regimes.

One of the layouts is somewhat novel, with turbines being located along curvilinear rows and a bounding perimeter, the shape of the latter reflecting the directionality of the wind resource. Spacings between turbines on the perimeter are smaller, in keeping with state-of-the-art industrial practice. A second, more conventional layout involves turbines located on a rectilinear grid, with rows lying normally to the direction from which most wind energy is available, and turbines aligned across rows. Both layouts occupy the same area of seabed.

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