Presentations

Abstract

Offshore wind farm development in the North Sea continues to lead the industry, with countries such as the UK, Belgium, and the Netherlands having significant projects already in commercial operation, whilst opening large areas of their respective ocean space for the development of future projects. With limited space and more aggressive, national electrification targets however, the industry may need to design denser wind farms going forward. Such is the case for the newest development area to be auctioned in Belgium this year, with a target capacity of up to 3.5 GW in an area of 260 km2, surrounded by many existing and planned wind farms within 80km. The result is a development zone with a density of approximately 14 MW/km2 in a region of active operation and development which will be subject to large wake effects. The authors note that Belgium's wind projects historically have high power densities [1]#_ftn1, which are regulated by law due to the limited size of the country's offshore area. However, this does provide an interesting case study for wakes. Industry accepted engineering wake models have been developed and validated against historic offshore wind farms, comprising of smaller turbines and installed capacities than current projects. Present and future turbine models now extend further into the atmospheric boundary layer, with some tip heights reaching above 300m. As such, engineering wake models may not be sufficiently capturing the wake effects for such large turbines. In recent years, weather-based models of different fidelities have emerged and may be more appropriate to capture the effect of atmospheric physics on wake effects in wind farms with such large turbines. Accurate energy yield assessments are the cornerstone to ensuring both feasible and bankable wind farm projects. Yet different wake models, and their implementation, can lead to a range of results that can impact project viability. Hence this work presents a comparative study of multiple industry accepted models versus weather-based simulations and the resulting differences between them considering such a dense cluster scenario and region. The authors have derived indicative layouts for the Belgian zone and have modelled relevant neighbouring wind farms. A comparison of the internal and external wake impacts estimated by the engineering and weather-based models considered has been undertaken. The results revealed general alignment in the external wakes predicted, contrary to expectations given the high development activity. Interestingly, the comparison showed a larger deviation for the internal wake impacts under tight spacing restrictions between engineering and weather-based wake models by as much as 10 % or more. A sensitivity analysis has been undertaken to investigate the drivers behind the extent of alignment or misalignment of different models. This work will provide insightful results for development considerations of offshore wind farms under high densities and with large turbines. It can further serve to encourage industry collaboration in reaching an improved understanding of wake effects under such design conditions and highlighting new modeling techniques. #_ftnref1[1] Baltic LINes, Deutsche WindGuard GmbH, "Capacity Densities of European Offshore Wind Farms," 2018.