Layout optimisation is essential for improving the overall performance of offshore wind farms. During the past 15 years, the use of yield optimisation algorithms has resulted in a transition from regular to more irregular farm layouts. However, since the layout affects many factors, yield optimisation alone may not maximise the overall performance. In this paper, a comparative case study is presented to quantify the effect of the wind farm layout on the overall performance of offshore wind farms. The case study was performed to investigate two performance indicators: power performance, using yield calculations with windPRO, and wake-induced tower fatigue, using the Frandsen model. It is observed that irregular wind farm layouts have a higher annual energy production compared to regular layouts. Their power production is also more persistent and less sensitive to wind direction, improving predictability and thus the market value of power output. However, one turbine location in the irregular layout has a 24 % higher effective turbulence level, leading to additional tower fatigue. As a result, fatigue-driven tower designs would require increased wall thicknesses, which would result in higher capital costs for all turbine locations. It is demonstrated in this study that layout optimisation using minimum inter-turbine spacing effectively resolves the induced wake issue while maintaining high-yield performance.@en

In this decade, a significant amount of additional wind and solar power will be integrated in the Dutch high voltage grid. The 383 MW nearshore Wind Park Fryslân is foressen to be connected to the Dutch 110kV grid in 2020 through two 55km cable circuits. To quantify the risks of exceeding emission levels for both the TSO and the wind farm developer, harmonic voltage distortion studies must already be performed at an early phase of the project. Relevant data of wind farm components may not yet be available then and must therefore be estimated including data of the wind turbine generator (WTG). The objective of this paper is to assess the impact of a WTG converter impedance model on the harmonic impedance of the windfarm and subsequent harmonic voltage amplification. For this purpose, an analytical converter harmonic model with tunable parameters has been developed. A sensitivity study was performed in a case study of Wind Park Fryslân to analyse the impact of these parameters on the harmonic amplification at the Point of Connection with the 110 kV grid. The length and amount of array cables were also included in the study. The paper follows a step-wise approach where subsequently wind farm impedance, grid impedance and amplification factor have been calculated. It has been found that the WTG converter impedance model has a significant impact on the harmonic amplification of low harmonic orders (h=2 to h=10). Notably, not taking the converter impedance into account (infinite impedance) will result in both over- as well as underestimation of the harmonic amplification over the mentioned frequency range. It is shown that, when no WTG manufacturer has been selected yet, the analytical converter model provides a valid alternative for performing early-stage harmonic studies. @en