6.1. Proposed Layout
The proposed Layout is shown in Drawing 1. The area of the wind farm is 21.5 km². The prevailing wind direction is 220° and the wind farm orientation (the turbine rows) is perpendicular to that direction. The distance between the rows along the wind direction is set to 1400 m (≈9D) and the distance from turbine to turbine in the crosswind direction is 950 m (≈6D). This results to a loss of production due to wake of approximately 5-10% (John Andrews, 2007)
Using Jansen’s model, we further calculated the losses at 6%. The calculations are included in the appendix.
Since the longitudinal direction of the wind farm is almost parallel to the seabed contours, the bathymetry is uniform. The mean depth is 22 m with deviation from the mean of less than ±1.
6.2 Grid connection and cables
The selected transmission technology is bi-polar HVDC. The transmission loss using HVDC are assumed to be 3%. The investment cost for HVDC system is much higher than for HVAC but HVAC has larger transmission losses. Thus, in the long run HVDC in a better choice. The voltage level for the wind farm internal network will be 36 kV. The 36 kV AC of the wind farm internal network will be converted into a high-voltage direct current. The sea cable will be a bi-polar DC cable, transporting the energy to the point of common coupling, where the DC voltage is again converted to high-voltage alternating current.
Each of the turbines in the offshore wind farm will be equipped with an individual transformer, to transform the low voltage of the wind turbine generator into the 36 kV voltage of the wind farm internal network.
The total length of the infield cables is 17.84 km. The cable will be buried in the seabed at a depth of 1.5 m.