Dynamic wind farm layout optimization

To find the optimal spots for movable floating offshore wind turbines through dynamic repositioning

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Recently, there has been an increase in interest in floating wind turbines that are located offshore. These turbines allow for the harvesting of the power of the wind far offshore, where wind speeds are often higher.

Compared to their fixed counterparts, floating wind turbines allow for a certain mobility after the installation. This allows wind farm developers to consider layouts that change throughout the wind farm’s operational phase. The change in layout can increase the energy yield of the wind farm, which may reduce the cost of floating wind energy.

This Master’s Thesis presents a new method for wind farm layout optimization with movable floating offshore wind turbines. The objective function that is maximized is the annual energy production (AEP). The proposed method first finds the optimal installation locations of the turbines, then searches for the optimal wind farm layout for each wind direction while considering the movable range of the turbines. Different movable range sizes are considered in the analysis. These sizes range from small (there is almost no mobility allowed) to large (the turbine is allowed to move anywhere in the wind farm). The results show that the steepest gains are achieved for a movable range size of up to two rotor diameters (i.e., the turbine is allowed to move two rotor diameters in each direction, evaluated from the installation position). Above this range, a large additional movement is required for a minor increase in AEP. Moreover, for this movable range size, repositioning turbines is so effective that their installation positions almost do not affect the AEP.

In addition to the previous method, this Master’s Thesis also presents a novel method to assess the movable range of floating offshore wind turbines. In this method, it is assumed that the mobility is achieved by adjusting the mooring line lengths through a winch system on board of the floater. The proposed method optimizes the line lengths such that an equilibrium is obtained in the relocated position. Various locations are selected for the analysis that cover most of the mooring system footprint on the seabed. The results show that the assumed movable range shape is not the same as the actual movable range shape.
For a 15MW floating offshore reference turbine, the movable range size with the steepest gains in terms of AEP (two rotor diameters) and the actual movable range are compared. The results show that the actual shape covers large parts of the circular shape.

In conclusion, large gains are expected in terms of AEP for movable floating offshore wind turbines. This brings us one step closer to reducing the cost of floating wind energy, which in turn increases its competitiveness with other energy resources.