How blockage effects can raise wind farm power production in yield assessment

Analytical wake and blockage models are essential tools for wind energy layout optimisation and energy yield assessment because they provide a necessary balance between computational cost and predictive accuracy. While blockage is often viewed as a simple loss factor that reduces total wind farm power production by a few percent, it primarily functions by redistributing momentum. It is shown analytically that including blockage can in fact raise total power production with respect to a wakes-only only approach, particularly when turbines operate near or above rated wind speeds. PyWake simulations confirm that this mechanism can also be found in wind farm yield assessment as long as blockage-related speed-up effects are included and should not be interpreted as an error in the coupling between wake and blockage effects. The analytical derivation also highlights that blockage and wake losses need to be adjusted if blockage is applied as a simple knock-down factor to wakes-only yield estimates to ensure zero bias with respect to fully coupled approaches.