It is well known that the efficiencies of turbines in a wind farm can be significantly lower than that of a single turbine on its own. While small wind farms can achieve a power density of over 10 W/m2, this can drop to a little as 1 W/m2 in very large installations The first law of thermodynamics dictates that turbines must reduce the energy of the wind that has passed through them. However, turbines also inject turbulence into the flow, which can make it more difficult for downstream turbines to extract energy.
“For large wind farms, there is a limit on how much energy can be replenished on the order of 1 W/m2,” says Antonini. “[The turbines] create a kind of uniform wake across the wind farm.” The wakes of these large farms could extend tens of kilometres downstream, potentially affecting other wind farms.
Perhaps AWES could experience this problem less as they would have to work at different heights.