Benefits of collocating vertical-axis and horizontal-axis wind turbines in large wind farms

In this study, we address the benefits of a vertically staggered (VS) wind farm, in which vertical-axis and horizontal-axis wind turbines are collocated in a large wind farm. The case study consists of 20 small vertical-axis turbines added around each large horizontal-axis turbine. Large-eddy simulation is used to compare power extraction and flow properties of the VS wind farm versus a traditional wind farm with only large turbines. The VS wind farm produces up to 32% more power than the traditional one, and the power extracted by the large turbines alone is increased by 10%, caused by faster wake recovery from enhanced turbulence due to the presence of the small turbines. A theoretical analysis based on a top-down model is performed and compared with the large-eddy simulation. The analysis suggests a nonlinear increase of total power extraction with increase of the loading of smaller turbines, with weak sensitivity to various parameters, such as size, and type aspect ratio, and thrust coefficient of the vertical-axis turbines. We conclude that vertical staggering can be an effective way to increase energy production in existing wind farms. Copyright (C) 2016 John Wiley & Sons, Ltd.