An Improved Determination of the Tower Height That Maximises the Power Output per Unit Cost of a Small Wind Turbine

Abstract

This Note considers the determination of the optimum tower height, defined as the height that maximises the ratio of average power output to the total capital cost of the turbine and the tower. A previous analysis, Wood (2001), gave the optimum height when the power output increases monotonically as the wind speed increases, that is without any consideration for the rated operation or the necessity of shutting down the turbine to avoid excessive loads at high wind speeds. This deficiency is rectified by assuming that the actual power curve consists of a region where the power increases as some power of the wind speed, followed by a region of constant power, after which the turbine shuts down. Because increasing tower height is associated with increasing wind speed, this change considerably reduces the optimum tower height. Using data from a commercial manufacturer, it is shown that the optimum tower height can be considerably less that the maximum tower height offered for sale. The optimum height is shown to increase with increasing surface roughness.