The Betz limit applied to Airborne Wind Energy

摘要

In this paper we revisit the modeling framework used to derive the Betz limit of power extraction from the wind based on linear momentum theory. One of our contributions is to suggest that the Betz limit of 16/27 approximate to 59% should in fact hold true for any device that harvests power through drag or torque in a horizontal-axis rotational motion perpendicular to the wind field, which is not only the case of conventional wind turbines but also of Loyd's drag power Airborne Wind Energy (AWE) systems. Another contribution is to show that Loyd's lift power AWE devices during the reel-out phase can harvest up to 4/27 approximate to 15% of usable power available in the wind, i.e. exactly 1/4 of the theoretical limit of the horizontal-axis turbines and AWE drag power systems with ideal airfoils. Moreover, in order to operate at such limit, AWE lift power systems must also extract from the wind an amount of drag power that is equal to the reel-out power. These claims are supported by physical principles and mathematical formulations. (C) 2018 Elsevier Ltd. All rights reserved.