The paper is part of the Grand Challenges Papers for Wind Energy. It provides a status of small wind turbine technology in terms of technical maturity, diffusion, and cost. Then, five grand challenges that are thought to be key to fostering the development of the technology are proposed. To tackle these challenges, a series of unknowns and gaps are first identified and discussed. Improvement areas are highlighted, within which 10 key enabling actions are finally proposed to the wind community.

This study shows the importance of wind turbine blades' wake vorticity, which is ignored in blade-element momentum analysis. We derive a relation between the wake vorticity and blade element drag and demonstrate that the circulation in the wake of a blade element is partly determined by its drag. Also, we find that the airfoil assumption, which is that the elements behave as airfoils, is conservative; the lift:drag ratio of cascade elements is greater than that of the corresponding airfoils.