The Rapid Evolution of Wind Turbine Tower Structural Systems: A Historical and Technical Overview

Utility-scale wind farm development has been underway in the US for approximately three decades, and in that time, the tower structural systems (for supporting large wind turbines) have changed dramatically—from relatively short 20 m to 40 m steel lattice towers and guyed or self-supporting poles; to moderately tall 40 m to 60 m thin-shell steel fabricated tubes; and to the current wind industry standard of taller 80 m to 100 m steel fabricated tubes. Moreover, the observed evolution stages in wind tower design seem to have occurred approximately every ten years. So as the US wind industry enters its fourth decade, it is not surprising that wind tower design appears to be at a new threshold. Recently, the wind industry's attention has turned to a new generation of very tall 100 m to 160 m concept and prototype tower structural systems that include: flexible steel fabricated tube "soft" towers; multi-petal steel towers; hybrid towers constructed of both steel and concrete; all-concrete towers of post-tensioned concrete construction, either cast-in-place or precast; and next generation steel lattice towers, i.e., "space frame" systems. This paper provides a historical overview of these changing wind tower designs and describes the pertinent technical aspects of their structural engineering. The paper then explains the tower changes by discussing their underlying causes and effects. It discusses the changing design conditions in the wind industry that have been and are continuing to drive and shape the rapid evolution of wind turbine tower support structures.