Land-based supporting structures for wind energy converters

A short state-of-the-art on design verification of supporting structures for wind energy converters is presented. On-going trend in building of land based wind farms is to install larger capacity wind energy convertors at the higher towers. Preliminary studies have indicated that use of higher strength steel (HSS) would be advantages in such applications. However, because of a rather low fatigue detail class of a ring flange connection which is traditionally used for in-situ assembling of segments to a tubular tower, the use of HSS is not justified. That was the main reason to search for an alternative in-situ connections. A possible solution is based on a single overlapping friction connection obtained by preloaded bolts and using open slotted holes. This connection is studied in RFCS research projects, HISTWIN and HISTWIN2, High-strenght tower in steel for wind turbines and Higher steel tubular towers for wind turbines (2012 and 2014), respectively. Parts of these results are presented here. Based on this research a new knowledge is gained to in order to optimize tower design and achieve economic benefits. A case study example of a real tubular tower is used to provide insight in real design values. Other challenges that are associated with the tendency to build towers with higher hub heights are briefly discussed focusing on limits of tubular towers imposed by the traffic constraints. Finally, an outlook for innovation is shown providing an insight into the on-going research projects.