Comparative life cycle assessment of tubular wind towers and foundations - Part 1: Structural design

The use of tubular towers made of steel, concrete or hybrid steel–concrete has become standard in the wind energy industry. However, more powerful wind energy generators are leading to the need for increasing the towers height. This implies rethinking of existing solutions for the support onshore structure composed of tower and foundation, including design concept, life cycle and environmental repercussion. The need for transportation of larger prefabricated elements and more complex processes of assembling on site become important issues. This paper addresses the comparative study concerning the influence of increasing height on the structural design and outcome of different structural solutions. Steel, concrete and hybrid steel–concrete wind towers with heights of 80, 100 and 150 m supporting multi-megawatt turbines of 2, 3.6 and 5 MW power respectively are addressed. The design of the towers is made in accordance with the structural Eurocodes. Two different scenarios are addressed, the first considering common lifetime of 20 years and the second considering increased lifetime of 40 years with reuse of tower parts. In-situ erection of steel tubular parts is achieved using flange connections or newly developed friction connections. Conclusions point out that, for towers up to 80 m, the use of steel tubular sections and flange connections are the most suitable. Friction connections are suitable for higher towers, leading to less material consumption. The use of concrete towers, particularly for heights above 100 m, is penalized when seismic risk is considered in special in the dimensions of the slab foundations