Tower - Innovative Outcomes

Direction and Rate of Technological Change

Structural reliability is key to the design of a turbine tower. The tower must be built so it can handle the heavy static loads applied due to direct wind pressure and turbine weight. In addition, the tower design is optimized by considering the energy yield gain and costs. Tower height has increased over time, motivated by rotor blade diameter increases over the past two decades. As the tower height increases, wind turbines have access to a steadier wind speed profile at higher altitudes and generate high power output for a given turbine rating and rotor diameter. In the current market, the tubular steel tower is the most prominent design because of its high strength-to-weight ratio and comparatively low cost.

However, the growing demand for taller towers has posed several transportation challenges, including requiring large cranes for installation, increasing site development costs, and potentially longer lead times. Therefore, concrete-made towers have emerged as an alternative to tubular steel towers, with the comparative advantages of potential cost savings in transportation and site development, no local buckling problems, and greater corrosion resistance. Another design alternative, hybrid steel-concrete towers, combines the advantage of tubular steel sections on top and a concrete base on the bottom. This hybrid design reduces the challenges of transporting large diameter steel-tubes and makes the tower’s overall seismic weight lower than concrete towers.

Figure IO.1 Trends in Turbine Hub Height and Rotor Diameter
Source: Recreated from Figure 20 of Wiser et al. (2017) 2017 Wind Technologies Market Report. U.S. Department of Energy, Office of Energy Efficiency & Renewable Energy.

Overall, research and development in the tower industry have been focusing on building taller wind turbine to unlock more wind energy at a lower cost, and at the same time identifying ways to overcome logistics challenges through shipping towers in smaller components and/or completing most installation on-site. GE Renewable Energy introduced a new logistics-friendly space frame wind turbine tower which can be easily transported via standard shipping containers and assembled at the job site. The space frame wind turbine tower is equipped with a specialized lift which provides easy access for future maintenance. Vestas also launched an innovative large diameter steel tower that enables to achieve cost reduction through increasing the strength of the tower base while using little extra steel. To solve the transportation challenge posed by the wider tower, the bottom tower section is delivered in three lengthwise segments and assembled on site.

Data on Quantity, Cost, and Quality

Table IO.1 Attributes for Learning Curve Estimation
Source: Data from Figures 12 and 20 in U.S. Department of Energy 2017 Wind Technologies Market Report

Year	Tower Production Capacity (number of towers)	Average Hub Height (meters)
1998-99		56
2000-01		58
2002-03		66
2004-05		74
2006		76
2007		78
2008		78
2009		79
2010		80
2011		81
2012	3,823	84
2013	4,285	80
2014	3,714	83
2015	3,119	82
2016	3,150	83
2017	3,220	86
Source:	Figure 12	Figure 20

Figure IO.2 Manufacturing Production Capacity for Major Components of Towers, Blades and Nacelle
Source: Figure 84 from AWEA 2017 U.S. Wind Industry Annual Market Report Year