As the number of sites with high wind speeds for turbines becomes exhausted, there is a growing need to ensure that sites developed in the future make optimal use of the wind resources available. Also, as wind turbines are deployed in remote, forested areas of Northern European countries, such as Sweden, Finland, and Germany, the larger wind shear and turbulence created by forested terrain favors larger towers that elevate the rotor.
This trend places greater emphasis on using towers with heights often in excess of 100 meters and capable of supporting the heavier top head mass of large, multi-megawatt turbines. This is the motivation behind the new breed of hybrid steel and concrete towers, where the bulkiest concrete base section can be produced at a factory and shipped in more manageable sections or produced at the wind plant site. Some specialized towers, available only recently, can reach as high as 150 meters.
By Land or Sea
A primary reason for the increasing demand for these hybrid towers is transport logistics. With steel towers, erected tower height directly dictates the maximum diameter of the tower’s lowest base section because all wind towers gradually taper as they rise. The typical tall tower height today for onshore turbines is 100 meters, and the base dimensions for these towers are typically not more than 4.3 meters in diameter. Widths any larger are not only difficult and expensive to manufacture (because of the challenges of bending thick steel plate), but they also push the boundaries of the cranes and specialized transport vehicles needed to move them. Likewise, these oversize loads are more limited as to the roads, intersections, bridges, underpasses, and wind plant sites they can travel through.
Hybrid and concrete towers can also offer a more cost-effective solution when the nearest steel tower facility is far from a given wind plant site, which would require prohibitively costly transport for steel sections. Some wind turbine vendors that have experience working with steel, concrete, and hybrid towers will select their tower type based on these relative materials economics. If a steel tower facility is in reasonable proximity to a planned wind plant, steel will be chosen. But as the distance and transportation costs from a steel tower facility increases, shifting to a hybrid or all-concrete offering can be more cost-effective, since concrete facilities are more widespread.
New Form Factors
A number of European companies, including Max Bögl, Advanced Tower Systems, Ventur Droessler, Inneo Torres, and Consolis Hormifuste, are now offering hybrid and concrete towers. Max Bögl appears to be the current market leader in Europe, with units installed with turbines from Senvion, Vestas, Nordex, Alstom, and Gamesa. Wind turbine vendors Acciona and Enercon also produce concrete and/or concrete and steel hybrid towers for self-supply.
In more expansive markets, such as North America and China, greater land availability reduces the premium on maximum tower height. But at least three companies offer concrete or hybrid towers: Postensa in Mexico and Fabcon and Tindall in the United States. Tindall offers 40-meter concrete base sections that can be used in conjunction with another manufacturer’s steel towers. And the European vendors with a proven track record could expand to the United States and elsewhere globally.
Other approaches to tall towers, such as General Electric’s space frame lattice tower and Siemens’ bolted steel shell tower, offer different approaches to building tall towers and alleviating transport headaches. These and hybrid concrete towers are likely to begin to be installed in the United States in the next few years as the market continues to mature.