We have written recently about the cost and logistics problems in transporting towers and blades for wind turbine projects on US highways and by rail. The cost as we indicated is typically between 10 and 25% of the project cost because the component parts of the 80 mtr (260′) towers are pushing the limits of what is possible to move by road and rail, requiring special permits and transportation equipment. Turbine efficiency and power output however are reliant on wind speed. So what is the industry to do if the average wind speed increases 8% between 80 and 100 mtrs, if many of the best sites for 80 meter towers are taken and if generators are demanding 3 MW where previously 2 MW was sufficient? Higher power outputs require not just stronger wind speeds but larger blade diameters increasing the load on towers bearing the turbine and blades.
To produce 100 mtr (330′) towers requires by definition stronger towers, traditionally this has been done by thickening the steel used in the wall of the tower. At 14.5′ diameter existing 80mtr towers are at the limits of what can be moved by road even when the tower is broken down into three sections. But a US manufacturer North Star Wind Towers of Nebraska appears to have hit on a solution. The lowest tower section (by definition the widest diameter in any tapering design) is made in sections and assembled on site. The result is thinner wall sections, larger base diameter allowing shallower foundations, higher load limits and 10-15% lower total tower cost. The panels can be mixed to provide varying tower dimensions allowing standardized factory production ” meaning better tolerances and lower mass production costs and are bolted on site allowing an 85-90% reduction in welding.
Whether this will prove to be the mainstream design for the next generation of wind turbines remains to be seen but certainly a solution needs to be found to the problems of transportation and rising costs if wind power is to meet the aspirations of its supporters and more importantly financiers in the years to come.