As wind turbine rotors get larger, the cost and complexity – including the specialized equipment needed to transport longer blades – of wind projects increase. Wind turbine vendors and blade engineers have been interested for years in developing segmented blades that can be shipped in two or more sections. Costs can potentially also be reduced in the blade manufacturing process if two sections require less costly blade moulds, tooling, and other production costs. Substantial progress in this area has occurred in recent years.
Gamesa’s G128 turbine, offered in 4.5 MW and 5 MW configurations, is the first commercial turbine offered with a segmented blade, a patented technology the company calls “Innoblade.” The turbine’s two-piece, 62.5m blade gives the company one of the largest onshore wind turbines, with 128m rotors. The two sections of the blades are joined with nearly 30 metallic bolt channel fittings integrated into the blades. They can be transported on two standard 27m flatbed trailers rather than costlier specialized blade trailers, and they greatly increase the cornering ability of the transport, which is a major challenge with larger blades.
Enercon has also commercialized a segmented blade for its 3 MW E-115 turbine. In this case, the blade is not cut in two horizontally, but lengthwise near the root to reduce the costs of manufacturing the blade. A full length 44m blade of half shells is produced through vacuum-assisted resin transfer infusion. A separate 12m inner section that adds width toward the nacelle and load bearing for the full blade is produced using a separate automated pre-impregnated (pre-preg) fiberglass/resin wrapping process around a cylindrical core that later has its own outer shells added.
Assembly Not Included
Enercon says this hybrid of pre-preg and vacuum infusion with two separate longitudinal sections reduces labor costs and increases the precision bonding needed for the thick inner section. Unlike the E-126 segmented blades that are bolted together during installation, the two sections of the E-115 blades are bolted together at the factory to reduce onsite labor. Enercon’s first commercial use of two-piece longitudinal blades was with its 3.05 MW E-101 turbines, which used a smaller bolt-on section near the root that acted as a spoiler, capturing additional lift. The E-115 blades are an evolution on the earlier E-101 design, as shown in the comparison below.
Enercon Turbine Blades: E-101 and E-115
Other companies with intellectual property (IP) patents pursuing segmented blades include Blade Dynamics, Modular Wind Inc., and GE. Blade Dynamics is furthest along, with its 49m segmented blade that relies heavily on carbon fiber for its internal structures. It is designed to be transported in two pieces that are assembled together on site. It is not yet in commercial use or serial production, but full prototypes were built and certified by DNV GL. California-based Modular Wind Inc. holds patents for a three-piece segmented 45m blade design, but progress is on hold as the company seeks financial backing. GE holds patents on segmented blades, but it has not seriously pursued the technology, instead opting to put effort into its blade extension efforts, which are a form of segmented blade designed as an upgrade.