Wind turbines with taller towers and larger rotors designed for efficient power generation in areas of low-speed wind have taken over the industry over the past few years with no sign of slowing. At this year’s HUSUM Wind 2015 wind conference and exhibition in Germany, four new low wind speed models were unveiled to the market by four top wind turbine original equipment manufacturers (OEMs). These turbines are targeted toward the Northern European wind market where low wind speeds and space constraints favor these designs, but they are growing more popular. The system specs show the industry is continuing to innovate and push the boundaries for onshore wind turbines.
Denmark’s Vestas unveiled the largest rotor variant of its 3 MW platform—its new V136-3.45 designed for low wind International Electrotechnical Commission (IEC) class IIIA sites. Following now-typical naming conventions in the industry, the 136 denotes rotor diameter in meters, and the 3.45 represents the turbine’s rated megawatt capacity. The 66.7 m blades are Vestas’ largest yet for onshore turbines, and are the latest in a series of blades released in recent years that follow the company’s switch to structural shell designs after decades of using a central spar design. As with long blades from other vendors, preimpregnated carbon fiber plays a key role in achieving strength and length with manageable weight. The blades also have a slim design that is augmented with aerofoils, vortex generators, and serrated trailing edges (which appears to be a newly revoked patent previously owned by Siemens).
Also notable is the use of the Vestas’ large diameter steel tower (LDST), a tower design that is detailed in Navigant Research’s Supply Chain Assessment 2014 – Wind Energy report. Put simply, the tower design vertically splits the largest bottom tower section into three shell sections that are bolted together at the wind plant site. This allows for a wide enough base (6.5 m) to support hub heights of 132 m and 149 m.
Germany’s Senvion also unveiled a new IEC IIIA low wind turbine, the 3.4M140, which features a 140 m rotor using 68 m carbon-infused blades and hub heights of 110 m and 130 m. This is an uprated design from the company’s current 3.2 MW, 122 m rotor offering. Notably, the doubly fed induction generation drivetrain moves to full power conversion on the new model from partial conversion on the existing 3.2 MW units. Senvion achieves its tall hub heights using a hybrid approach that combines lower sections of prestressed concrete with standard tubular upper sections. Navigant Research has detailed recent hybrid tower designs, which are the most common approach used to reach high hub heights.
Uprating the drivetrain is German company Nordex’s approach to its new low wind turbine, the N131-3.3MW. This turbine retains the existing 131 m rotor and carbon-infused 65.5 m blades used on the company’s current N131-3.0 offering, but uprates the power output with changes in gearbox torque, generator, and power converter (retaining DFIG with partial conversion). The N131-3.3MW is also designed for remarkably tall hub heights of 134 m and 164 m by use of hybrid concrete and steel towers.
European OEMs weren’t the only players showcasing new low wind offerings at HUSUM. U.S.-based General Electric (GE)—which has grown minor market share in Germany—unveiled a 3.2 MW turbine with a 130 m rotor turbine designed for IEC IIIA wind speeds. GE’s largest offering presently in the low wind category is its 2.75-120 model, so this is a notable uptick that brings the company closer in line with its European competitors. Hub heights for the 3.2 MW turbine will range from 85 m to 155 m, with the higher-end options employing GE’s unique space frame design, which features a bolted lattice tower covered in fabric.