Nonetheless, it was NedWind which earlier this year took delivery of the last of eight huge blades from Rotorline, each of which was hoisted onto an enormous trailer and transported to the site of Windpark Moerdijk. Here NedWind is erecting four 1 MW turbines. Each blade is 25.15 metres long -- not the longest in the world, but according to Rotorline director Jaap Olthoff, probably the largest blade manufactured in series production.
Olthoff joined the company in 1991, not long after Rotorline had become part of the NedWind family after NedWind's takeover of bankrupt Bouma. It soon became clear that the blade production facility was under utilised. "We could produce one 20 metre blade a day, but Nedwind was certainly not selling a turbine every two or three days," explains Olthoff. "Two years ago we started trying to sell our blades to other customers."
These early attempts proved fruitless. To start with, NedWind Heerhugowaard only produced blades that fitted NedWind turbines. On top of that other companies were reluctant to buy blades from a company they regarded as a competitor. So during 1994 the ties between the two companies were loosened, both technically and financially. "We changed our product portfolio. We now make a series of blades that is comparable with, let's say, LM," says Olthoff, referring to Danish blade manufacturer LM Glasfiber. The decision to sell blades for installation on a variety of machines meant the development of a new mounting system. Rotorline developed a system for connecting the blades in which the bolts are embedded in a V-shaped plastic matrix. This matrix fits into the edge of the blade root, forming a permanent link.
No such link existed between NedWind Heerhugowaard and NedWind, though both were daughters of Hollandse Industriele Maatschappij (HIM), formerly Hollandia Kloos. Olthoff points out that the majority of shares in Rotorline are owned privately, including by members of the company's management. Rotorline today employs 50 people. The turnover in 1995 was NLG 8.5 million -- a bit less than expected, according Olthoff. "The market for wind turbines in the 250-350 kW size range was disappointing," he adds.
For the near future, he is reasonably optimistic. While reluctant to identify the company's six new customers, Olthoff names DeWind of Germany and Ishikawajima-Harima Heavy Industries of Japan. The others include one Spanish company, two from Denmark and one of the biggest turbine producers in India.
Blades at Rotorline are still made of glass reinforced polyester with no epoxy content. According to Olthoff, use of epoxy makes no difference in fatigue behaviour of the blade, but is a dangerous substance to work with. "We make our own moulds from epoxy. I think half of the people that work in production now show an allergic reaction to it."
Production at Rotorline has been partially automated. One of the features is the automated lay-up of impregnated glass fibre matting, described by the firm as an oriented fleece. Manual labour is still necessary for working with the lay-up from that point. Blades are cured at a temperature of 70 degrees Celsius to promote proper meshing with the plastic matrix.
Rotorline blades, which are for use on stall and pitch controlled rotors, are computer-designed and blade geometry is formulated in tandem with the Netherland's national laboratory, ECN, using profiles from the Institute of Wind Energy at the Technical University of Delft. Standard Delft profiles are used for the outboard blade sections, while a modified "thick blade" profile makes up the inboard end, keeping lift to drag ratio to a minimum. A third member of the blade design team is Stork Product Engineering in Amsterdam.
Both Rotorline and Stork are involved in the development of the Nedflex, a pitch-controlled variable speed rotor now being tested on the test bed once used for the Flexhat research and development programme between Aerpac and ECN. "Only now it is not really a flexible blade anymore. It didn't give the advantage we expected. So we are working on a blade which is connected to the hub with a hinge," says Olthoff.