The retrofit covers all blades installed, under installation or dispatched, says Kher, irrespective of geography. "Most of the blades of that particular version exist in the US," he adds. "Our investigations thus far do not suggest any manufacturing defect irrespective of where they have been produced."
For the North American market, the company's blades are made at a facility in Pipestone, Minnesota, that opened in November 2006. America is the largest market for Suzlon's 2.1 MW machines. Last year, it delivered 795.9 MW of the model globally, with America taking the lion's share at 462 MW. The balance went to Australia, Portugal, and Brazil. Of those delivered last year, 333.9 MW were commissioned in the US, with 27.3 MW commissioned in Australia and 39.9 MW in Portugal.
Kher says Suzlon has studied the pattern of damage to the blades and determined that a combination of various stresses arising due to dynamic load conditions, predominantly shear stresses, has given rise to cracks in one particular location on the outer shell of the blade. The occurrence of these cracks is in a localised area of the blade structure, pointing to the need for strengthening that particular area.
The repair work is simple and effective, says Kher. The localised area of weakness will see the application of an additional layer of laminating fibre glass material to reduce stress levels at that location.
The company says a total of 930 of the total 1251 blades to be replaced are already installed on turbines. For the replacements, Suzlon is dispatching an improved version from its factories in India, China and the US. Turbines will not sit idle for the entire time their blades are being repaired. "In order to minimize the downtime of turbines due to the retrofit program, we are introducing a rolling stock of about twenty rotor blade sets to be used as temporary replacement of blades sent for retrofit," says Kher.
It is still a big job. "From what I've heard, all the blades will have to hit the ground, and that's a lot of crane-work," says Chris Bley with Rope Partner, which often helps with such work. The current boom in wind turbine installation means that cranes of the right type and size are in short supply. "It's a big crunch on the crane side for sure and there are probably a lot of companies taking advantage of that situation." Suzlon's Kher, however, says the company has not faced any difficulty procuring cranes and other assets for the job and does not expect any.
Blades continue to be among the more problematic components for wear and tear, says Bley. Last year, Gamesa had problems with its first blades made in America (Windpower Monthly, May 2007) and repaired and replaced some. More recently, Clipper Windpower began a blade retrofit program on 260 rotors (Windpower Monthly, February 2008).
In general, Bley feels that not enough field-testing of blades is being performed. "From my sense and from being in the industry long enough, I believe they are putting them out to market too quickly. You really need to sit on these things and watch them for a period of time, but it's the nature of the business right now."
Suzlon's Kher says all Suzlon products are brought to the market through well-established processes, including initial designs being certified by independent agencies such as Germanischer Lloyd, a testing program with technical university TU Delft in The Netherlands, and "rigorous" in-house and third-party quality assurance checks at each stage of the manufacturing process.