Servicing of wind turbines is now big business around the world and is growing with every new machine that goes into operation. Each turbine with a traditional gearbox drive-train technology is a potential candidate for major gearbox overhaul several years down the line.
Larger independent firms are entering the repair and refurbishment market to compete with original manufacturers, so there was little surprise when global automobile component firm ZF Friedrichshafen, which had recently entered the turbine gearbox sector, made a major investment in repair and test facilities. But while the growing demand for turbine gearbox repairs should accommodate new players, some gearbox manufacturers themselves question whether the independents can provide the service required.
An estimated 90% of turbine owners take the refurbishment option, with the same warranty and expected lifetime available on a refurbish as a new gearbox. As a rough guide, the cost of three standard refurbishments is equal to that of a new gearbox.
Opinions differ over gearbox resilience. "It is now accepted that a turbine can't be run for 20 years without wear and tear and the need for maintenance and repairs," says Soren Klyvo, CEO of Mekanord, a Danish firm that refurbishes wind-turbine gearboxes. "In general, a turbine will have to be equipped with a refurbished gearbox two to three times in its 20-year lifetime. Alternatively, it will receive a completely new gearbox at about the same cost. This is the broad assumption made in financing wind projects," he says.
"A wind-turbine gearbox generally has to be refurbished after eight or nine years of operation, depending on whether the winds at the location are turbulent or steady," says Gert Korbijn, wind energy sales manager at Stork Gears & Services, an independent international gearbox repair and service firm, which refurbishes 100-150 turbine gearbox a year.
"Some gearboxes don't last more than five to seven years before a refurbishment is needed. It is unusual for a gearbox to run for more than ten years without a refurbishment," argues Marcel Pooth, manager at ZF Services in Dortmund — part of ZF Friedrichshafen — which currently carries out around 100 wind-turbine gearboxe refurbishments a year.
Nevzat Oezcan, vice-president of service at Siemens-owned wind-turbine gearbox manufacturer Winergy, is more circumspect. "It isn't possible to generalise about when gearbox faults are likely to arise. There are various factors at work and if a turbine is used at a location with wind characteristics for which it was not designed, problems are more likely to occur," he says. "Even though the reliability of gearboxes has significantly improved in recent years, there is a growing need for gearbox repairs simply because the wind-turbine fleet is getting larger," he adds. Winergy does not reveal the extent of its refurbishment activities.
It is clear that the need for refurbishment is increasing with the annual increase in geared turbine installations — dampened only by the recently growing popularity of direct-drive wind turbines without gearboxes. However, Danish wind-industry research firm BTM Consult estimates that more than 32GW of last year's 39.4GW of new global wind capacity came from geared turbines.
In 2005, around 10GW of wind turbines with gearboxes were commissioned around the world and in 2006 the figure was almost 13GW. Within the next couple of years, these machines may well need substantial attention. This translates into a possible 5,000 gearbox overhauls next year, rising to 6,000 in 2013. Looking further ahead, around 32GW of geared turbines were commissioned globally in 2010, resulting in another 16,000 gearboxes needing refurbishment by 2017-20.
In Europe alone in the same period, 7GW of turbines with gearboxes were installed, which will need 3,500 refurbishments. Yet each of the small number of prominent European companies that provide high-quality full refurbishment has or will have, at most, the capacity to do about 200 gearboxes per year. So considerable expansion of facilities will be needed.
Companies carrying out gearbox repair and refurbishment generally fall into four different types of business. First are the small workshops, which tend to repair gearboxes from older, smaller and locally based turbines. Secondly, there are medium-sized independent companies — such as Danish marine-gearbox specialist Mekanord — which carry out fuller refurbishments.
Mekanord has until now handled around 30 gearbox refurbishments a year. However, seeing the potential for growth, the company has launched a strategic initiative to refurbish up to 200 gearboxes a year within the next few years and is now serving the whole European market due to relatively low transport costs.
Gearbox manufacturers such as Winergy and Moventas constitute the third type of company to carry out repairs and refurbishments. Many stepped up activities when the economic crisis that began in 2008 led to a sharp fall in demand for new turbines and thus for gearboxes.
Stronger and larger independent companies, including ZF Services and Stork Gears & Services, are the fourth company type. Some of these are posing a challenge to gearbox manufacturers in the refurbishment market. "The independents are generally more flexible and have faster response times," says ZF's Pooth, adding that the gearbox manufacturers, driven by growth targets, have had to put servicing to one side to focus on series production of gearboxes.
But whether independent companies can and should get into the business is a moot point with gearbox manufacturers. "A third party cannot check that the repair is carried out according to the original specification because they do not have the original specification and design data," says Oezcan of Siemens-owned Winenergy. "Nor can the third party build in all gearbox upgrades such as improved reliability and safety facilities that the original manufacturer provides."
Product liability is also an issue, he adds. Most gearbox manufacturers provide repair services, but only of their own gearboxes on grounds of product liability. "There can be legal consequences if a gearbox from another manufacturer is repaired and it then fails," he explains. He is also sceptical as to whether third parties could ensure compliance with the European Machinery Directive — EU legislation that makes manufacturers responsibile for ensuring certain health-and-safety standards are met — when they don't have the original specifications and design data. "If the operator decides in favour of a third-party repair, he should be aware that he takes the risk of product liability issues under the European Machinery Directive," Oezcan says.
But Stork's Korbijn disagrees: "When we repair a gearbox, all the reusable components are inspected thoroughly and, as our parts are of at least the same quality as the original equipment manufacturer's, we provide a full warranty on the gearbox. We initially cannot take responsibility for the design, however, unless we receive an order to fully recalculate the design," he says, adding that he does not know of the EU Machinery Directive having any influence on the refurbishment of gearboxes at Stork.
Korbijn adds that his company can also build individual custom-made new gearboxes for turbines, something that gearbox manufacturers with production-line activities may be less efficient at doing.
ZF Services will soon be competing in the manufacturer's market as well as repair and refurbishment. It opened a new repair and test shop in Dortmund, Germany, in June to expand from around 100 refurbishments per year — focused mainly on Vestas, GE and Nordex turbines — to up to 200 per year from 2012. "ZF Services can overhaul gearboxes produced by Winergy, Bosch Rexroth, Hansen, Moventas, Jahnel-Kestermann and others," according to Pooth.
In parallel, the company is starting its own turbine gearbox manufacture. From 2012, it will supply 2MW gearboxes exclusively to Vestas that it says will perform for 20 years without replacement, from a factory under construction in the US state of Georgia. It is also manoeuvering to take control of turbine gearbox manufacturer Hansen, initially securing a combined 38% from Indian company Suzlon and UK investment company Ecofin in late July.
Pooth believes that over the next decade gearbox repairs and refurbishment will become the domain of the gearbox manufacturers and larger independent companies. Smaller companies may lose their clientele as the more mature markets such as Germany, Spain and Denmark repower wind farms and eliminate machines under 1MW. On top of that, turbine operators will change, with smaller operators becoming rare as energy utilities, investment funds and banks move in. Operating larger fleets, they will tend to choose larger firms in the turbine and component repair sector, he says.
Ultimately, costs will bear in. The price for a new gearbox for a 2MW turbine can hover between €160,000-190,000. A gearbox with a standard refurbish — in which bearings are replaced, the gear teeth overhauled and reground and the components measured — costs from €90,000 to over €100,000. The logistics, crane and manpower for removing or replacing a defective 2MW gearbox can cost €20,000-40,000 if the whole operation takes place within one day — up to double that if it is removed, repaired and replaced at a later date. If damage such as a broken shaft has to be rectified, the cost can rise up to €130,000. A damaged gearbox may be feasible to repair up to a cost of €150,000-160,000. Beyond that, turbine owners usually decide go for a new one.
FROM TURBINE REMOVAL TO TESTING — THE GEARBOX REPAIR PROCESS
When gearbox problems arise that cannot be resolved in the turbine itself, the first step is to remove the gearbox from the turbine, which is usually done by a local operations-and-maintenance company or by the original equipment manufacture, explains Gert Korbijn, sales manager for wind energy at Stork Gears & Services. Once out of the turbine, the gearbox is loaded on to a trailer and transported to the repair centre.
Up to three years ago, it was common for operators to wait for their own gearbox to be repaired as the lead time for delivery of a new one was one to two years. But since the economic crisis reduced demand for new gearboxes — causing prices to fall — and to reduce turbine downtime, gearbox refurbishers hold exchange gearboxes in stock, which are sent immediately for installation so a turbine stoppage may last just a week. Korbijn says his firm has replacement gearboxes in the range 500kW to 2MW.
After the faulty gearbox arrives at the workshop, it is dismantled. The components are cleaned and undergo a technical examination. An inspection report is then drawn up, which is checked by quality control and sent with a repair proposal and quotation to the customer. Depending on the size of a gearbox, an inspection takes one to two weeks. If no damage exists and only the bearings are replaced, the gearbox can be ready to use again after another three to four weeks.
If repairs are necessary and replacement components have to be made, this process may require up to five weeks. Reassembly takes another week or two.
A gearbox requiring substantial repairs may thus spend eight to nine weeks at the workshop. The refurbished gearbox can then be tested at the workshop, says Korbjin, or it can be tested under load conditions at a test bench at one of the company's suppliers.