Tildy Bayar, Associate Editor, Renewable Energy World
June 11, 2013 | 4 Comments
LONDON -- Nacelle access solutions such as ladders and climb-assist technologies have been in place since there have been wind turbines, but as turbines get taller, service lifts (SLs) are becoming the solution of choice for new-built towers.
To some extent the SL market competes with climb-assist technologies, but needs differ depending on tower height. In Europe, climb-assist or ladders are normally used in towers up to 60 metres, while in towers above 60-80 metres there will typically be a lift. In North America and Asia lifts are less common, but still a growing market.
"Most of our customers see a very good business case in having a lift in a high tower," says Erik Laursen, CEO of Avanti Wind Systems. Lifts improve safety and productivity. Taking tools, spare parts or material such as, say, 20 litres of oil up to the nacelle can be a time-consuming and exhausting job using ladders; a lift enables more service visits per team per day and reduces stress on workers.
"Imagine climbing a vertical ladder that's 262 feet (80 metres) high, just to start your job," said a statement from the US-based Basin Electric Power Collective (BEPC) explaining why it installed SLs in its 188 wind turbines in 2012. "It is physically very demanding to climb the ladder, even with climb-assist," says Laursen. Lifts enable companies to retain experienced technicians whose ladder-climbing days may be behind them.
Differences and Advantages
The cable-guided (wire rope) SL system uses a traction hoist and is guided with cables on either side, which keep it from rotating but allow it to move as the tower flexes with the wind. "There's a lot of sway," says Bill McBrayer, North America access manager at Tractel, "so the lift has to be able to move a bit." The ladder-guided system is guided by a ladder anchored to the tower, while in the rack-and-pinion system the lift rides along the ladder; the rack is on the ladder with two motors on the lift and a pinion driving the lift up and down.
The wire rope system is less expensive because it uses fewer components. It is the market leader for this reason, says McBrayer, while the ladder-guided system is more stable. The rack-and-pinion system is the most expensive and is less commonly used.
"All are good solutions, but we view the wire-guided as a very good lift: simpler and most cost-effective," says Laursen. But, depending on the configuration of the tower internals, there are advantages to the other solutions too. The ladder-guided lift can save space in the tower, since lift and ladder are combined into a single system. But Laursen points out that ladder-guided lifts must have doors at the top and bottom in case of the need for emergency egress. In the wire-guided lift a worker can simply step out of the front door and over to the ladder, with no need to crawl through the lift.
Technicians interviewed said there are "no issues at this point" with SL safety. In fact, in our conversations with people who work on and around wind turbines, it emerged that not one had ever seen, or even heard about, a lift-related accident. One technician had seen "a few heart attacks, but you can put that down to an unhealthy lifestyle rather than the lift".
Andre De Meirichy, engineering manager at PowerClimber Wind, identifies contact between moving lifts and people working inside the tower as a potential hazard. Other principal risks include falling from the lift, being hit by falling objects and electrical/mechanical hazards. Trade body RenewableUK says that while lifts can address many of the health and safety issues involved in wind turbine development and maintenance, their installation could also lead to other risks such as fire and compromised emergency rescue.
The only problem technicians reported with SLs is occasional overloading after attempts to carry too much equipment up to the nacelle. "The person driving has to be mindful of how much load [the SL] can take," said one technician. "Two big German guys plus their work gear might overload it," he joked. "But overloading is driver error, not technology error."
There is currently no global standard covering SLs; standards differ between countries and regions. European SLs are covered by a Machinery Directive (in place since 2009) rather than by standards that apply to elevators, since elevators are passenger-operated while SLs require a trained operator. There are no issues with the European standard, says Laursen; "We are quite happy with the standard and it gives a good foundation for us."
In North America, however, standards are problematic and differ by state and region. Each Canadian province and U.S. state has its own regulations for SLs. For example, Quebec and Texas have no regulations – in Quebec this is because wind turbine towers are not defined as buildings – while Ontario and California feature some of the most stringent.
A U.S. national standard is in the works, spearheaded by AWEA, but there is indecision regarding whether SLs should be classed as elevators; if so, increased regulation would be required. According to McBrayer, climb-assist technologies are currently selling more widely in the U.S. because of the SL standards issue, and the uncertainty is driving a need for further cost reductions. "On one hand," he says, "we're being asked by the [OEMs] to lower costs. At the same time [the industry is] writing a code that's adding more cost to be compliant." If the new standard is driven by the elevator sector, he says, unnecessary costs will be added: "Gates at the bottom; protection in case someone would be underneath when [the SL] comes down, which would probably never happen; limit switches on landings. If [the standard is] driven by elevator safety concerns, which we've had zero incidents with, we're in conflict," he says.
"We make the same lift as our competitors – they are compatible (the dimensions are about the same). And connection-wise, electrically they are about the same," says De Meirichy. This compatibility is important when selling to multiple OEMs.
"From the outside you could say [our SLs and our competitors'] look more or less similar," says Laursen. For him, product differentiation lies in experience, installed base and market strategy. "For the past four to five years we have developed not only individual products but the complete package," he says, "basically everything inside a tower: the ladder system with fall protection equipment, SLs, platforms, railings, lighting systems, cable trace, electrical components, control panel."
Most SL companies also manufacture other nacelle access solutions: ladders and climb-assist technologies. For example, Hailo's core business is ladders and they have branched out into making SLs.
Offshore and Older Turbines
SLs for offshore turbines are basically the same design as onshore, but somewhat larger, according to Laursen. Lifts in multi-MW turbines typically have the capacity to carry more people and bigger loads, so they can bring up heavier components. In addition, says De Meirichy, specifications are tougher offshore because SLs must have more robust anti-corrosion qualities.
In older towers which may only have a ladder installed, De Meirichy says, it is easier to retrofit a climb-assist than a lift. The key issue is dimensions, and space can be a problem. Increasingly, he says, the decision to install a lift is taken when turbines are replaced.
Business Is Looking Up
Laursen sees the SL market as a growing one. Market drivers include ever-increasing turbine heights and growing awareness of health and safety issues in emerging markets. Although there are no compiled statistics on SL penetration, Laursen says, "We can look at our customers and how many SLs they are using in their products and ask, do we see an increase – and yes, year-on-year, we see an increase."
Lead image: Lifts enable more service visits per team per day, and reduce stress on workers. Courtesy Avanti Wind Systems
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