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Facing up to the ice factor

Climate specific technology and maintenance solutions are being developed to ensuring reliable and efficient productivity in wind rich but icy cold regions

With demand for wind power continuing to grow across the world, more and more wind turbines are being installed in extreme climate conditions, most notably cold climates. However, “wind turbines are usually designed to operate in a temperature range from -10°C to +40°C,” notes GL Renewables Certification. “At some current installations temperatures can drop to -30°C or -40°C.”

This requires turbine manufacturers and project developers/operators to adopt new ways of thinking. “Extreme temperatures present design challenges for turbine control systems”, explains MLS Intelligent Control Dynamics, a full service motion control solutions supplier for community scale and utility scale wind turbines.

“Electronic components, connectors and other delicate components subjected to wide temperature fluctuations can result in the premature failure of these components,” it says.

As a result, it is critical that developers and project owners alike ensure the equipment they specify and the installation, operation and maintenance methods they apply are tailor made to the location of a wind farm.

Cold climate concerns

“A site is considered a cold climate site if minimum temperatures of below -20°C have been observed during long term measurements on an average of more than nine days a year, for a minimum of one hour,” explains GL. “If a site fulfils these conditions then cold climate requirements should be considered in the design of the turbine.”

GL has recently issued an update to its technical note Certification of Wind Turbines for Extreme Temperatures. This provides information on load assumptions, safety and control systems, manuals, rotor blades, nacelle covers and spinners, machinery components, strength verification, building structures, and electrical installations.

“In very low temperatures applications, steel, plastics and even the wiring used in subsystem fabrications need to be designed to withstand cold climates,” says MLS. Its engineers work with the manufacturer's turbine designs, adapting control system features that are designed for arctic climates.

The firm’s low temperature packages include internal heaters, cold-weather lubricants, heated sensors and appropriate alloys for structural element. “To make turbine operation possible at lower temperatures, specific turbine components are sealed and cold-weather tolerant batteries and capacitors are integrated into our pitch systems,” it adds.

All of these component elements should be routinely checked as part of a good ongoing proactive maintenance schedule.

Leading turbine manufacturers are already forging ahead. Repower, for example, recently completed the delivery of 12 of its Cold Climate Version (CCV) MM92 turbines to Golden Valley Electric Association (GVEA) for its Eva Creek Wind Project. The 24.6MW project is set to become the largest wind project in Alaska to date, with commissioning planned for next year.

With a hub height of 78.5 metres, REpower’s 2.05MW CCV unit is “specifically designed for the harsh Alaskan climate,” says the company.

“Our Cold Climate Version of the successful two-megawatt-series has been designed for sites with heavy temperature fluctuations and humid weather, and has already proven itself in projects in Québec, Canada and in Inner Mongolia, China,” says Repower’s Chief Executive Officer, Andreas Nauen. “This project demonstrates Repower’s core competency in supplying extreme cold climate capable turbine technology.”

Indeed, the company has similar deals for the CCV machine lined up in Canada, including a recent supply agreement for 25 units in 2013 for five projects being developed by WindWorks Power Corporation in Ontario.

The ice factor

Combating potential ice build up is a key need for cold climate turbines. With temperatures in Canada typically falling below -20°C, Repower’s CCV features additional heating units that keep the wind power plant operational even at -30°C “thus delivering constantly high yields”.

Moreover, as Antti Laakso, Marketing Director for Finnish wind turbine manufacturer, WinWind notes:

“In cold climate areas, ice formation on rotors is a risk.” A recent report by WSP Environmental on behalf of Nordic Energy Research, entitled Wind Power in cold climate, agrees.

“The general effects of icing are increased vertical loads on the structures as well as increased wind drag due to the larger area exposed to the wind,” the report says. However, it concludes that the industry is still lacking suitable and much needed ice detectors for direct measurements of icing, stressing there are “no verified and fully reliable” detectors available.

“In order to enable forecasts and investment decisions on prevention systems reliable ice measurements (synoptic measurements) in the planning stage is needed,” it says. In addition, “Development of di- and/or anti-icing systems is needed.” These should, preferably, be installed at the pre-construction stage.

WinWind is investing EUR 8m to develop a new, arctic 3 MW wind turbine and hopes to be able to come up with solid solutions to the icing issue. In addition to the Arctic region, there is market for arctic wind turbines in the mountainous areas of Central Europe too, notes the company.

“In the cold climate areas of the North, wind power is utilized very little compared to its rich potential,” says Jarkko Väinämö, the responsible director of the development project at WinWind. “Also, for all practical purposes, the standardisation work of the cold climate area wind turbines is only starting.”

He also points out: “We can now fully utilize the experience we’ve got from the Uljabuouda wind park, which we delivered to Swedish Lapland”.

As well as using specially designed components, most cold climate turbines on the market have a safety feature that automatically shuts the turbine off when too much ice has built up on the blades. In addition, some feature special coatings to combat potential ice effects.

The fibreglass reinforced blades on Northern Power’s 100 Arctic wind turbine, for example, “come with a specially formulated hydro phobic polymer coating ensuring a smooth surface so ice cannot easily build up on the blades”. If ice does form, “the black blades absorb the sun’s heat and allow for ice to be shed easily”.

Significantly the unit adopts gearless technology. “Our Permanent Magnet Direct Drive technology and simple design architecture are why the NPS 100 Arctic requires only minimal preventative maintenance,” it says, suggesting maintenance checks only need to be conducted once a year.

“In this way you can set your maintenance schedule to avoid particularly harsh seasons. Additionally, the gearless technology bypasses much of the long-term maintenance issues that are associated with the more conventionally designed gearbox turbines.”

Low temperature castings, meanwhile, ensure safe operation of the NPS 100 Arctic turbine to -40° C, while the power converter and controls cabinet are heated to maximize operation, expanding possible operating temperatures. Air density compensation enables maximum energy capture in cold environments, while the tubular tower and enclosed heated nacelle means maintenance and service personnel are protected from uncomfortable and often dangerous conditions.

The other extreme

But as Repower points out, to meet today’s growing global demand, wind turbines also need to be able to operate efficiently and withstand extreme heat as well as cold.

“As wind blows everywhere, Repower has developed special wind turbines that deliver maximum performance even in the extreme climates of Australia, Canada and parts of the United States,” it says. “In particular, the converter of a wind power plant should be safe from overheating. Merely dissipating its heat is not a sufficient solution to this. The component must be actively cooled down.”

MLS agrees. “Additional thermal management considerations come into play in very high temperatures,” it says. “Depending on the turbine's operational environment, electronic components that otherwise become too hot during operation will require cooling systems.”

Repower has designed a hot climate version of its turbine, equipped with additional breather assemblies to ensure optimal wind turbine performance up to 40°C.