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Canada

Canada

Cold comfort for wind power developers

An icy climate can have a major impact on the performance and economics of a wind power project, even in areas with favourable wind conditions. Diane Bailey reports on how Canadian researchers are working to enable the industry to overcome the problem.

Ice can cause a project to lose up to 10% of production
Ice can cause a project to lose up to 10% of production
The extreme cold and ice that is a feature of northern climates presents unique challenges to wind farm development and operation in Canada.

While turbine technology allows machines to survive temperature dips down to bone-chilling levels, there is still a lot of work to do to minimise the impact of cold-climate issues on the economics of a project.

"When you are talking about cold climate you are really talking about two different sets of issues," says Frédéric Côté, general manager of the TechnoCentre Éolien, which operates a research facility on Quebec’s Gaspé Peninsula.

"The first is related to temperature and the second is related to icing. So far, what we see is that the cold temperature issue is quite under control."

The operational limit of a standard wind turbine is –20°C, but most manufacturers have cold climate adaptations of their technology with low-temperature steels, synthetic lubricants and heating systems in the nacelle, alongside other critical components.

This allows turbines to operate at temperatures as low as –30°C and remain structurally sound even at –40°C.

"This is sufficient for most cold regions," agrees Dr Christian Masson, a professor at the École de Technologie Supérieure in Montreal.

Ice issues

One problem for which the industry is still searching for solutions, however, is that of icing. "It is a major, major issue," says Côté. "Icing affects all aspects of a project."

Even during the wind resource assessment phase, the freezing of anemometers and weather vanes can result in lost or erroneous data, making it hard to produce a good evaluation of the resource, Côté says.

In extreme cases, ice accumulation has even caused the total or partial collapse of an entire meteorological tower.

Once a wind farm is actually in operation, icing can affect the aerodynamic profile of the blades. It can be responsible for mechanical problems from increased vibration and greater component fatigue caused by an imbalance in the ice load.

And the risk of ice fall can prevent access to the turbine, delaying maintenance and repair. "It translates into an increase in cost," says Masson.

Studies suggest that wind farms can suffer a 5-10% loss in production because of ice, although Masson says that quantifying the impact can be difficult because icing tends to be a local phenomenon that varies widely from site to site.

Another complication is that identifying when production losses can be fully blamed on icing is a challenge in itself.

Ice sensors used by the industry are not completely reliable and it is not always possible for researchers to go to see the ice for themselves.

"Some numbers have been published, but they vary from one region to another and also from one way of evaluating the losses to another," Masson says.

Côté cites an example of a Quebec wind farm that was shut down for two weeks last winter because of an icing event.

In a country where wind energy output is at its highest during the coldest months of the year, he says, anything that affects turbine operation can be pretty problematic, from an economic perspective.

"You have the most wind during the winter, so you need your production during this period," says Côté.

Various strategies are being employed to deal with the issue, including heating blades and measurement instruments, painting blades black in an effort to use solar radiation to warm them and prevent ice accumulation, and applying low adhesion coatings to make it harder for water and ice to stick.

Côté believes that, so far, nobody has found the right recipe. "To be honest," he says, "most of the technological solutions for the icing problem are still under development."

Combined effort

Some of that development is taking place under the auspices of Canada’s Wind Energy Strategic Network (Wesnet).

This brings together 39 researchers from 16 universities to work with industry and grid operators, and is midway through a five-year, C$6.5 million (£3.9 million) research programme that is delving into a variety of technical challenges confronting the Canadian wind sector.

Wesnet has a number of cold-climate projects under way, says Masson. Researchers at Quebec’s Laval University, for example, have developed a prototype for an ice-free anemometer that require less energy to heat than those currently in use.

"When you do a wind assessment, typically, you don’t have easy access to energy, so you have to reduce the consumption of the equipment you install on the towers," explains Masson.

"You need an intelligent system that will tell you if you have to heat it or not."

Problems with meteorological towers collapsing because of ice build-up have led researchers at the University of Manitoba to develop a prototype tower made of advanced composite materials, which is undergoing testing in the field.

In addition, scientists at the University of Quebec at Chicoutimi working on anti-icing and de-icing methods for blades have completed wind-tunnel testing on a heating system that is strategically located on the blade to prevent ice accumulation.

The next step is to evaluate its effectiveness on a full-sized installation in the field.

Predicting ice build-up

Wesnet’s work also goes beyond technical adaptations designed to mitigate icing. Masson is team leader for a cluster of projects aimed at improving wind energy extraction in cold climates through better understanding of the impact of ice and cold on the behaviour of turbines, the assessment of wind energy potential and the prediction of a project’s energy output.

One area of study involves the creation of a model to predict the accretion of ice on turbine blades, says Masson.

Another group of researchers is working on methods to forecast icing events, which go hand-in-hand with the wind forecasts that have become an important tool for utilities trying to deal with increasing amounts of wind energy on their systems.

"The grid operator wants know what the wind production will be and, in cold climates, you also have to predict whether there will be icing events," says Masson.

"You could have very good wind but if the icing is strong, you might decide not to operate the installation."

Mapping out where and how icing is likely to occur is also important, says Côté. "Not all icing is the same — you have frosty snow, you have hard ice, you have all kinds of problems you can encounter," he explains.

"We are working with meteorological data to try to see which places are most likely to get icing events, what kind of icing you can get there, and the impact it could have on production."

Worthwhile research

Finding ways to improve the performance and economics of wind projects in harsh climates is a challenge, but the payoff can be significant.

At a 2008 European conference on wind energy in low temperature and icing conditions, German turbine maker Repower estimated that China’s then-target of 30GW of wind by 2020 would require 70% of the capacity to be built at cold-climate sites.

The European Wind Initiative, which sets out research-and-development strategy for the next ten years, identifies turbine optimisation for complex terrain and cold climates as a short-term priority.

Masson expects the tools and technologies being developed in Canada to be applied at sites in Asia, Europe and the US.

"This work could be used where you have similar conditions," he says. "Cold weather is cold weather."   

RESEARCH IN ACTION HOW THE INDUSTRY IS IMPROVING ITS RESPONSE TO THE COLD

Two Repower 2.05MW turbines that came online at the rugged and hilly tip of Quebec’s Gaspé Peninsula in March provide a natural laboratory to test the impact of Canada’s sometimes harsh climactic conditions on wind installations.

"It’s a good site if you are looking for trouble," says Frédéric Côté, general manager of TechnoCentre Éolien, which owns the turbines.

"The setting of our installation is unique. We are really talking about cold weather and complex terrain. And we are near the Gulf of St Lawrence, so we are near salty water as well. It’s really a nice setting if you want to investigate those kind of conditions."

The humid winds blowing in off the Gulf contribute to what Côté calls very good icing events at the facility, the Site Nordique Expérimental en Éolien CORUS (SNEEC).

Such events are one of the reasons why German wind turbine manufacturer Repower is closely monitoring the performance of the machines before installing a further 477 turbines in the province at wind farms under contract to Hydro-Québec.

Although the turbines at SNEEC are already a special cold-climate version of Repower’s MM92 model, the company is working with the TechnoCentre to make sure they operate effectively in the ice and snow of a Canadian winter.

Plans for the site go well beyond validating the technology of one turbine manufacturer, however. The turbines are available to universities, colleges and companies that want to use them in their own research or to evaluate pre-commercial products and services.

"We are working with a couple of companies to test some new devices by installing them on the turbines and seeing how they operate in cold climates," says Côté.

Backbone

Providing the infrastructure that scientists and the wind energy industry needs to further their understanding of cold-climate issues and develop solutions is a key part of the TechnoCentre’s mandate.

In 2007, it opened a research facility in Murdochville, Quebec, drawn by the cold north-west winds that sweep through the Gaspésie at an average speed of nine minutes per second.

An important piece of research infrastructure there, says Côté, is an innovative multi-measurement tower equipped with anemometers, wind vanes and instruments to measure temperature, relative humidity, barometric pressure and ice, as well as an array of data acquisition systems.

The installation is used not only to identify conditions that cause ice formation, but also to assess the performance and reliability of measurement instruments under harsh conditions.

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