Wind turbines aren’t yet as reliable or cost effective as the industry would like them to be. What’s more, most turbines are so new, their maintenance costs are an unknown figure. According to research from UK-based Wind Energy Update, 79% of today’s fleet are still under manufacturer warranty. This is about to change.
The huge building boom we saw from 2005 to 2009 launched many new turbines into the field. These units have relatively low maintenance costs, regardless of who’s footing the bill, and relatively high availability. However, look at the lifecycle for a turbine and see operations and maintenance costs for wind power are typically double or triple projected costs. To correct this oversight manufacturers have begun offering extended service warranties as long as 10 years.
“There isn’t one silver-bullet strategy,” says enXco’s Dave Luck. “Because of the diversity of owners and developers, along with the trend that more and more of the assets are utility owned, an extended warranty may not be the best strategy.” Project owners range from community-owned one-offs to Fortune 100-owned, power market focused projects. As such, each owner requires different services from the manufacturer. “If a small or medium-sized owner is relying on bank financing, they are certainly choosing the 10-year warranty option because it limits the conversations with the bank regarding risk” explains Luck. At the other end of the spectrum, a large-scale project owner such as NextEra Energy or MidAmerican Energy Holdings is better off sourcing its own maintenance contracts. This is where independent service providers really add value to a project.
Beyond the who-pays-for-what predicament that is so prevalent in the wind industry, predictive and preventative processes have become more common over the last couple of years. Predictive maintenance solutions such as condition monitoring can provide a substantial boost to turbine availability.
Condition monitoring is a way to keep tabs on power-production equipment that is often on wind farms in remote locations and then mounted on 60 to 100 m towers. They are not the easiest power plants to check. Condition monitoring equipment assists with vibration sensors on main bearings, gearboxes, and generators, sending vibration signals to a monitoring station. Thanks to the internet, this station could be miles away and the monitors there responsible for several wind farms. The vibration signals alone reveal little, but after they trend for a few months, it’s possible to tell where trouble is brewing.
Analysis software called Fast-Fourier Transforms can associate a frequency with a vibration so it’s possible to nearly pinpoint an ailing component. Knowing the general speed of a component, say a 300-rpm bearing in the second stage of the gearbox, it’s possible to spot its vibration amplitudes. Since bearing generally do not fail catastrophically, the vibration amplitude can be tracked as it rises and the bearing scheduled for replacement at the O&M crew’s “convenience” and not as a surprise.
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