Maintaining Wind Fleets

Salvatore Salamone | Apr 05, 2011

 

Operations and maintenance costs for wind farms have always been thought to be significant. Early Department of Energy studies pegged the costs at between a half and one cent per kilowatt-hour for wind farms in the United States.

Because large-scale deployment of wind turbines had not begun, such estimates, made five years ago or earlier, had great uncertainties because of the limited availability of real-world data. As wind farms have multiplied across the country in recent years, more operators are finding there are hidden costs to maintaining their wind fleets. There are also some promising technologies that might help reduce these costs.

To put the operations and maintenance costs into perspective, consider that wind turbines in the United States currently can produce more than 36,000 megawatts of generating power, according to the American Wind Energy Association. That's if they are working properly. Unfortunately, turbines and their components can experience problems taking them out of commission. Certainly, there can be mechanical problems with generators, gearboxes and blades. Other problems can arise in turbine control systems, electrical systems and with turbine sensors.

Like other electric utility sectors, the largest cost factors in wind turbine operations and maintenance are for parts and labor. Scheduled maintenance and parts repair or replacement are essential, and can be properly budgeted for. Unscheduled maintenance is the cost killer.

What particularly drives wind farm operations and maintenance costs up are the size and weight of a typical turbine. Commonly used turbines in the United States have a tower about 262 feet high, a rotor assembly of blades and hub that weighs about 50,000 pounds, and a generator that weighs in excess of 110,000 pounds. Repairs and routine maintenance require the availability of large cranes and hoists capable of lifting such massive gear. Offshore wind farm operators in other countries occasionally must bring in helicopters to service their turbines.

All of these things add up. As a result, the old Department of Energy estimates of operations and maintenance costs were not far off. In October, Wind Energy Update, an organization that provides news, analysis and business intelligence reports for the wind industry, noted that the average operations and maintenance costs for wind power are about 2.5 cents per kilowatt-hour.

One factor that comes into play is that the brunt of the costs falls on the equipment manufacturers when a turbine or its individual components is under warranty. However, even if these costs are fully covered by the manufacturer, the wind fleet operator still loses revenue when equipment problems occur. When it comes to today's utility-class turbines, each percentage point drop of availability in a year can result in the fleet owner losing up to $500,000 in revenue, according to one industry estimate.

More troubling for wind fleet owners and operators is that many turbines are coming off warranty. The end of last year marked the first time in U.S. history that more wind turbines were operating out of warranty than were covered, according to Wind Systems magazine. And Jon Harman, director, Wind Energy Update, noted that, as of the beginning of this year, "a vast number of operating wind turbines approach the end of their warranty period."

To reduce unscheduled maintenance, turbine manufacturers and wind farm operators are eyeing new technologies to help identify potential problems before they happen.

Most manufacturers have offered remote monitoring capabilities so operations and maintenance staff can observe the state of various wind farm components. And, in fact, turbines have numerous sensors built into them to provide data about the operational state of key elements.

This technology is now being complemented by add-on solutions.

One example is predictive analytic software developed by SmartSignal. The diagnostic software works with supervisory control and data acquisition (SCADA) data from existing sensors on a wind turbine. It compares this data to software models customized for individual pieces of equipment to provide early warning of emerging problems.

Others are offering vibration condition monitoring solutions that try to detect gearbox problems at the earliest stage. There is also add-on technology for ice detection. On the academic front, researchers are investigating ways to mine SCADA data to identify turbine performance patterns that might be used to spot potential problems before they affect operations.

This article originally appeared in the March/April issue of EnergyBiz magazine.

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