Modern wind turbines can be extremely reliable, with the percentage of time that many systems are available to produce power (often called   "availability") often being 99% and more. This article, contributed by a test engineer, puts the reliability expected of a wind turbine into perspective by comparing it with that of an automobile. Another perspective is provided by comparisons with helicopters, the rotor blades of which must often be replaced after several hundred hours, while wind turbine blades commonly last 10 to 20 years and more.

Wind Turbine Life and Reliability

Contributed by Eric Eggleston

If you were to drive your car an average of 50 mph, 100,000 miles would come to 2,000 hours of engine run time. Probably the average speed is much lower and the engine may actually get perhaps 3,000 hours. During that time, you would expect to change the oil 20 times, tune-up perhaps 10 times, change the timing belt once or twice, and wear out two sets of tires. Last I looked, the record for a Mercedes diesel in the US was about 900,000 miles before engine replacement. An admirable feat! Reduced to engine hours, I would guess 27,000 hours.

At the U.S. Department of Agriculture test site in Bushland, Texas, our 40-kW Enertech turbine runs about 60% percent of the time (when the wind is high enough to make power). Running 60% of the time with 8,760 hours in a year, 3,000 hours of operation takes about seven months. The life of the record-making Mercedes would get surpassed by the Enertech in five years, two months. Yet the turbine is still running after 15 years of almost continuous operation. We had to change the yaw bearing twice (I think it's a design defect -- the bearing is just too small) which made us take the turbine off the tower. At those times, we replaced seals, changed oil, and other maintenance. And this turbine was an early production model, and is not the best, most reliable model currently available.

Yet, our 40-kW Enertech has been operating since 1982 with about 97% availability (3% down time) over 52,000 hours of operation (as of February, 1998). The most trouble-free car on the market would pale in comparison to what is regularly expected and demanded of wind turbine life and reliability.

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