Keeping the Electrons Flowing

One of the most popular sections on AWEA’s web site is the projects page, which contains an inventory of wind projects across the nation. It is visited frequently for very good reasons. The tally of new projects is the most tangible indication of the success that decades of legislative, policy and technical-development efforts have had in vaulting the wind industry to the status it holds today.

Likewise, much attention is given — in places ranging from industry conference session topics to coverage in the general press — to the complex process required to create those projects. Determining the wind speeds in a project area, permitting, utility interconnection rights, financing, siting, equipment selection, road building, the process of bringing heavy construction equipment on site — the list goes on. All such development-related topics are crucial to the industry.

But any of us who stop by the local Jiffy-Lube (or get out the mechanic’s creeper in the garage) know that responsible maintenance of complex equipment is absolutely necessary to ensure the original investment remains worthwhile. Though new installations are a proxy for gaging industry progress, long-term productivity — and the operation and maintenance (O&M) functions needed to support that productivity — is vital to achieve the objective of producing clean, non-polluting electricity.

High-tech and robust

A wind turbine is arguably orders of magnitude more complex than the family car, given the state-of-the-art technology it uses to convert wind energy into usable electricity. Sophisticated aerodynamic blade designs efficiently convert the kinetic energy in the wind to mechanical energy via a slowly rotating shaft. From there, a complex gearbox increases the “quality” of that rotational energy and imparts it to a high-speed rotating shaft. The mechanical energy is then converted to electrical power through a specially-designed generator and, finally, the power converter “reforms” the electricity from the wind turbine into the high-quality power that is fed into the utility grid to power our homes.

In spite of that complexity, the wind turbine must perform those functions day in and day out. A wind turbine commonly is producing electricity up to 80% or 90% of the time. But what does that really mean? The analogy of a wind turbine being a combine that harvests the wind 80 meters up in the air often is used. That’s a good analogy in many respects, except that a conventional combine only harvests crops when they are at the right stage of maturity. The farm crew keeps that combine operating day and night to catch the crop at the peak of perfection, a process that may continue for weeks. Still, in the end, the combine may log only 600 hours of operation per year.

Similarly, the “traveling salesperson” who puts 40,000 miles per year on a car is actually sitting behind the wheel and operating the vehicle only 800 hours per year. Compare that to a wind turbine. If it’s operating 80% of the time, it’s producing electricity into the grid 7,000 hours per year. That is tough service.

Some of us remember back a few decades ago when the primary federal policy supporting the increased use of wind power was an investment tax credit-that is, project owners received a credit reducing their taxes based on the cost of an installed wind turbine. While that policy achieved the desired turbine installations in many cases (some of which are still operating today), there were examples of projects that were financially structured to be profitable for the investor as soon as the turbine produced its first kilowatt-hour of electricity. Thus, the incentive to invest in continued operation and maintenance was minimized, resulting in projects with poor performance.

In contrast to the investment tax credit, the production tax credit (PTC) in effect today (after a dubious history of short-term extensions and even expirations) transformed the financial incentive to focus solely on long-term electricity production. An owner receives no tax credit from the federal government until the turbine begins to operate, and then it only receives the credit based on the quantity of electricity produced — over a long period of time! In this way, federal policy makers learned from previous experience and constructed an incentive that resulted in good projects using good turbines, with good support for continued operation. Financial institutions, insurers, and project owners now depend on a continued flow of electrons from the wind turbine to justify their investments, which ultimately provide a reliable supply of electricity to power-hungry customers.

Moving parts

Optimal productivity of a wind turbine requires a partnership among the manufacturer, the developer and the operator. First, components must be designed and built to withstand the severe operating conditions in a wind turbine; moreover, the design must accommodate component replacement and repair in the cramped space that is the nacelle, the box-like structure sitting at the top of the tower where the gears and other equipment reside. The developer, meanwhile, can impact productivity by the layout of the wind farm. If the spacing between turbines is not optimal, the downstream wake of a wind turbine may hamper the performance of other turbines in the array. In addition, the wake may cause turbulence that may increase the stress on components in the neighboring turbines.

Finally, it’s the job of the operator and its maintenance crew to keep those turbines in tip-top shape to squeeze out as much electricity as possible, for as long as possible. Since the turbine is operating the vast majority of the time, the operator must schedule semiannual routine maintenance — during which time the turbine must be taken out of operation — at the best possible times to minimize loss of productivity. In conventional power plants, maintenance workers walk around the generator on a daily basis, checking relevant gauges, temperatures and sounds. That’s not possible with a wind turbine.

The wind industry, therefore, has developed complex “condition-monitoring” equipment to remotely signal the status of each of the operating components inside the turbine’s nacelle. Based on the information gathered, a maintenance crew may need to shut down the turbine and make the climb up the 80-plus-meter tower, possibly in inclement weather, to check on and rectify any abnormal situation. Thus, O&M, like the wind industry as a whole, has matured a great deal over the years. But great industries continuously try to best themselves, and so there inevitably remains work to be done.

AWEA is helping the industry step up to the challenge of wind project productivity; in fact, multiple AWEA departments work directly on O&M issues. Of course, the AWEA legislative team was instrumental in the adoption of the production tax credit fifteen years ago, and they have been the lead advocate for extending the PTC and establishing long-term federal energy policies to ensure the supply of clean electricity into the future.

So, visit your nearby wind farm, marvel at the sleek beauty of those slowly rotating turbine blades, and know that behind those statuesque symbols of a clean energy future is a whole network of people and products that will keep those electrons flowing as long as the wind blows.

John Dunlop is AWEA’s senior technical engineer.

This article first appeared in the December 2007 issue of Windletter and was republished with permission from the American Wind Energy Association.

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