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Bigger and Better: Lab Aims to Improve Giant Wind Turbines

February 5, 2009

If the U.S. is going to generate 20 percent of its electricity from the wind in the next 20 years, wind turbines will need to evolve in every way - larger, taller, less expensive, more reliable and more efficient.

At NREL's National Wind Technology Center, engineers are preparing to install the two largest turbines ever tested at the laboratory. Key elements of a 1.5 MW General Electric turbine have begun arriving; instrumentation and equipment testing should begin by late summer. Installation of a 2.3 MW turbine from Siemens Power Generation is scheduled for late summer, too.

Both turbines will be erected on the NWTC's eastern perimeter, where they will run for years while serving as prominent sentinels overlooking metropolitan Denver.

"We need to understand how these big turbines respond," said senior project leader Jim Green, who is leading the GE tests. "Increasing their performance, reducing their loads, creating components that last longer – we'll need to learn about all those things if we're going to make more wind power."

Supersized Wind Turbines

The GE turbine will operate atop a 262-foot steel tower. The diameter of its rotor will reach 250 feet. Its total weight, including the tower, will approach 220 tons.

The only visible part of the foundation will be the bolt circle for the tower itself, but looks can be deceiving. Covered with dirt for extra weight, its octagonal concrete foundation pad will measure 50 feet across and weigh about 500 tons.

"The pad has to be that big," Green said, "because that's what keeps the whole thing standing upright in high winds."

Special overland trucks started arriving at the NWTC in December carrying sections of the GE system. The trucks are up to 195 feet long – three times as long as a typical 18-wheler. They use as many as 13 axles to distribute the weight of their huge cargo.

The trucks took a designated route on major roads that are designed to handle oversized loads and traveled at times that would not disrupt traffic. Two of the trucks were followed by a separate escort vehicle that remotely steered the trailer's rear wheels by radio signals to help the long trucks negotiate tight corners.

In mid-December, the tower sections arrived from Tulsa, Okla.; the blades from Aberdeen, S.D.; and the generator housing and rotor hub from Pensacola, Fla.

During the spring, NREL will build new access roads to the planned turbine pads and provide other site preparation. NREL is purchasing the turbine for the U.S. Department of Energy under a subcontract with GE.

The GE turbine is already a workhorse commercial model, accounting for nearly half of all turbine sales in the U.S. The NREL tests are intended to discover ways to squeeze more power out of existing wind farms and improve the durability of the turbine's components.

"Any improvements we can make will have a lot of leverage in the wind industry," Green said.

Bigger than a Football Field

The Siemens 2.3 MW turbine will be noticeably larger than the GE. It will use a similar tower, but its rotor diameter is a whopping 331 feet – more than the length of a football field!

Unlike the GE, the Siemens model is a late-stage prototype. It features a novel blade design that captures more of the wind's energy, but is not supposed to force any more load onto the turbine's moving parts and control systems. It will be heavily instrumented to produce a constant stream of data on aerodynamics, power characteristics, vibrations, system fatigue, acoustics and other key measurements.

The tests will be conducted in three phases through late 2011.

"These tests will verify the performance of the new blades under real and challenging conditions," said NREL senior engineer, Lee Jay Fingersh, who is project lead for the Siemens turbine.

"It looks very graceful and simple, but the aerodynamics of a wind turbine are harder to understand than an airplane or a helicopter," he said.

Siemens is providing the turbine, engineering support and maintenance from its new R&D office in nearby Boulder. NREL is providing the site, installation services and expertise in field aerodynamics testing, structure and reliability testing and meteorological analysis.

The NWTC would make a poor commercial wind farm, but the location downwind from Eldorado Canyon and the Continental Divide provides gusty conditions that challenge turbine and blade designs and generate data at the equipment's limits. Motorists on Highways 93 and 128 can expect to see the giant turbines operating regularly.

"The turbines generate more power than we can use at the NWTC," Fingersh said. "We'll become an exporter of electricity and be able to offset some of the program's costs."