By Nancy Spring, Senior Editor

Wind power’s success story is truly remarkable and like many Hollywood stars, “overnight success” was really the result of years of hard work.

In 2008, the U.S. wind energy industry brought more than 8,500 MW of new wind power capacity online, increasing the U.S. cumulative total by 50 percent to more than 25,300 MW, according to the American Wind Energy Association’s (AWEA) annual wind industry report for year ending 2008. That’s quite a jump from the 2006 yearly total of 2,400 MW.

In its role as a force in the energy industry, wind power’s concerns now move from breaking-in to growth strategies. At the Windpower 2009 conference in Chicago, five main issues emerged that could support or thwart that goal: federal support, transmission constraints, utility system integration, wind farm maintenance and turbine design.

Wanted: Government Support

The year’s largest gathering of wind power enthusiasts began like a political convention. The rallying cry at Windpower 2009, “Yes to RES,” was led by Denise Bode, AWEA’s CEO, who urged the audience to support a strong national renewable electricity standard (RES).

AWEA is calling for a national RES of 25 percent by 2025. The wind industry trade association says a national RES will provide the certainty businesses need to invest in wind power by opening new factories and training new workers. But percentage numbers being discussed for federal climate and energy legislation are beginning to drop.

In May, the House Energy and Commerce Committee’s RES was 20 percent by 2020 and included a provision that allowed states to meet up to 8 percent of the standard through energy efficiency improvements. (Final numbers are still a work in progress. As this is being written, comprehensive legislation goes to the full House for debate.) For AWEA, this was a disappointment.

In a May 22 statement, Bode wrote “such a low level—less than one-half the level originally proposed by President Obama and in Chairman Markey’s original discussion draft—could severely blunt the signal to the private sector to invest billions of dollars and expand production, manufacturing and job creation.”

Regardless of the final outcome of a national RES, wind power enjoys strong support at the federal level. Speaking at the conference keynote session, Secretary of the Interior Ken Salazar said Interior is a “friend of wind” and President Barack Obama its partner. Interior is investing $41 million to facilitate large-scale production of renewables on public lands.

“For the first time in the 160-year history of the Department of the Interior, you have a friend,” he said. “We will open our doors to wise renewable energy on our lands and oceans.”

Salazar said wind could generate 20 percent of U.S. power by 2030. According to Interior’s calculations, there are 1,000 GW of offshore wind power on the Atlantic and 206 GW of potential wind on public lands in the West. Slowing things down is the backlog of wind power project applications. Salazar said there are 25 projects waiting in line in the Western states alone and even more site-testing applications.

Smart Grid, Strong Grid

While an RES is something wind power advocates want, transmission is something wind power needs. Here, too, support from the federal government is strong. Salazar said work is being done on transmission corridors and several new transmission lines may be ready for construction by 2010 to start the “new national super grid.”

Federal Energy Regulatory Commission Chairman Jon Wellinghoff told conference attendees that “wind power is the future and promise of America” but that the transmission grid will have to be upgraded. “The grid is stressed already,” he said, “and as we add wind, it will be more stressed.”

Wellinghoff warned that renewables development may cease unless the grid is rebuilt. He endorses building extra high voltage (EHV) transmission to deliver location-constrained renewable power to distant load centers. Understanding the use and integration of the demand side to stabilize the grid when there are massive amounts of wind is also key; so is enabling consumers by implementing smart grid technologies.

AWEA says inadequate transmission capacity is a significant barrier to renewable energy development and that the nation’s renewable energy resources cannot reach their full potential without renewed transmission infrastructure investment. Plans for interstate 765 kV overhead power lines are now being considered at the federal level.

But siting and building transmission lines is contentious, expensive and time-consuming for the power industry. If increasing wind power’s share of the generation mix from today’s 1.25 percent to 20 percent in 10 years depends on building new transmission lines (an undertaking that would require thousands of miles of 400- to 600-foot-wide rights of way, eminent domain land takings and environmental impact) wind power’s current plans for growth may be stunted.

Besides underestimating the challenge of constructing new transmission lines, competing visions of grid expansion exist and many analysts say cost allocation will be the biggest issue. Other industry experts recommend avoiding wind farm locations that lack firm transmission.

Integration, Forecasting and Load Shape

What does it take to operate a system with high levels of wind? Utilities are becoming more experienced with the special characteristics of wind power as more wind farms enter the grid.

Jay Caspary, director, transmission development, Southwest Power Pool (SPP), is focused on the Western states where wind penetration studies show as much as 95 GW of wind potential. Caspary said the SPP will need storage and transmission. One problem is ramp-up—the speed at which wind goes up at the same time as load goes down in SPP territory. He has seen ramping of 1,800 MW in an hour meaning that “wind and load are out of phase.” Without some way to curtail wind that comes online, reliability will suffer. “We over-sold the system,” Caspary said.

For Bruce Bailey, CEO of wind forecasting company AWS Truewind, ramp events are also becoming a key issue. He is focusing on what kind of sensing technology to install and where to find the ideal places for it so that control room operators can learn to trust forecasting.

“The forecaster has to ‘see’ what’s going on at the wind farm,” said Bailey.

But Pascal Storck, president of global renewable energy forecasting company 3Tier, said the wind industry is experiencing the beginning of diminishing returns on improved forecasting. And Mark Ahlstrom, CEO at wind resource analysis company WindLogics, said renewables are starting to challenge grid management.

“Because of the inherent variability, perfect forecasts are not the issue and won’t solve the problem,” said Ahlstrom. “The real problem of integration is whether or not to continue running the grid the way it’s run now for coal and nuclear plants.”

Low demand is sometimes more difficult to manage than peak demand at Southern California Edison (SCE). SCE spokesperson Barry Gilman said must-take renewables can exceed load. “We have to off-load that power and we’re paying a premium for it. The over-gen situation is critical.”

At SCE, wind forecasting enables the utility to run on a day-ahead basis for scheduling and real-time adjustments can be made 85 minutes ahead of schedule. AWS Truewind provides the data SCE needs to blend wind with its other generation types.

In the ERCOT market, there is a risk that extreme wind generation could cause wholesale tripping of wind units. Problems did occur in February 2007 and February 2008 but Reigh Walling, director, GE Energy, said 80 percent of the time “wind persists and doesn’t change that much.” Most weather events are predictable and ERCOT can carry the needed extra reserves, both spinning and non-spinning.

Maintenance and Reliability

Maintenance is critical at wind farms to ensure reliability. William Needelman, chief science advisor, Donaldson Co., ranked reliability problems for wind turbines in order: gearboxes, blades and generators.

Best practices for gearbox maintenance include using the correct filters and guarding against gear oil contamination. Siemens has been working for 10 years on “gearbox frustration” and the National Renewable Energy Laboratory has started a Gearbox Reliability Collaborative that focuses on gearbox redesign.

New drive train standards are being developed and new technologies for generators include permanent magnet generators that have shown better low speed efficiency and lower maintenance. Fiber optic load sensing technology has been developed that can give the system operator immediate feedback on mass and pitch imbalance, ice detection and turbulence.

Tower fatigue load events can cause shut-down. To find out what causes high levels of tower vibrations, research is being conducted on thrust and wind speed calculations for various pitch angles.

Vibration problems are often caused by rotor imbalance, said Anke Grunwald, marketing and sales engineer, WindGuard North America. Rotor balance can change over time, the result of an uneven distribution of mass that can be caused by wear and tear or manufacturing problems or blades that have absorbed water or been damaged by lightening. Rotor imbalance has an impact on important wind turbine components like the mainframe and the gearbox. Blades can crack and power output will decrease.

Grunwald said the rotor can be balanced, but not with counterweights. To optimize the efficiency of the rotor and maximize the service life of the turbine, Grunwald recommended making repairs as needed and measuring blade angle deviation and mass imbalance using an optical procedure.

Getting Bigger

Designers want to increase wind turbine size by developing new designs that can overcome today’s limitations.

One hybrid tower design uses precast concrete to address highway transportation issues. The tower comes in 3-meter-wide pieces, much smaller than one-piece steel models. Crane time to construct the concrete tower is a few days and, according to Advanced Tower Systems, the towers require no maintenance because there are no bolt connections. Siemens has a 2.3 MW hybrid concrete tower model at its test site in Germany.

New welding and inspection methods are addressing structural limits caused by buckling and fatigue. For offshore towers, construction becomes more complex. There, submerged arc welding (SAW) will be the standard. And as the magnitude of wind turbine loads increases, more attention will be paid to foundations. Tomas Vazquez, management consultant at Sargent & Lundy, said currently no national code exists in the U.S. for wind turbine foundations.

Blades are reaching new lengths. Today, 126 meters is the longest but designers continue to search for methods and materials to break that barrier. Challenges to large-scale blade manufacturing include material handling, resin infusion and bond improvement. Investigation into aerodynamic load and pitch control is ongoing at Sandia National Laboratory (SNL) and helicopter industry research has been applied to the development of new blade concepts.

Airfoil post-stall characteristics are significant for the new larger sizes, said Sandeep Gupta, manager, loads engineering, Clipper Windpower. “Airfoil selection is the most critical aspect of wind turbine blade design.”

What is the optimum wind turbine blade? After presenting information on a fast-prototype blade design, Kristian Dixon at Siemens Wind Power said lots of work still needs to be done. “We just sort of started this.”