The wind industry remains in a strong growth mode but various challenges loom, including transmission constraints and turbine scale-up.
By: Jason Makansi, Pearl Street Inc.
Getting the federal production tax credit (PTC) renewed, for more than the time it takes to help re-elect a presidential candidate, is a solid accomplishment for the U.S. wind industry. However, other challenges loom, most notably in transmission and turbine/generator scale-up, which could frustrate the industry even more as it seeks legitimacy for generation capacity additions.
At the American Wind Energy Association (AWEA) annual conference and exposition in May, held in Denver, the broad issue of managing the impact of larger percentages of wind energy on the T&D grid seemed to garner the spotlight, both in the general and technical sessions. In addition, leading project developers, owner/operators, and suppliers hinted that rapid scale-up of turbine designs may not be the panacea for reducing wind’s cost of electricity (COE).
Wind still clearly enjoys strong public support at the grass roots. More states are designing subsidies to support or encourage wind projects, a growing number of utilities are participating in these projects, new and stronger developers have entered the fray, and the investment community is clearly more interested in its long-term prospects. As one speaker put it, it’s still a double-digit growth market. Not many of those exist in the power industry. However, there was a dichotomy between the political and industry rhetoric. Why?
For one thing, natural gas prices seem to have stabilized and are even trending down. Mike O’Sullivan, senior vice president for development, FPL Energy, conceded that lower gas prices could destroy demand for wind. For another, capital costs for wind projects have reversed course and are now clearly going in the wrong direction. Because of higher commodity costs (affecting all infrastructure businesses), lack of U.S. wind turbine manufacturing, poor exchange rates, and the yo-yo of the on-again, off-again PTC, industry leaders report that the capital costs have increased from as little as $1,000/kW to as much as $1,500/kW. Terry Hudgens, president and CEO of PPM Energy Inc, stated that the inconsistency of the PTC alone adds 20 percent to wind’s COE. Mark Little, VP Power Generation, GE Energy, also confirmed that “COE seems to have plateaued.”
Turbine/generators are clearly getting bigger; and the attendant economies of scale are supposed to help reduce capital costs. Andreas Nauen, President, Siemens Wind Power Division, cautioned that economies of scale “can fall apart,” and that some new wind machines being pushed into the field “are only prototypes.” Informed industry observers should recall the experience in the 1990s with the scale-up and rapid commercial penetration of advanced gas turbines to understand the implications here. Plus, as others pointed out in technical sessions, larger machine components, especially blades, begin to pose transport problems and site-assembly costs.
Grid interconnection issues seemed to occupy much of the “air” at the AWEA meeting, even with the politicos. Congressman Mark Udall (D-CO) noted that “knots surrounding transmission need to be untied,” AWEA Executive Director Randall Swisher listed transmission constraints as the number two challenge behind inconsistent federal policy, and PPM Energy’s Hudgen’s called it a “difficult transmission environment.”
The Federal Energy Regulatory Commission (FERC) relieved some of the burden shortly after the AWEA meeting by finalizing the “Grid Interconnection Rule for Large Wind-Power Facilities.” This rule standardizes interconnection requirements around the country, to some degree anyway, with the following provisions: If the transmission service provider demonstrates they are needed, wind facilities larger than 20 MW must (1) remain operational during voltage disturbances on the grid, (2) meet the same technical criteria for providing reactive power to the grid as required by conventional large generators, and (3) provide for supervisory control and data acquisition to ensure appropriate real-time communications and data exchanges between the wind power producer and the grid operator.
The bottom line is that, now that wind farms are getting larger and are expected to be a larger fraction of the online capacity, they have to meet utility-grade interconnection requirements. Such grid standards are now prevalent in Europe, and regional transmission organizations (RTO) in the United States have adopted specific standards.
According to a presentation by Ernst Camm, S&C Electric Co., low-voltage ride through (LVRT) can be provided through turbine modifications or dynamic VAR compensation devices, including inverter-based devices, power electronically switched capacitors, and static var compensators (SVC), used in conjunction with mechanically switched capacitor banks. In essence, the D-VAR devices provide enough extra time to bring on the capacitor banks in the event of a voltage disturbance. S&C contends that turbine-side modifications are not sufficient to meet the requirements for LVRT. A technical presentation from Siemens seemed to validate this conclusion, with the statement: “Significant dynamic VAR support (SVC or STATCOM) may be necessary.”
Another facet of the grid interface challenge is forecasting how much wind energy, and therefore power output, will be available at a given time. The idea is that, with good forecasting, grid operators can make adjustments to accommodate wind. Mark Ahlstrom, CEO of WindLogics Inc, reported on Xcel Energy’s program to model the impact in 2010 of 15 percent wind penetration on reliability and ancillary services costs to the Xcel North grid. A key objective is to optimize the way wind forecasts are integrated into the control room environment. Analyses by Michael Milligan, National Renewable Energy Laboratory (NREL), suggest that wind does impose additional load following requirements at hourly time scales and underscores the importance of having “fast-moving generators” in the portfolio. However, geographically dispersing the wind resources can reduce ramping requirements.
Robert Gramlich, a former FERC official now AWEA’s Policy Director, summed up the transmission conundrum this way: We need to “use more of the grid and get more grid to use.” While lack of transmission expansion plagues the entire electricity production and delivery value chain, it stunts wind power even more because the best wind resources are where the load isn’t. Milligan, in a later presentation with Damian Berger, Peak Power Engineering Inc., noted these barriers to financing wind projects: Firm transmission service capacity in the west is scarce, non-firm contracts are currently limited to one year, and wind farms and transmission infrastructure pose different development and construction time frames. Further, “high level path analysis shows potential for an innovative tariff” that could help optimize the use of existing transmission resources in at least one area, north and west of Denver.
Transmission planning must also factor in some significant legislative commitments to wind. California officials, for example, envision 20 percent renewable capacity online by 2017, perhaps as early as 2010. Close to half of the requirement could come from the Tehachapi area-if transmission capacity was available-where 730 MW of wind currently operates. Dave Olsen, of the Tehachapi Study Group, reported on recommendations for phased development of wind generation and transmission to meet state policy. One concept is the “renewable energy trunk line,” essentially a new category of facility that would be treated as a “network upgrade” with costs rolled into rates for all customers.
In the east, PJM reported that it has successfully integrated 386 MW of wind; however, close to 4,000 MW is in active planning. West to east power flow constraints could inhibit projects, according to William Whitehead, general manager, system planning. In general, and in contrast to the California approach, PJM seeks to make wind integration more amenable to merchant power economic planning solutions.
As turbines get larger, the critical blade component of the machine requires advanced designs and materials. David Hartman, Technology Leader, Owens Corning, listed the following wind turbine blade design issues:
- Half of the wind turbine blade field failures are caused by natural events or system integration deficiencies (Figure 1).
- Half of the blades tested at NREL over the past 12 years exhibited premature fatigue failure resulting from blade design or manufacturing details (Figure 2).
- Lower weight materials with improved damage tolerance are needed for blades greater than 60 meters in length.
- Material loads rarely exceed 25 percent of strain capacity in static and fatigue testing before a blade failure occurs from design or manufacturing deficiencies.
NREL root cause analyses of failures due to design or manufacturing details reveal that 26 percent of failures result from manufacturing process variations, while 50 percent of failures result from poor design of the joint or laminate.
To put the blade scale-up in context, the 5 MW machine referenced in the sidebar includes a rotor diameter of 126 meters and three 18-ton, 61.5-meter blades; the 3.6 MW prototype includes a 107-meter diameter rotor. Latest commercial production machines, such as the 1.5 MW units being installed for FPL Energy in Oklahoma, include an 83-meter diameter rotor, while a 2.0 MW machine popular in Europe has a 39-meter, 7-ton blade. The next generation of machines, anticipated to be from 5 to 12 MW output, could have rotor and blade diameters twice today’s sizes.
The message appears to be that beyond 4 MW to 5 MW individual machine sizes, blade materials and designs will require significant RD&D and field verification.
To avoid cost impacts from unexpected occurrences in the field and ensure a competitive COE, officials from WindForce GmbH advocated what they call Fibradapt, a technology that embeds fiber-optic strain gage sensors in the blades with sensor signals tied back to the pitch control system. In other words, real-time loading on blades acts as an input signal to the turbine automatic control scheme.
Technical issues aside, the short-term prospects of wind energy ride on the legislative framework. In addition to the PTC, there is the Renewable Portfolio Standard (RPS), left out of the energy bill. AWEA’s Swisher lamented that “the White House does not support a federal RPS.” This, despite the fact that President Bush and the Congress extended the PTC (through January 2006) last year in October, just ahead of the election. However, apparently 65 Senators would support a federal RPS, noted Senator Ken Salazar (D-CO) in the opening session. On top of this support, 18 states and the District of Columbia have passed various forms of an RPS.
Only time will tell whether these are bumps in the road or roadblocks. But like gas-fired generation in the 1990s, wind energy seems to be the one option that all stakeholders can at least compromise around. State programs inch forward as a consistent national framework languishes, not unlike competition and deregulation programs in the 1990s. The foundation for the irrational exuberance in gas-fired projects of 1997-2001 wasn’t laid overnight, and it won’t with wind either. But wet your finger, stick it in the air, and you can sense a coming boom in wind plant construction. Hopefully, the aftermath years of 2002-2005 won’t be the price the industry has to pay this next time around.
Turbine Tech Talk
Some of the notable developments reported at the AWEA conference for large wind turbines include:
- RePower Systems AG leads in the output category with a 5 MW machine, and expects to build five such units in 2006, one to be demonstrated on an oil/gas extraction platform owned by Talisman Energy.
- Siemens Wind Power A/S has developed and is testing a 3.6 MW prototype machine that it expects to be in serial production in 2006. As an indicator of the structural and stability issues big turbines raise, the company noted that the maximum blade tip deflection for the 107-meter rotor diameter is 11 meters.
- EcoTecnia, a Spanish wind turbine supplier, developed a 3 MW model this year targeted for on-shore applications, featuring a change from stall to pitch speed control and a shaft separation concept that “isolates the drive train.”
- Clipper Windpower Inc., with Department of Energy (DOE) funding, has developed an advanced 2.5 MW model targeted for low-wind-speed areas. To be operational this year, it features multiple generator drive output, mega-flux permanent magnet generators, variable speed operation, and a “complex pitch control system.”