US wind energy: Parity with fossil fuels is getting closer

Several times each year, I make the three-hour drive from my home in Indianapolis to visit Chicago. About halfway in the trip, the Meadow Lake Wind Farm (IN, US) appears and stretches for miles in each direction off Interstate 65. It’s a mesmerizing sight, these very long rows of large, white turbines (1.5 to 2.1 MW each), rotating in unison as they harvest the Midwest breeze. There are 303 turbines and 500 MW of capacity. Plans are to double capacity to more than 1 GW in the coming years. Beneath the graceful turbines, the local farmers sow and harvest their crops as they have always done. Some things in Indiana remain constant, even as new technology advances.

The planned expansion at Meadow Lake will depend, however, on a number of factors, one of which could be the nonrenewal of the Production Tax Credit (PTC) by the U.S. Congress. The PTC expired at the end of 2012, was temporarily renewed in 2013, and then expired at the end of 2013, only to be retroactively renewed for 2014 with two weeks to go in the year. The PTC provides a tax credit of $0.023 per kW/hr, enabling wind energy to be more competitive with electricity generated by fossil fuels. According to the American Wind Energy Assn. (Washington, DC, US), US wind energy capacity increased by a record 13 GW in 2012, but the annual increase dropped to only 1.1 GW in 2013, recovering only a little in 2014 to around 5 GW. The current belief is that the PTC will not be renewed for the foreseeable future. By contrast, European and Asian governments have much more stable energy policies concerning wind power, and installations in those regions have been fairly steady over these same years.

So is the wind energy industry in the U.S. headed for extinction? A recent report, Wind Vision: A New Era for Wind Power in the United States, issued by the Wind and Water Power Technologies Office of the US Department of Energy (DoE), offers reasons for optimism, even without the stimulus provided by the PTC. The report notes that wind energy provided 4.5% of US energy demand in 2013, up from only 1.5% in 2008. Both Iowa and South Dakota now generate more than 25% of their needed electricity from wind. Improved designs and larger rotors have reduced generation costs from $0.071 per kWh in 2008 to $0.045 per kWh in 2013 for regions where wind speeds are reliable. The report projects a further 24% reduction by 2020 and 33% by 2030 based on improvements in turbine technology and operations. These kinds of improvements might give natural gas, even with its current low market price, a real challenge. The DoE envisions that wind will meet 10% of U.S. demand for electricity by 2020, 20% by 2030 and 35% by 2050. These are some pretty aggressive targets.

Readers of this magazine know that builders of wind turbine blades are substantial users of composite materials, so this level of growth bodes well — if it happens. I visited a major wind blade factory in February, getting the in-depth tour engineers crave. I was able to witness every step of the manufacturing process for blades that exceed 50m in length, so we are talking large tools and very large parts. Having visited factories making large carbon fiber aircraft components and high-volume SMC automotive parts, I was immediately struck by how different the manufacturing process is for turbine blades. Teams of people move from mold to mold, laying fabric and core by hand, then bagging the part for resin infusion. Adhesives are applied manually rather than robotically. Tolerances for fiber angle and bond thickness are much more lenient than in aerospace. Nonetheless, what comes out of the factory is a very robust, durable product that is designed to operate for 25 years or more. While one might think automated fabric layup and adhesive application would be a natural fit, cost analysis has determined that such machines would have to lay up well over 1 MT per hour to be competitive with manual labor.

So what is likely to drive the costs of wind energy down? From the blade perspective, several technologies have promise: Building longer but segmented blades (to overcome current transport limitations) and joining them at the installation site; low-cost, high-volume carbon fiber for critical stiffening elements, such as spar caps, especially as blades get longer; improved modeling and simulation to optimize design and reduce material usage yet maximize performance; and the use of high-speed NDE techniques to ensure quality. 

As it turns out, cost (especially that of carbon fiber), modeling, simulation and NDE are basically the same issues aerospace and automotive engineers face. Maybe not so different after all?