Wind-power capacity in the United States continued to experience strong growth in 2017 due to the production tax credit, various state-level policies, and improvements in the cost and performance of wind-power technologies, yielding low-priced wind energy for utility, corporate, and other power purchasers.
Here are the top four wind market industry trends of 2017, according to the Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE).
1. Improved wind-turbine performance
The average capacity factor, which is a measure of how close a plant is operating to its maximum output, among projects built from 2014 to 2016 was 42%, compared to an average of 31.5% among projects built from 2004 to 2011. This represents a 33% increase since 2004 to 2011 and a 79% increase since 1998 to 2001.
Improvements in design engineering and manufacturing have led to higher hub heights and larger rotors, which are comprised of turbine blades and the hub.
The increased size of these components has contributed to the trend of higher capacity factors. Turbines with larger rotors have higher capacity factors because the spinning blades sweep a larger area resulting in greater energy capture. Using a taller tower to increase hub height at sites with positive wind shear, those where wind speed increases with height, helps lowers the cost of wind energy by providing greater access to higher wind speeds.
2. Turbines originally designed for lower wind speed sites dominate installations
Large, powerful wind turbines with long blades were originally developed to be deployed in less windy areas, where other more conventional wind turbines would be less economical because they could not generate a lot of power from the limited wind resource. These wind turbines have low “specific power,” which is a measure of the nameplate capacity (in watts, abbreviated W) divided by the rotor swept area — the area that the blades sweep while they spin (in square meters, abbreviated m2).
While turbines with low specific power were originally designed for lower wind speed sites,they have increasingly been installed across the country, even at sites with high wind speeds because they have been found to be cost-effective in a variety of wind speed regimes. Growth in the rotor diameter (green circles) — and therefore the area that it sweeps (in m2) — has been particularly rapid, as turbines have been installed with longer blades.
At the same time, there has also been a modest increase in average nameplate capacity (blue bars). These larger rotors have helped to drive a decline in the average “specific power” among the U.S. wind turbine fleet over time, from 395 watts per square-meter among projects installed in 1998 to 1999 to 231 W/m2 among projects installed in 2017.
3. Partial repowering of wind projects
Partial wind project repowering is when major components of older turbines are replaced with more advanced turbine technology in order to increase energy production. This extends project life, and the repowered portion may also be eligible for tax incentives. In 2017, wind developers repowered 2,131 MW of capacity by retrofitting 1,317 turbines. Upgrades included increasing rotor diameters (longer blades) and replacing major nacelle components.
4. Multiple turbine configurations
Nearly one-fourth of the larger wind projects built in 2016 and 2017 used turbines with multiple hub heights, rotor diameters, and/or capacities — all of which were supplied by the same original equipment manufacturer (OEM). While there are several possible explanations for this trend, there is an increasing willingness among turbine suppliers to provide multiple turbine configurations, which leads to increased site optimization for maximum energy capture.
A second possible explanation involves how developers commonly qualify for the Production Tax Credit — ordering some wind turbines prior to the deadline needed to qualify for the tax credit, and then months later ordering the remaining turbines which by then might feature slightly different characteristics, like a larger rotor.
Learn more about market trends and developments in wind technologies by visiting DOE’s 2017 Wind Technologies Market Report.
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