Research Evaluates How U.S. Wind Plant Performance Changes with Age

A recent study from the U.S. Department of Energy’s (DOE) Lawrence Berkeley National Laboratory shows wind plant performance decline because of plant age in the United States can be partially managed and is influenced by policy. Compared with studies of how European wind fleets age, the U.S. wind fleet shows mild performance loss with age, and plants built after 2008 show the lowest levels of performance decline that have been found in a major fleet.

The United States is currently the second-largest wind power market globally, supplying 7.3% of the nation's electricity generation in 2019. Yet, this is the first research effort to evaluate the impact of plant age on the performance of the U.S. wind fleet.

A team of researchers in the Energy Analysis & Environmental Impacts Division at Berkeley Lab analyzed the performance of 917 onshore wind projects in the United States. The team found U.S. wind plants maintain 87% of peak performance after 17 years and newer plants show almost no decline over the first 10 years.

To model the projected growth of wind power and determine the financial viability of wind plants, researchers and investors need to take into account wind plant degradation over time. Studies in Germany, Sweden, and the United Kingdom have shown that differences in each region's weather, geography, and policies, as well as differences in technology can impact wind fleet performance over time.

The findings of the study further show that the U.S. wind fleet performance decline per year is on the low end of the range found in Europe. The studies conducted in Europe, however, found that performance declined linearly over time, whereas in the United States, the degradation does not happen smoothly over time. Instead, Berkeley Lab found a more abrupt change in the performance of U.S. wind plants after 10 years of operation, which also coincides with when U.S. wind plants lose eligibility for the production tax credit (PTC).

In the United States, the PTC was implemented as part of the Energy Policy Act of 1992 to incentivize wind power development and installation. The PTC provides wind plants with a production-based tax credit for their first 10 years of operation and the authors of the study suggest that the 10-year duration of the PTC impacts the performance degradation rate of U.S. wind plants.

"We hypothesize that after wind plants lose eligibility for the PTC, they may choose to spend less on maintenance overall and their performance may therefore drop," said Research Scientist Dev Millstein, an author of the study. “So, a sort of 'bonus' effect of the PTC policy is that operators may be keeping their plants running at peak performance while the policy is active."