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US Wind Power Plants Show Little Decline With Age

Some days if feels like things aren’t made to last. Cell phone replacements, for one — how many does one have to have? Wind turbines, however, show a refined aging that suffers little efficiency loss over time.

Some days if feels like things aren’t made to last. Cell phone replacements, for one — how many does one have to have? Wind turbines, however, show a refined aging that suffers little over time.

Researchers from the Lawrence Berkeley National Laboratory have published a report in the journal Joule that concludes that wind turbines in the United States remain relatively efficient over time. The report, “How Does Wind Project Performance Change with Age in the United States?” (PDF), shows only a 13% drop in performance over 17 years. The researchers point out that newer plants are proving even more consistent and efficient.

Interestingly, the report also points to the positive effect of the US production tax credit (PTC). It is an effective incentive to maintain the plants during the 10-year window in which they are eligible to receive it. The study notes that when this tax credit window closes, wind plant performance drops.

Wind power in the United States now supplies a vital portion of the nation’s electricity. The report highlights that in 2019, wind power supplied 7.2% of US electricity generation.

Wind power will continue to expand. It is one of the most effective and affordable power supply options, maybe even #1 in those regards. Researchers Hamilton, Millstein, Bolinger, Wiser, and Jeong evaluated 917 wind turbines in the US onshore wind fleet. Long-term performance of wind plants is an essential factor in determining their levelized cost of wind energy (LCOE), which basically means the price per unit of electricity produced over a long period of time. However, the rate of performance decline for wind turbines had not been well established in the United States.

The report summary explains, “We find the rate of performance decline to be 0.53%/year for older vintages of plants and 0.17%/year for newer vintages of plants on an energy basis for the first 10 years of operation, which is on the lower end of prior estimates in Europe. Unique to the United States, we find a significant drop in performance by 3.6% after 10 years, as plants lose eligibility for the production tax credit. Certain plant characteristics, such as the ratio of blade length to nameplate capacity, influence the rate of performance decline. These results indicate that the performance decline rate can be partially managed and influenced by policy.”

Chart via Joule (PDF)

“This study addresses the research gap identified above by analyzing the performance of 917 onshore wind projects across the contiguous United States (Figure 1). The sample size of wind projects in this study is much larger than the sample sizes in previous work in the European countries, as we analyze a fleet that is roughly an order of magnitude larger, in terms of installed capacity, and which spans a dramatically larger geographic area that encompasses many different climates. It builds on the methods and approaches of the European research efforts to quantify the performance trends of the US onshore wind plants. We pay particular attention to issues that are unique to the US market, such as the effect of policy mechanisms, including the production tax credit (PTC), on performance trends. We were able to remove the effects of the market-based curtailment of wind plants by producing new estimates, informed by market price signals, of plant-level curtailment. Finally, we explored the influence of plant characteristics on the rate of performance decline through a multivariate analysis. The results from this study help clarify the rate of performance decline across the US wind plants, while also providing insight into how the impact of age on fleet performance has changed with newer wind power technology and how policy and market factors can impact performance outcomes.”

“Map of the 917 Onshore Wind Plants Included in the Analysis Older (pre-2008 commercial online date) plants are shown in pink, and newer plants in orange. The size of each dot is proportional to the nameplate capacity of the plant. The background map shows the annual average wind speed (m/s) at 80 m above surface level.” Map and caption via Joule (PDF).

After 17 years, the researchers found that performance declined, on average, to 87% of year-2 performance.

“Newer plants are defined here as those that came online in 2008 or later. This cohort of plants experienced only slight, though still statistically significant, degradation at a rate of −0.06 cfpp/year (−0.17%/year).”

“The Results of the Fixed-Effects Regression Shown for Old (n = 186) and New Plants (n = 731) Separately. The fixed effects and trends are normalized by the average capacity factor found for the second year after commercial online date for each cohort. All slopes shown have a p value less than 1E-5.” Image and caption via Joule (PDF).

For more, the full report and findings can be found here.

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Cynthia Shahan started writing after previously doing research and publishing work on natural birth practices. (Several unrelated publications) She is a licensed health care provider. She studied and practiced both Waldorf education, and Montessori education, mother of four unconditionally loving spirits.


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