Repowering older wind turbines, which involves replacing aging turbines or components, is becoming more common in the United States as the turbine fleet ages and as wind turbine technology advances. Newer turbines tend to be larger and installed at greater heights, allowing for more capacity per turbine. About 12% of the wind turbines in the United States were installed before 2000, but these turbines make up only 2% of the installed wind electricity generating capacity. Federal production tax credits provide an incentive to increase electricity generation from existing wind turbines. In December 2015, the production tax credit (PTC) was extended until the end of 2019. The four-year extension and legislated phase-out of the PTC is expected to encourage many asset owners to repower existing wind facilities to requalify them to receive another 10 years of tax credits. […]