Pattern Energy Group Inc. said it has started work to repower its Gulf Wind facility in Kenedy County, Texas.

Work there will consist of removing the current wind turbines and replacing them with 118 Siemens Gamesa SWT-2.3-108 turbines. Following the upgrade, the wind farm will have a total generating capacity of 271 megawatts (MW).

The repowered facility is expected to have more efficient production, lower operating costs, renewed production tax credits (PTCs) and a longer service life.

The repowering project consists of replacing nacelles, towers and blades for the 118 turbines. The new turbines have 108 m long blades on 80 m towers.

The Gulf Wind facility entered into a new 20-year power purchase agreement with Austin Energy for most of the facility's energy production. The remaining output is expected to be sold at merchant power prices.

Growing market

The Gulf Wind project is the latest in a string of wind turbine repowering projects. The National Renewable Energy Laboratory has indicated that annual U.S. wind repowering investment has the potential to grow to $25 billion by 2030.

Rocky Mountain Power is upgrading around 900 MW of wind generating capacity in Wyoming with larger blades, better control systems and other technology. The repowering is expected to increase the energy production of the wind projects by 11% to 35%. The $1 billion in upgrades are planned to be complete by the end of 2020.

Similarly, MidAmerican Energy in 2017 awarded a contract to GE Renewable Energy to repower as many as 706 older turbines at several wind farms in Iowa. After repowering, each turbine is expected to generate between 19% to 28% more electricity.

The case for repowering

The Energy Department's Energy Information Administration (EIA) said that fully repowering wind turbines typically involves decommissioning and removing existing turbines and replacing them with newer turbines at the same project site. Full repowering has mostly occurred in California, where many turbines were installed before 1990.

Partial repowering involves leaving some portion of the existing wind turbine and replacing select components. By partially repowering a site, EIA said that owners can increase hub heights and rotor diameters to produce more energy.

Wind turbines are designed to have lifespans of between 20 and 25 years, but wind capacity factors decline with age as mechanical parts degrade. Research suggests that, on average, wind turbine output declines by 1.6% each year.

Newer turbines tend to rotate much more slowly and quietly than older, smaller turbines, turning at 10 to 20 revolutions per minute (rpm) instead of 40 to 60 rpm. Slower wind turbine rotations can ease issues such as bird mortality and shadow flicker.

Repowering wind turbines may present some challenges. For example, the EIA said that the risk of failure may increase when reusing components such as towers and foundations that were designed for smaller turbines. Other challenges may include renegotiating power purchase agreements, grid interconnection agreements and property leases.