EPRI Study Reveals Ways to Improve Turbine Reliability and Accuracy of Performance Projections
Global wind generation capacity has increased by six times over the last decade. It is projected to triple over the next decade and increase six-fold by 2050. Along with this growth in capacity, advances in wind turbine controls are enabling wind plant owners and operators to use manufacturers’ software upgrades to boost turbine power ratings. Such practices are common in an industry dominated by independent power producers selling energy through power purchase agreements that aim to maximize energy. While this practice (also known as uprating) can increase power production by as much as 5% short term, EPRI researchers have found that it can adversely impact long-term turbine reliability and economics.
“Increasing power rating means more production and revenue initially, but it puts more stress on a turbine’s components and may reduce its lifetime,” said Brandon Fitchett, who manages wind generation research at EPRI. “The amount of component fatigue depends on the magnitude of the rating change as well as site wind conditions.”
Another common practice among developers, owners, and operators is to assume a plant lifetime of 25 years in cost projections without accounting for the site’s wind conditions. These generic assumptions along with the uprating practices can increase the risk that plants do not meet long-term performance expectations.
The EPRI team used a state-of-the-art wind industry aeroelastic model to simulate power rating changes and various site wind conditions, calculating loads on a turbine’s major components, such as the gearbox. This is the same type of model that site developers and owners use to verify and certify turbine designs and projected lifetimes. A second model examined how uprating and site wind conditions impact operations and maintenance (O&M) costs.
The main takeaway: Both power rating and wind conditions significantly impact turbine lifetime and O&M costs. For instance, increasing power rating by 7% could reduce gearbox lifetime by 10 years. Sites with high levels of turbulence could have half the gearbox lifetime relative to sites with low turbulence. A gearbox failure can cause an extended outage of a wind turbine, require a tall crane to replace the gearbox, and cost a few hundred thousand dollars or more in repairs and lost generation revenue.
“Slight decreases in wind turbine power rating can significantly reduce major component fatigue and significantly increase turbine life,” said Fitchett. “If you expect your gearboxes are going to fail early, you may want to consider adjusting your power rating to extend the life of your turbines and reduce O&M costs.”
Plant owners can use the study’s results to create more realistic O&M budgets each year and set more realistic performance expectations over a turbine’s life. Along with other EPRI research on component monitoring and reliability, the insights in this study can inform developers in selecting windfarm sites and component suppliers and in projecting component lifetimes.
“Most developers assume a 25-year lifetime when modeling the long-term economics of proposed wind power sites,” said Fitchett. “This research indicates that they need to adjust that number based on rating and site conditions.”
According to Fitchett, as wind generation grows and coal generation declines over the next decade, the operational strategies of wind plant owners are likely to shift from maximizing generation to providing reliable, flexible output and ancillary services. Indeed, keeping some wind farm power output in reserve could support a more reliable future power grid as well as a more reliable, longer-lasting wind farm.
“In 5 to 10 years, wind farms will likely need to be more flexible and dispatchable, with grid operators making broader use of curtailing wind power to balance the grid,” said Fitchett. “When turbines are not running at maximum potential power, they’re actually providing operators with a valuable grid service—grid-connected reserve power ready for immediate delivery.”
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Artwork by MCKIBILLO