It’s known that ice accumulation on wind turbine blades can cause problems, but a new study from an Iowa State University professor and his research team shows just how much ice can grow on a blade, and how much that can reduce the performance of a turbine.
Some politicians, pundits and internet users overstated the extent to which frozen wind turbines contributed to the recent catastrophic power grid failure in Texas. Ice on blades was, however, one more problem among several larger issues that led to a diminished energy supply that could not keep up with a huge spike in demand.
Iowa State’s Hui Hu had already for years been studying the effects of ice on wind turbine blades. Hu is ISU’s Martin C. Jischke Professor in Aerospace Engineering and director of the university’s Aircraft Icing Physics and Anti-/De-icing Technology Laboratory.
Hu’s been doing laboratory turbine blade-icing studies for about 10 years, according to a news release from ISU’s news service, but getting access to study working wind farms was more difficult.
He ultimately found that access in China, where operators of a 34-turbine, 50-megawatt wind farm on a mountain ridgetop near the East China Sea agreed to a field study in January 2019.
What he found there – using drones to photograph blades after up to 30 hours of exposure to cold and wet conditions similar to those Texas faced – was that ice almost a foot thick built up near the tips of blades and reduced power production up to 80%.
Hu explained that ice can negatively affect a wind turbine in more than one way. The reduced aerodynamics of the blades can mean not enough force is generated to get them to spin, or – because ice does not develop evenly across the blades – the turbine can become off-balanced, generating forces that damage internal workings and require a shut down if those forces exceed certain limits.
In Iowa, he said “Wind turbine icing is an issue, but it’s not that big an issue,” in part because not all ice is the same.
Iowa’s typically cold but dry winter conditions lead to the development of rime icing, whereas more water in the air causes glaze icing, he said. Glaze icing more seriously affects the aerodynamics of turbine blades.
Hu said wind turbines in Iowa may lose 5% or 10% of their power production capability in icy conditions – nothing close to 80%.
That’s also due to wind turbines in colder climates having been winterized. There are temporary solutions for iced turbines that are not winterized, he said – such as spraying hot water from a helicopter – but one-time measures become costly to repeatedly use over time.
Does climate change threaten Iowa’s wind turbines with ice?
While Iowa’s wind turbines didn’t face the same degree of problems as those in Texas did during the same cold snap this year, Iowa is much more dependent on its turbines.
Texas produces more wind power than Iowa – more than any state – but that electricity sourced from wind is 20% of all the power generated in Texas, according to the U.S. Energy Information Administration, whereas in Iowa, wind power represents 58% of electricity generated.
Iowa and Kansas are two states where wind is the largest source of in-state power production, and in both states in 2019, wind surpassed coal as the top electricity generation source, according to the EIA.
The burning of fossil fuels such as coal contributes to climate change, and, according to the Iowa Department of Natural Resources, those changes have already included increased precipitation and precipitation extremes in Iowa, as well as increased humidity in the state, especially in the summer.
If that increase in moisture in Iowa’s air were to combine with the state’s winter temperatures – even if those temperatures, on the average, continue to increase – that could, in theory, cause more problems with glaze icing on blades.
“I don’t know what’s going to happen,” Hu said of what Iowa’s future may hold when it comes to whether ice may become more of a problem for its wind turbines.
What he does know is glaze icing conditions in the U.S. are currently more typical of the East Coast.
Hu also described how the wear of the stresses icing causes can reduce the lifetime of a wind turbine’s internal parts by three-quarters or more – so, he’s going to continue to study effective ways to de-ice blades.
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