Large-Scale Wind Farms Cut Turbine Efficiency: StudyJohn Simpson | November 30, 2016
A new study by researchers from the Max Planck Institute for Biogeochemistry has yielded lowered expectations of wind energy potential when deployed on a large scale.
The scientists, led by postdoctoral researcher Dr. Lee Miller, hypothesized that, because every turbine removes energy from the wind, many turbines operating on a large scale should reduce overall wind speeds. With many turbines, this effect should extend beyond the immediate wake behind each turbine and result in a general reduction of wind speeds, they reasoned.
To simulate the effect that many wind turbines have on wind speeds, the researchers relied on a global climate model commonly used in atmospheric research rather than local wind speed observations. They performed a range of scenarios to determine the maximum wind energy potential in specific regions on every continent.
"Wind speeds in climate models may not be completely realistic," says Miller. "But climate models can simulate the effect that many wind turbines have on wind speeds, while observations cannot capture their effect."
The researchers determined that only 3%-4% of land areas have the potential to generate more than 1.0 watt of electricity per square meter of land surface, with a more typical potential of about 0.5 watt per square meter or less. These estimates are similar to previous climate model studies but about 10 times lower than estimates based on observed wind speeds.
According to the researchers, this strong discrepancy can be explained by the 40%-50% reduction of wind speeds in climate model simulations. As wind speeds disproportionally affect the electricity generation of wind turbines, the lower wind speeds result in much lower wind energy potential obtained by climate models.
They calculated that, when wind energy is used at its maximum potential in a given region, each turbine in the presence of many other turbines generates, on average, only about 20% of the electricity compared to what an isolated turbine would generate. The researchers plan to look into observations of present-day wind farms to see whether this effect can already be seen.
This finding would imply that, in order to maintain today's high turbine efficiencies and favorable economics, the future expansion of wind energy should proceed with much greater spacing between turbines than what is common to wind farms of today.