(Inside Science) -- Numerous factors influence how much power wind turbines generate. For starters, the wind changes speeds and the arrangement of turbines affects how each one interacts with the wind and how much power each generates.
This week, at the annual meeting of the American Geophysical Union in San Francisco, researchers described how much of an effect they believe the crops planted below the turbines matter, too. Corn, a tall crop, slows down the wind more than soybeans, which are shorter. There could be as much as a three percent difference in wind speed at the height of the turbines, and a 14 percent jump in wind power generation, said Brian Vanderwende, a graduate student in atmospheric science at the University of Colorado Boulder.
The research looked at the difference in wind power generation in Iowa over an array of wind turbines that were arranged in an 11-by-11 grid composed of 121 turbines, which generally produces about 250 megawatts of electricity. Iowa ranks third among U.S. states in wind power generation, with more than 3,000 turbines currently in use.
Corn is tall, about eight feet tall by midsummer in Iowa. Together, its height and the pattern in which it's planted create a relatively large amount of roughness, a measurement that describes how much drag the ground imparts on the wind, slowing it down.
Soybean plants, another high-value crop grown in Iowa, are usually about half the size of corn. They generate a lesser amount of roughness, and therefore less drag to slow down the wind.
There are numerous other factors involved in optimizing wind power generation, such as the actual change in wind speed caused by the turbines, but the crops beneath the turbines are still a significant factor, said Vanderwynde.
"Looking at relatively simple ways to increase the power is a good idea," he said.
The researchers' model examined the effect in August, when plants are tall and mature. Earlier in the growing season the difference is less. After the harvest, the effect disappears.
Vanderwende said that there are numerous factors that can influence what a farmer plants, such as the effect turbines have on evaporation and moisture levels.
"I think it would be great to see more combined stakeholding between farmers and wind farmers," he said. This would allow decision makers to take a comprehensive look at the factors involved when making choices about what to grow.
"For this to work, you would have to have a combined incentive for the farmer and wind power operator," said Vanderwende.
Mark Jacobson, an atmospheric scientist at Stanford University in California, said that the research could help farmers make a thorough cost-benefit analysis before deciding what to plant.
"All that information helps people make better decisions," he said.
He noted that even if farmers didn't switch to soybeans, a slightly lesser wind speed would still generate good amounts of power. There are also other strategies that can be used to get more out of wind power, he said, such as using it to chill water at night, when electricity needs are relatively low, and using that for cooling the next day.