Knowing Which Way the Wind Blows

“You don’t need a weather man to know which way the wind blows,” Bob Dylan once sang. But if you’re a wind farm developer, you absolutely do need someone to help you know not only which way the wind blows, but also where, when, how often, and for how long. That’s where wind energy forecasting comes in.

“The knock against wind has always been that it can’t provide consistent, high-grade power because it’s unpredictable and intermittent,” says Kristin Larson, manager of wind energy forecasting at Seattle-based 3TIER, a renewable energy “information-to-decision” company that provides developers with data on wind, solar, and hydropower resources. “But with wind energy forecasting we remove a lot of that uncertainty by using sophisticated tools to predict how much wind there will be in a given location over time.”

Like most wind forecasting companies, 3TIER compares short-term wind data at a potential wind farm site with long-term measurements going back as much as 50 years. (Much of the long-term information comes from weather balloons, satellites, and surface observations at airports around the world.) Using powerful computers to crunch the numbers, wind forecasters can provide an accurate portrait of a site’s wind resources, past, present, and future.

What really matters for wind farm developers (and their potential sources of funding), though, is the degree of accuracy with which forecasters can predict how the wind blows. Wind is notoriously sensitive to changes in temperature, terrain, humidity, and other factors. Even a relatively small change in elevation from one location to another can result in significant differences in wind speed. For example, as a recent article in The Economist noted, a 2009 study by the National Renewable Energy Laboratory (NREL) found that an elevation difference of only 50 meters caused changed average wind speed by 2.5 mph–enough of a variation to affect as much as 15 percent of a wind farm’s power output.

So wind forecasters strive to be as accurate as possible by designing computer models that take into account not only past and present weather and topography data but also possible future changes. “Wind developers need to know not just what the wind is doing now but what it will do in the future,” says 3TIER’s Larson. “That depends on climate change, tree growth or loss of trees, land development and lots of other factors.”

In other words, wind forecasting is a tricky, difficult business. 3TIER specializes in numerical weather prediction (NWP)–a common technique that creates a 3-D grid model of the atmosphere and plugging in temperature, humidity, and air pressure data from a proposed wind farm location to simulate wind speed. Wind developers use that information to calculate how much power their turbines will generate over time.

Wind forecasting has been around in one form or another since the late 19th century, when Danish wind power pioneer Poul la Cour did some of the earliest scientific studies of the relationship between wind, land, and climate. Today’s forecasting technology is a big leap forward and will continue to improve, Larson predicts, as wind power continues to grow. “The technology is already pretty mature, it’s just not used as widely as it could be,” she says. “But as more wind power comes online and feeds into the grid, operators will come to see the value of better and more accurate wind predictions.”

Visit renewablebook.com to read more of Jeremy Shere's writing on renewable energy.