Better forecasts put more wind on grid

Posted Nov. 11, 2011, at 8:57 p.m.

MINNEAPOLIS — Using new weather-forecasting technology, Xcel Energy says it has vastly improved its ability to predict when wind turbines will run and boosted how much electricity they send to the power grid.

The new capability saved $6 million last year by allowing the utility to avoid running fossil-fuel power plants when it could rely on wind power instead, according to the Minneapolis-based utility.

Scientists at two national labs in Boulder, Colo., contributed to the new prediction system, which was developed under contract to Xcel and used by the utility over the past two years. It was formally turned over to Xcel last month.

The system feeds real-time data from the National Weather Service and wind-farm sensors into software that forecasts wind turbines’ power output, primarily for the next day.

William Mahoney, program director at the National Center for Atmospheric Research, the prime developer of the system, said it is 35 percent more accurate than previous prediction tools, and builds on decades of atmospheric research by scientists at the Boulder lab, a unit of the National Science Foundation.

“We certainly took advantage of their knowledge base, technologies that have been developed, software and other things and … brought it to bear on this solution,” he said.

John Welch, director of power operations for Xcel in Denver, said the technology is helping energy traders and dispatchers there to better predict the output of the utility’s wind farms in Minnesota, Wisconsin, Colorado, New Mexico and Texas.

Each day, Xcel must predict how much wind power will flow onto the grid for the next day, and decide how much to rely on coal- or natural gas-fired power plants. If wind farms generate more than predicted — sending too much juice to the grid — their output typically is curtailed by turning off some units and by other means. Big power plants can be harder to dial back.

These energy-wasting wind farm curtailments had been happening about 2 percent of the time. Xcel says the new prediction system has cut that to about 1 percent.

Xcel, which has the most wind power capacity of any U.S. utility, also said it is hitting new milestones in generating off-peak wind power in Colorado and Minnesota, mainly at night when wind blows and electrical demand is low.

In Colorado, after two new wind farms were added, Xcel said it recently generated more than 50 percent of its nighttime load from wind on eight occasions. In its Minnesota region, the utility said it recently hit a 37 percent wind power share at night.

“Five years ago I never would never have anticipated that, but it is a new reality and one that is exciting. We’re glad that we’re on the leading edge of this,” said Welch, who attributed those milestones partly to better forecasting.

Michael Goggin , manager of transmission policy for the American Wind Energy Association, an industry trade group, said Texas wind farms have contributed more than 25 percent of nighttime power, and utilities in Spain and Ireland have gotten 50 percent of off-peak electricity from wind.

Goggin said that as wind power supplies more electricity, “we need to be doing the right types of forecasting. … It pays tremendous dividends, as the Xcel numbers point out.”

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