Wind giveth, but power plants may be taking away

Wind energy is seen as a vital piece of the renewable-energy movement.

But it may be contributing to the pollution problem along the Front Range, according to a draft report sponsored by members of Colorado’s natural gas industry.

The report says that the greatly increased use of wind energy in the past few years may have raised pollution levels from some coal-fueled power plants owned by Xcel Energy Inc. That’s because the frequent change in output asked of power plants, in response to the availability of wind and solar power, adds to pollution, the report says.

If the report’s conclusions are true, then that challenges beliefs about the connection between renewable wind power and improved air quality.

But representatives of environmental groups and Xcel say they have doubts about its methods and are skeptical about its conclusions. The final report is expected to be completed within weeks.

“We have some questions,” said Roy Palmer, Xcel’s director of state government affairs.

“We think this study has some very serious flaws and doesn’t consider the overall air pollution and public health benefits on an annual or seasonal basis,” said Vickie Patton, the Boulder-based deputy general counsel for the Environmental Defense Fund who works on clean-air programs for the advocacy group.

Conventional wisdom says the use of renewable resources, such as wind or solar, to generate electricity cuts pollution levels and improves air quality because they don’t use coal or natural gas to generate power. Fossil fuels have pollutants, such as mercury, sulphur dioxide (SOx), nitrogen oxide (NOx) and carbon dioxide (C02), that are released when the coal or natural gas is burned for heat, which generates the steam needed to turn a turbine and make electricity.

At the end of 2009, Colorado’s wind farms were capable of generating as much as 1,241 megawatts of renewable energy, up nearly 3,800 percent since 2000, according to Interwest Energy Alliance, a Conifer-based trade group for wind power companies in the Rocky Mountains.

But when there’s no wind or sun, conventional power plants that use coal or natural gas supply the energy grid.

In Colorado, the wind typically blows the best — for power-generating purposes — at night, when demand for power is low and has traditionally been met by coal-fired power plants. Through the years, the state has added much more wind power, made necessary due to state laws mandating Xcel get 20 percent of its power supply from renewable resources by 2020. Gov. Bill Ritter is scheduled to sign a bill March 22 that raises that goal to 30 percent by 2020.

But the new report concludes that emissions levels at some coal power plants have increased because they’re throttled up and down to accommodate the fickle nature of renewable energy — particularly the wind, according to the Independent Petroleum Association of the Mountain States (IPAMS), which paid for the report, and Evergreen’s Bentek Energy Inc., which prepared it.

The study found that power output by coal-fired power plants fluctuated as much as 20 percent hour to hour, said Porter Bennett, Bentek president.

The impact on emissions, according to the study, are higher levels ranging between 2 million or 3 million pounds of SOx and NOx, to as much as 10 million pounds of increased emissions, when a power plant is throttled up, Bennett said.

“It’s like running your car in fifth gear, and then slowing to five miles per hour and then trying to speed back up again,” said Marc Smith, executive director of IPAMS. “Coal plants are meant to run only in fifth gear.”

Xcel spokesman Mark Stutz said via email that the utility’s first choice is to throttle back natural gas-fueled power plants, which are better designed to handle quick changes in operations, when the wind picks up. But the utility sometimes is “forced” to cut back coal plants’ output also in response to wind energy — and when it does, Xcel tries to minimize the impact on the plant’s operations and emissions, he said.

The increased emissions stem from two main factors, according to IPAMS and Bentek:

• Inefficiencies occur as power plants are ramped up and down.

• Rapidly increasing plants’ power output — particularly big, coal-fired ones — throws off the operation of air-quality control equipment meant to capture emissions, Bennett said.

It’s like a sudden blast of air tearing a hole in a net. The net still works in some areas, but more emissions get through until the hole is repaired, he said.

It can take up to 20 hours to recalibrate the control equipment, Smith said.

A recent presentation about the draft report was attended by representatives of Xcel; Western Resource Advocates (WRA), a Boulder-based environmental advocacy group that focuses on power issues; and the Environmental Defense Fund, a national advocacy group based in New York City. All three said they plan to study the final report when it’s complete.

“Analyzing system operations is very complex and isolating one specific activity, such as the impact of high wind events on coal operations, in comparison to the operation of the entire generation fleet in Colorado, is even more complex,” Stutz said.

Xcel’s emissions of NOx, and all emissions from Xcel’s fossil-fuel power plants, have dropped nearly 9,000 tons, or about 25 percent, since 2007 due to equipment upgrades that capture more emissions before they leave the plant, Stutz said.

Bennett agreed, but said the upgrades and overall drop in emissions mask increases at some of Xcel’s power plants.

John Nielsen, director of WRA’s energy program, said he thought there were two “serious flaws” in the draft study:

• The analysis didn’t include operations and emissions at power plants that supply power to Xcel, and its customers, in Colorado, but which aren’t owned by Xcel.

• Power plants might be ramped up and down due to a number of issues — such as maintenance at the individual plant or another plant, congestion on transmission lines or other reasons. Also, extrapolating the impact of a few windy days across an entire year could throw off conclusions, he said.

Information in the report came from utilities’ filings with the U.S. Environmental Protection Agency about the hourly emissions and operations of individual power plants.

Wind giveth, but power plants may be taking away

Denver Business Journal - by Cathy Proctor