Northwest wind farms can be big on energy, low on peak capacity

Wind power's intermittency as an energy resource but minimal contributions toward peak-capacity needs are further evidenced in operational data from three Washington and Montana wind farms. Monthly and even daily energy production vary substantially.

Officials from NorthWestern Energy and Puget Sound Energy recently shared these and other wind-power experiences, including reserve requirements (challenging) and wind forecasting (improving). These tales come from the 135 MW-capacity Judith Gap wind farm in central Montana, whose entire output NorthWestern buys from developer Invenergy Wind, and PSE's 150 MW-capacity Hopkins Ridge and 229 MW-capacity Wild Horse wind projects in southeastern and central Washington, respectively.

NorthWestern's wind portfolio totals 149 MW capacity and provides 9 percent of the investor-owned utility's energy supply, Energy Supply Planning Director Dave Fine told the Northwest Power and Conservation Council July 15 in Kalispell, Mont. He said the dual-peaking utility has an average load of 725 MW, dropping as low as 400 MW and peaking around 1,200 MW.

Judith Gap power also is a bargain for NorthWestern, at about 3.2 cents/kWh, according to Chief Supply Officer John Hines.

However, Hines said wind power provides virtually none of NorthWestern's capacity requirements, and the utility needs on-call contracts and other means to ensure it meets load.

"The relationship between load and wind output is almost zero," the former council member told the current council. "That's a real issue for us. We continue to learn almost every day some things about wind operations on our system."

Fine said Judith Gap's capacity factor annually averages about 40 percent, in line with projections before the wind farm started commercial operations in February 2006. But that average masks large variations. In January 2007, Judith Gap recorded a "phenomenal" 68 percent capacity factor, Fine said. But in July 2007, the capacity factor dipped to 18 percent. Other 2007 monthly capacity factors ranged from 24 percent to 63 percent. "There's a real dichotomy in terms of capacity factor, and a great deal of seasonality associated with that resource," he told the council.

Fine also shared data from Jan. 10, 2006, when Judith Gap cranked out 1,564 MWh and an average of 65 MW. However, "the vast majority" of times during the period, the 90-turbine facility generated much more or less than 65 MW-a production graph of that day features sharp peaks and valleys-and the varying output accounted for utility load percentages ranging from around zero to nearly 20 percent. "On any given day, the wind production profile can change dramatically," Fine said.

NorthWestern relies on "a very elaborate and proprietary system" for wind forecasting, Fine said. "On any given day, the forecast can be right on the money, or we can miss the mark." When the latter occurs and NorthWestern becomes long or short on resources, "there's usually a financial consequence to ratepayers," said Hines.

NorthWestern officials also discussed challenges associated with regulating reserves for wind power. Hines said they initially thought Judith Gap's 135 MW would require 15 MW of such reserves. But the figure eventually turned out to be 25 MW, or 18 percent of wind capacity, costing almost $1.8 million-and climbing as other utilities retain reserves for their own system needs, as Idaho Power has done in no longer providing NorthWestern a portion of its reserves, Hines noted. The Montana utility has no regulating reserves or owned resources, although it has dispatch (but not reserve) capabilities from the 54 MW Basin Creek natural gas plant, according to Fine.

Puget Sound Energy also has found "an illiquid reserve market" in the region, PSE Energy Supply and Planning Director David Mills told California Energy Markets. He thinks this could pose problems as more wind power enters the system, but he hopes solutions will emerge. This topic was flagged in the Northwest Wind Integration Action Plan.

Puget recently announced Hopkins Ridge and Wild Horse both have surpassed 1 million MWh of generation since they started operating in 2005 and 2006, respectively. "This year, both facilities are producing about 6 percent more electricity than our meteorological and engineering studies had predicted, and have shown themselves to be reliable resources throughout the year," said PSE Chief Resource Officer Kimberly Harris in a news release.

Mills said Hopkins Ridge operated at 45 percent capacity factor in March and April, while Wild Horse came in at 42 percent for April. Given this year's delayed runoff, the robust spring wind power was "sort of a blessing," he said. In December 2007, Hopkins Ridge ran at a 43 percent capacity factor, while Wild Horse checked in at 36 percent. Mills said Puget remains a winter-peaking system, with a 5,000 MW peak in the cold months compared to slightly more than 3,000 MW in summer.

Overall capacity factors for both wind projects are a bit above 30 percent, Mills said.

He also noted PSE's wind output is "not coincident with peak," which makes meteorological sense. Puget peak loads in both winter and summer tend to occur when high-pressure systems hover over its service territory and winds are generally calm. Mills believes this situation will improve with more geographic diversity of wind farms distant from load centers-a point also emphasized in the Northwest Wind Integration Action Plan.

Mills also has observed improvements in the sophistication and accuracy of wind forecasting.

Wind energy and capacity values are also addressed by the Pacific Northwest Resource Adequacy Forum. It assumes 30 percent of nameplate capacity for wind's energy production, based on historic performance of regional wind farms. And as a placeholder, the forum assigns wind a 5 percent capacity value over a sustained 18-hour peak period. That reflects data analysis from wind projects in the Bonneville Power Administration's control area, according to planning council senior power systems analyst John Fazio.

Wind advocates argue wind fundamentally should be viewed as an energy resource. "When the fuel is free, why not use that?" asked Rachel Shimshak, director of Renewable Northwest Project. "I think people should think of wind more like load. It comes and goes, and . . . the system responds." Utilities have to meet peak demands regardless, through demand- and supply-side strategies, and "that's an expensive thing to meet no matter how you slice it."

Randall Swisher, executive director of the American Wind Energy Association, told CEM, "You take the wind when it's blowing and rely on other resources when it is not. It isn't a particular challenge for utilities today to integrate 10, 20 percent of their energy from a variable resource like wind, any more than it is to manage the variability on the load side." He added that absorbing intermittent generation can be an issue for small utilities or systems, but not for large regional markets [Mark Ohrenschall].