Wind power and developments outside the Northwest are changing the character of the region's electricity system. However, the power supply will remain adequate during the next five years with the addition of new generation and additional energy efficiency equal to the output of a single, medium-sized power plant.

Those are among the findings of ananalysisby the Portland-basedNorthwest Resource Adequacy Forum.

"As the region's power system has evolved over time, it's become much more dynamic and complex, and the need for comprehensive and timely information has become critical," says Rhonda Whiting, chairwoman of the Northwest Power and Conservation Council.

Adequacy is measured by the risk that power resources won't meet electricity loads. The council has set a maximum limit on that probability of 5 percent.

The forum's analysis shows that for 2017, the probability would be 6.6 percent if the region relies only on existing generating plants and new energy-efficiency savings outlined in the Council's Northwest Power Plan, which dates to 2010. However, the analysis suggests that a number of actions by utilities—new generation, new energy efficiency, or a combination—would bring adequacy to the minimum acceptable level by 2017.

What's important is that the result is 350 megawatts of new capacity at times of peak load, according to the forum. Demand response, in which customers agree to reduce their consumption during periods of high use, also may be an option but wasn't included in the analysis.

Historically, planning for new power supplies was driven by anticipated annual deficits. Now the focus is shifting to ensure that the power supply is adequate to meet winter and summer peaks in demand—particularly winter peaks.