That balance began to shift over the last few years as entrepreneurs built hundreds of wind machines nearby in the Columbia River Gorge, an area that utility executives now call a “wind ghetto.” While the wind turbines produce electricity far below their capacity most hours of the year, they get busy when a storm rolls through, which is when river flows are highest, too.

The agency can simply shut down the wind machines, and it did so intermittently this summer when excess power threatened the grid. But that angered the wind operators, who earn money from the electricity they sell and from tax and other credits based on their production.

This June, several wind companies appealed Bonneville’s policy to the Federal Energy Regulatory Commission, calling it discriminatory, and in August they filed a federal court challenge that is still pending.

For Bonneville, the full dangers of excess supply first hit home during the June 2010 emergency, when a severe storm whipped through the region. The transmission network had so much power that the agency turned off all its fossil fuel generation, gave electricity away to neighboring networks and even told the system’s only nuclear plant to slash its production by 78 percent, a highly unusual step.

The region squeaked through, but the agency was stretching its resources “to their limits,” said Doug Johnson, a spokesman for Bonneville. At one point the system was running almost entirely on renewable energy.

“This is probably about the only place in the country where that could happen,” said Michael Milstein, another spokesman with the agency.