A deluge of rain in the Northwest is forcing hydropower turbines in the Columbia River system to work overtime. During the past few days, the 31 federally operated dams in the region have been running at full capacity—12,000 MW—generating 144% more than normal. The Bonneville Power Administration (BPA), asking regional utilities to back generation down, has been giving power away almost for free since Wednesday.

The federal agency said it is “pulling out all stops” to manage heavy runoff and protect the fish such as young salmon migrating downstream and many other species, some which are listed under the Endangered Species Act.

The issue is nitrogen saturation, which can give fish gas bubble disease, similar to the bends in human divers. “Too much water spilling over dams churns air into the water, increasing the proportion of nitrogen in the water. Northwest states have set limits on the level of nitrogen saturation allowed in the water to protect fish,” it said. “And BPA’s normal practice of reducing hydro generation to let wind generation exceed its schedules could increase the likelihood of exceeding those limits.”

BPA has already asked the Energy Northwest nuclear plant to back generation down to as little as possible, and it is selling power to Northwest and California utilities for very low prices—even giving power away in some hours to keep turbines turning and spill as low as possible.

According to the federal agency, the U.S. Army Corps of Engineers and Bureau of Reclamation are also holding back as much water as possible, and B.C. Hydro has reduced water flows coming down the Columbia from Canada.

Wind power, the new resource on the system, is doing its part. “Rain-laden storms also whip the wind through the Columbia River Gorge, causing extreme fluctuations in the output of the region’s wind power fleet, which, at full output, can now generate enough power for more than two cities the size of Seattle,” BPA said.

Normally, BPA backs off hydro generation when wind farms generate more power than wind project operators scheduled, up to certain limits. This week, BPA informed the region’s wind projects that it had limited flexibility to back off hydro generation to absorb excess wind power, because that would increase the likelihood of harming fish.

When BPA runs out of available reserves, it orders wind projects to "stick to schedule" plus available reserves, and to feather their blades (pitch the turbine blades so as to reduce their lift capacity as a method of shutting down the turbine during high wind speeds) if they start generating additional power during an hour.

"We just don’t have anyplace to store excess water that can be a result of the excess wind right now, without risking fish," said Steve Oliver, vice president of BPA Generation Asset Management. "We’ve been talking with the wind community about this possibility for a couple of years now, and discussed it last year in the course of setting rates for our balancing reserves. We appreciate their cooperation."

The next few days will be crucial, Oliver said. “Once this slug of water passes through the system, we should be back to normal—assuming we don’t get a sudden heat wave taking all the snowpack off at once or another string of storms.”

“But it’s ironic for all of us, especially in what is otherwise a dry year, that we have too much of two good things right now,” he concluded.

Source: BPA, POWERnews