Utility customers gulped power at record levels Monday and Tuesday as the Portland area entered the longest stretch of 100-degree days in nearly three decades.

Portland General Electric Co. reported scattered blackouts in the metro area as transformers overheated and sagging power lines came into contact with foliage, and in one case, a passing beer truck. But both utilities, as well as the big kahuna of regional power sales -- the Bonneville Power Administration -- said they have adequate juice on tap to slake the region's electricity thirst.

Thank the recession and California for that. The former knocked out a good chunk of industrial demand for electricity, while the latter is experiencing relatively cool temperatures and moderate power use.

In combination, that puts less pressure on the region's wholesale power markets, so when utilities go to purchase electricity, they can find what they need at a reasonable price.

"You never say never, but at present, things are looking fine," said PGE spokesman Steve Corson. "The market is fluid, with power available."

It'll get worse

Demand is expected to gather more steam today. The excessive heat warning that the National Weather Service issued Monday lasts until 10 p.m. Thursday, and high temperatures aren't expected to dip below 90 until Monday.

Heat waves have a cumulative effect on the electrical grid, and an unusual aspect of this broiler is exceptionally high night temperatures. Buildings aren't cooling down, so air conditioners are forced to work harder. That puts more strain on transmission equipment, which has less chance to dissipate heat.

"The longer it lasts, the more concerned we get because it puts more strain on the system and presents more opportunity for something to go down or trip off," said Michael Milstein, spokesman for the BPA.

The public utility customers of the BPA, which sells power from 31 dams and a nuclear plant in the Columbia River basin, set a summer demand record Monday and Tuesday and will likely top those levels today, Milstein said. The agency's overall load, including power being sent out of region, is still about 15 percent short of the record it hit in August 2006, and well within its generation capacity.

PGE and PacifiCorp also experienced record summertime demand. PGE customers' peak demand of 3,910 megawatts Tuesday was still 4 percent short of the utility's all-time peak of 4,073 megawatts on Dec. 21, 1998. But rising summer temperatures and the growing prevalence of air conditioning in the Northwest mean that demand, which historically peaks in winter, is now growing fastest in the summer. PGE says that about 72 percent of its customers have air conditioning today, versus only 30 percent in 1990.

Summer is also when electricity is typically in shortest supply because of lower water flows and California's demand. On hot days, the Northwest can run short, as it did during an unexpectedly scorching stretch of days in August 2006 when PGE was forced to declare its first ever "power emergency." That was a perfect storm that combined a heat wave in California with the crash of one of PGE's power plants. But higher summer demand is becoming a way of life.

Long-term concerns

In many ways, this is not an ideal time for a heat wave.

Last winter's low snowpack means that river flows are at 83 percent of normal, diminishing hydroelectric capacity as dam operators maintain sufficient water flows for fish passage. Both of PGE's coal-fired power plants, normally the backbone of its generation fleet, are off line for extended maintenance outages. And the high pressure system sitting over Oregon and Washington has becalmed the legions of wind turbines that now line the eastern end of the Columbia River Gorge.

While utilities say those factors are unlikely to create a crisis this time, they underscore longer-term concerns about the impacts of regional population growth, climate change, greenhouse gas limits and an increasing reliance on intermittent sources of power like wind.

The region is expected to add 3.6 million residents between now and 2030, according to the Northwest Power and Conservation Council. And summer power demand is expected to grow 1.4 percent a year, outstripping winter growth of 1 percent.

Supply is another story.

Hydropower accounts for about 40 percent of the region's electricity, and global warming could have a significant impact on river flows. The consensus among scientists is that climate change will cause more of the Northwest's precipitation to fall in the form of rain versus snow. A lesser snowpack means a smaller bank of stored water, and an earlier spring runoff, when the resulting hydropower is less valuable.

Greenhouse gas limits may also force utilities to close some of their coal-fired power plants, which provide a cheap and reliable source of power year round. Meanwhile, utilities are investing heavily in renewable resources such as wind to meet state mandates. But they can't count on that power when they need it most, as the same high-pressure systems that create heat waves tend to come with low wind.

"There seems to be a lot of evidence that when you get extreme cold or heat events, you don't see very much wind generation, at least at the east end of the gorge," said Wallace Gibson, a generation and transmission analyst with the power planning council. "Right now, we're pretty much not relying on wind to meet peak loads."

Ted Sickinger: 503-221-8505; tedsickinger@news.oregonian.com

