Heat wave pushes power grid to the limit

VERMONT — Soaring temperatures swept across New England last week scorching Addison County, Vermont and the entire six-state region.
While thermometers were reporting temperatures way above normal, other meters also gave unusually high readings: Electricity demand in the region was just shy of record.
A heat wave, defined by the National Weather Service as a three-day period of temperatures above 90 degrees, slammed the county, with Middlebury reaching highs of 97 degrees on Thursday, July 21; 96 on Friday, July 22; and 94 on Saturday, July 23. Burlington hit a record high on July 21 of 97 degrees, and humidity was well above average, resulting in sticky air and increased use of air conditioners.
Naturally, demand for power to run those air conditioners drove up overall electricity demand. The New England electricity grid hit several benchmarks for energy consumption.
“Friday, July 22, New England hit the second all-time peak for electricity use in the afternoon,” said Ellen Foley, director of corporate communications at ISO New England — the not-for-profit corporation that is the central hub for energy transactions across the six-states’ 350 power plants and related utilities.
“Our preliminary number indicates that we topped off at 27,762 megawatts,” she continued. “The all-time peak occurred back on Aug. 2, 2006, where we topped off at 28,130 megawatts.”
For reference, on a typical day one megawatt powers approximately 1,000 homes. So Friday’s production was enough to power approximately 27,762,000 homes on an average day, which is about twice the number in New England.
“Anytime we have a heat wave, you’ll see demand sustain itself and then grow day by day,” said Foley. “The demand grew every day (last week) Sunday through Friday.”
The increased demand sent ISO New England scrambling to reduce consumption, work with neighboring grids and dip into its safety reserve, which acts as a protective padding against overloads.
“We used everything that was available to us. We also took some precautionary steps on Friday … that included bringing in emergency power from our neighboring power grids in New York and elsewhere,” said Foley.
ISO New England also tries to lower energy usage by offering electric users, including Middlebury College, incentives for lowering their demand (see related story).
The source of this skyrocketing demand? Air Conditioning.
“From the late ’80s through the early ’90s, New England shifted from being a winter peaking system to a summer peaking system and that was due to the installment of air conditioning,” said Foley.
And Friday wasn’t the only near record-setting day for consumption.
Thursday’s 26,533 megawatts of demand cracked the ISO New England top 10 list, coming it at number 10, and Saturday’s 23,304 megawatts came in second all-time for weekend days. These numbers, Foley explained, are believed to be accurate but still need to be verified.
Dorothy Schnure, spokeswoman for Green Mountain Power, explained that the utility tried to cut its own power use during this period and that ISO New England called on GMP to bring extra power generators into use.
“We turned on our combustion turbine unit, which only runs a couple hundred hours a year. That ran for 13 hours (and) our diesel units ran,” she said. “One of the things that’s really notable is our Searsburg Wind Plant generated close to three megawatts throughout that period of time.”
But she also explained that when the grid nears peak capacity, more expensive and dirtier sources of power are fired up.
“When New England is hitting a peak load, what you have to do is turn on power plants that are the most expensive to operate … so during those peak periods, the most expensive and typically the dirtiest — highest emissions — sources are called on to run,” she said.
Central Vermont Public Service, Vermont’s largest utility, was also called on to provide more power to the grid.
“We brought on some extra generation at ISO New England’s request, but were not asked to do any load reductions or voltage reductions,”  spokesman Steve Costello said. “Our local loads were well below historic peaks.”
Reporter Andrew Stein is at [email protected].

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