Power grid put under stress over Christmas holiday

Oil became dominant fuel, reserve supplies came up short

A correction has been added to the story.

OVER THE CHRISTMAS holiday, the New England power grid relied heavily on oil to meet the region’s electricity needs and for a 2 ½-hour period on December 24 had to scramble to cover a temporary shortfall in power supplies.

The shortfall on the afternoon of December 24 came about because roughly 2,000 megawatts of power generation went offline and imports of electricity via a transmission line from Quebec declined by about 200 megawatts. (CORRECT’ION: An earlier version of this story incorrectly said the electricity that came in over the transmission line declined by 700 megawatts.)

Matt Kakley, a spokesman for the grid operator, ISO-New England, said the system fell short on operating reserves for about two hours and implemented emergency procedures to bring new generators online.

 “It was definitely a tense few hours,” Kakley said. “It was a hectic day, but the procedures we had in place worked as intended.”

Under the emergency procedures, new power generators came online and their costs will have to be paid by the generators who had promised via the wholesale markets to make their power available but for one reason or another were unable to do so.

One industry source said the penalties assessed on the generators who failed to deliver are likely to add up to millions of dollars.

The transmission line from Quebec is typically supplied by Hydro-Quebec, which is seeking to supply electricity to Massachusetts under a long-term contract. The Hydro-Quebec power is often described as “firm,” meaning it would be delivered around the clock 24 hours a day. The shortfall on December 24 was power that had been pledged the day before, but never arrived.

Kakley indicated the power promised to New England was most likely shifted for use within Quebec. “From what we understand, it was high demand up there,” Kakley said, referring to Quebec.

At the same time the power grid was struggling to meet demand, it also had to deal with a dramatic shift in its resource mix. Normally, natural gas is the dominant fuel used to generate electricity in New England and oil is rarely used. But from late morning on December 23 to the evening of December 28 the region relied heavily on oil to meet its power needs.

Kakley said oil-powered generation, which emits more greenhouse gases than natural gas, was used to meet 30 to 40 percent of the region’s power needs, more than any other fuel.

The peak usage came at 4:45 p.m. on December 24, when oil was used to generate 6,538 megawatts of electricity. A graphical depiction of the grid’s resource that afternoon had oil generating 41 percent of the region’s electricity, nuclear 25 percent, 15 percent natural gas, 9 percent hydro, 9 percent renewables, and less than 1 percent coal.

The morning of December 23 no oil was burned to produce electricity and by the evening of December 28 oil had largely disappeared from the region’s fuel mix.

Kakley said a cold snap over the Christmas holiday drove up the price of natural gas, so generators who run on oil or are capable of running using either oil or natural gas switched to oil to save money.