People wait in line to fill propane tanks Wednesday, Feb. 17, 2021, in Houston. Customers waited over an hour in the freezing rain to fill their tanks. Credit: David J. Phillip / AP

New England’s historic overreliance on fossil fuels to power its electricity grid may come to a head this winter in the form of rolling power outages if a prolonged cold spell hits, the grid operator said Monday.

ISO New England has warned about the potential effects of the region’s heavy use of natural gas to power its electricity for at least a couple decades. But its wording this year took a stronger tone in the face of the supply shortages and natural gas prices that have soared almost 95 percent from October 2020 through October 2021.

In a worst-case scenario, ISO New England might have to institute region-wide rolling power outages that would affect different people at different and short periods of time, Gordon van Welie, ISO New England’s president and CEO, said. He said he doesn’t want to cause undue alarm, but it makes sense to examine potential threats now.

There have been no grid-wide rolling outages in New England to date, but if they are required this winter, ISO New England would give each utility in the region a percentage by which to lower electricity supply, said ISO New England spokesperson Matt Kakley. The grid operator would inform consumers of any outages via news outlets and its website.

“But I’m quite confident that ISO New England is evaluating every single potential option to avoid having this occur,” Andrew Landry, acting Maine public advocate, said.

The region is in a more precarious state entering this winter because there also are supply shortages of heating oil and liquefied natural gas, both of which can be used to power the grid when there isn’t enough natural gas. Those fuels filled the natural gas gap during the 2017-18 cold snap and the cold winter in 2013-14, so controlled power outages were not necessary, ISO New England said.

But this year, the world’s liquefied natural gas market is much tighter than it was last year, with Asia and Europe competing for supplies. Shortages of truck drivers are causing logistics logjams with oil. Maine and other New England states could come up short.

“The region would be in a precarious position if an extended cold snap were to develop and these fuels were not available,” van Welie said.

With early planning, van Welie hopes to avoid the widespread blackouts that hit Texas in February. That state saw a surge in demand for electricity to heat homes following a historic snowfall and unusual single-digit temperatures.

Mainers will see that price surge in their electricity bills starting Jan. 1. State regulators recently approved more than 80 percent rate hikes for standard offer electricity, the default rate for those who do not buy electricity from a third party. For Central Maine Power and Versant Power customers, that means an average $30 a month extra.

Even though this winter is projected to be warmer than average in New England, according to the National Oceanic and Atmospheric Administration, that does not eliminate problems from prolonged stretches of cold weather.

Maine Gov. Janet Mills’ energy office said it and the regulatory Maine Public Utilities Commission are in regular contact with ISO New England to closely monitor energy trends.

ISO New England estimates that the peak electricity use in the region this winter will be 19,710 megawatts under normal weather conditions. That could rise to 20,349 megawatts during below average conditions. Last winter’s peak demand was 18,756 megawatts on Dec. 17, 2020. The record high was 22,818 megawatts set on Jan. 15, 2004, during a cold snap.