(Bloomberg) -- The risk of power failures this summer remains elevated for many parts of North America amid soaring demand and generator shutdowns. 

The main Texas grid is especially vulnerable at sunset when solar generation plunges and demand remains high, with the riskiest hour from 8 to 9 p.m. in August, the North American Electric Reliability Corp. said in its summer assessment Wednesday. There’s an 18% probability a grid emergency will be declared and a nearly 15% chance for controlled blackouts in that period.

Grids across the US are struggling to provide reliable power amid rapid growth in electricity demand and extreme weather. Recent summers in Texas have revealed vulnerability at dusk as reserves fall to low levels and set off a series of events to keep the lights on, including rolling blackouts. 

Read More: Texas Grid Issues Alert for Potential Power Emergency

Electricity consumption in Texas set records nearly two dozen times in the previous two summers. Separately on Wednesday, the state’s grid issued its fourth warning of a potential evening supply shortfall in about a month. 

In addition to the outlook in Texas, NERC said New England faces tight supplies during extreme weather after a 1,400-megawatt Mystic Generating Station was shut this month. Regional grids operating in the Midwest and Southwest also are at risk of power shortfalls, along with British Columbia and Saskatchewan in Canada. 

“A large amount of North America could be at risk of supply shortfalls during heat waves and extreme summer conditions,” Mark Olson, manager of reliability assessment, said during a media briefing.

While stress persists in heavily populated areas, NERC’s summer outlook was less dire than last year because of plentiful hydroelectric generation in the West, a lot more solar power and reduced wildfire risk. 

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