Soaring temperatures have led to scattered power outages for thousands of New Hampshire residents this week. Still, utility managers say the electric system is handling the heat wave relatively well.
In high temperatures, widespread use of air conditioners, fans and other appliances can overload infrastructure that keep the lights on.
It can lead to partial power – those periods when the lights dim or air conditioners sputter – or complete outages. That's not to be confused with brownouts, where there isn’t enough power supply in the system to meet demand and some residents lose electricity.
That hasn't happened this week, but Eversource says heat-related equipment problems knocked out power for more than 4,000 people Tuesday. And Unitil spokeswoman Carol Valianti says two of their transformers overloaded from demand.
“In an extreme situation, when you have that much demand on the system, it can lead to that,” Valianti says.
She says utilities have to rely on good demand forecasts and toughened infrastructure to get through periods like this safely.
"We do maintenance to see if there are any weak points in the system, and we do it really throughout the whole year,” she says. “So generally speaking, the system holds up well in extreme conditions like this.”
Liberty Utilities and the New Hampshire Electric Cooperative say they didn’t have any heat-related issues this week. But peak demand can mean high rates.
The region's electricity price per megawatt-hour topped $300 on Thursday afternoon – well above average. There was also more coal in the region’s fuel mix than usual, signaling a need for the kind of reserves used in times of high usage.
Peak demand this week has been around 24,000 megawatts, below New England’s recent record of 28,000 on a July day in 2006. Other power outages this week – including one affecting about 1,300 Unitil customers in Concord on July 4 – were caused by fallen tree limbs, squirrels and birds.