As Electricity Demand Grows, Grid Manager Explains Operations
As heat and humidity motivate people around New England to switch on air conditioning systems, the electrical power grid will be burdened with increasing demand even as the weather itself creates stresses on the equipment used to produce and transmit power.
In the six-state region whose power is managed by Independent System Operator of New England, Massachusetts is by far the largest consumer, accounting for 46 percent of the power consumption with Connecticut accounting for the next highest amount with 26 percent usage.
ISO New England serves as the dispatcher for 32,000 megawatts of generating capacity carried on more than 8,000 miles of high voltage transmission lines throughout the region. A single megawatt can power about 1,000 homes, according to ISO New England. The region's all-time peak demand of 28,130 megawatts was in the midst of a heat wave on Aug. 2, 2006.
Over the weekend and into Monday, temperatures around the state exceeded 90 degrees with more of the same forecast for Tuesday, a phenomenon that when combined with high humidity leads to the greatest strain on the electrical grid.
While the power grid operated normally on Monday, ISO New England, a non-profit, has procedures set out for mitigating a major draw on the supply, including receiving power from Canada, where the demand is higher in the winter than the summer.
ISO New England spokeswoman Ellen Foley spoke Monday with the News Service about the situation.
WHAT DRIVES UP DEMAND?
"It's actually a combination of heat and humidity that will drive up consumer demand, and that's what we're seeing here in New England today. It began yesterday, and we expect it to continue through tomorrow. Yesterday we hit a peak load of 20,250 megawatts, and that's a pretty healthy peak for a weekend load. And today we expect to see the demand or load hit 25,000 megawatts. We expect to see that around 5 o'clock this afternoon, and so far the forecast is tracking with the actual demand, so we're right on target to hit that demand level later on this afternoon. And tomorrow, we are expecting similar weather conditions with temperatures in the 90s, low 90s, and also a very high dew point, a dew point over 60, and it's typically the humidity that drives up demand even more than the heat, but it's a combination of both. So tomorrow we're expecting a forecasted demand of 26,300 megawatts. Our all-time peak demand was recorded back in 2006 during a heat wave where we topped off at 28,130 megawatts. So we are seeing high demand on the system, but it's also something that we expect this time of year because of the heat and humidity."
EFFECT OF HEAT ON POWER SYSTEMS
"You have to remember that power plants or generators are large machines and they have equipment that can be subject to heat conditions. They can have tube leak for example, or different types of equipment failures. So they have to be very mindful of that in the heat, especially as you get into the second or third day of a heat wave. As a grid operator, we are aware of these types of issues that could crop up, and that's why in addition to meeting real-time demand, we have to for reliability purposes also maintain a reserve margin, or cushion of reserve. So in the event that a power plant or transition line trips off suddenly, we'll have – I'm going to use a baseball analogy here – we'll have a power plant sitting on the bench waiting to be called into the game, so that's what our reserve margins are."
SHIFT TO MORE AC
"Here in New England, we have changed from a winter-peaking system to a summer peaking system, and that has happened over the past two decades or so, and that is because of the prevalent use of air conditioning across the six New England states."
USUAL SUMMER DEMAND
"Summertime demand can really range. And we typically see it in the 20 to 22,000, 23,000-megawatt range, so the load on the system – load and consumer demand are the same thing – today's load of 25,000 megawatts is, I'd consider it a robust amount of consumer demand that we're seeing on the system, and if you connect the dots it goes right back to the heat and humidity and the use of air conditioning."
PROCEDURES DURING PEAK DEMAND
“We are operating under normal conditions, so that means that we have enough supplies to meet demands, and also maintain that reserve margin, or that cushion of reserve. So say, for example, we lose transmission lines or we lose power plants, or we lose a combination of both. We have operating procedures in place that we can call upon that will help us balance supply and demand in real time during those tight system conditions. We are operating under normal conditions today, so we have not called any of those steps or those procedures today, but those steps could include for example, bringing in emergency imports from our neighboring power systems in Canada or from New York. It could also include calling on demand response … Demand response is customers that are aggregated that when they get the signal they reduce their electricity use, so instead of increasing demand, they’re reducing the demand on the system … It really depends on the type of customer that they are, whether or not they reduce their use or whether they use their own on-site generation… In extenuating circumstances we can call upon the public to conserve electricity. We have not done that recently, but we do have steps in our procedures to call for that.”
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