A lengthy, blistering heat wave that is blanketing the eastern half of the United States is putting significant stress on the nation's power grid as homeowners and businesses crank up their air conditioners.
Utilities say they're ready for high power demand and widespread electricity shortages or outages are unlikely. Lines and equipment are not fully taxed and there is more generating and transmission capacity available than usual because of the weak economy. Also, not many major storms are in the forecast, meaning fewer downed power lines.
The heat wave began a week ago in the Plains states and is expected to spread east through the weekend. It is lasting longer than most heat waves and is spread over an unusually wide area, according to Travis Hartman, the Energy Weather Manager at MDA Earthstat, which proves forecasts for utilities and other weather-dependent businesses.
Hartman predicts 90- to 100-degree weather from Chicago to Boston from Wednesday through the weekend. The Midwest is expected to see peak heat on Thursday while thermometers in eastern states will top out on Friday and Saturday. Philadelphia may break a 1957 record of 100 degrees on Friday, while Washington, D.C., is expected to reach 103, tying a record from 1926.
Texas and the southern Plains states will extend a long streak of hot weather. On Wednesday Oklahoma was expected to suffer its 30th day of triple-digit temperatures this year.
Nationwide, Thursday and Friday will be hotter than any time since 1950, says Hartman. "It's going to mean elevated power demand for an extended period of time for a lot of people," he says.
To meet demand, utilities are firing up special power plants used only a few days a year, delaying scheduled maintenance in order to keep all equipment on line and testing heat-sensitive switches and other equipment with high-tech devices like thermographers that can gauge temperatures to one-tenth of a degree.
"These are the days everyone wants to have their ACs on, their computers going while they watch TV," says Jon Jipping, Chief Operating Officer of ITC Holdings Corp., a transmission grid operator that owns grids in Iowa, Michigan and four other Midwest states. "These are the days we get ready for."
Peak demand for most utilities usually happens on a late weekday afternoon in mid-summer. That's when businesses are still open but people return home, turn on their air conditioners, lights and televisions and they start cooking dinner.
Problems can arise when the grid comes under maximum strain. Equipment can't cool off, and it can't handle as much power as usual. Lines, transformers and switches are working at full capacity and can be overwhelmed by power surges that can result from a blown piece of equipment or downed power line.
Even drops in power demand can be perilous. When a thunderstorm drenches a big, hot city, there is a quick drop in power demand because suddenly millions of air conditioners don't have to work so hard. When power flow changes rapidly, either because of a surge or a sudden dropoff, devices meant to prevent equipment failures could trip, cutting power to customers.
Peak summer demand can be nearly double the demand of a typical day in a mild month like April or October. The PJM Interconnection, which operates the transmission grid in parts of 13 mid-Atlantic states, hit a record peak demand of 146,082 megawatts Tuesday. That compares to a typical April peak load of 78,000 megawatts.
Utilities and grid operators have to plan for the summer peak year-round. For them, a summer heat wave is like Black Friday for a big box retailer. Customers are clamoring for service, and it is time to sell the most power at the highest rates of the year.
Power generators have fleets of small power plants that can be turned on and off relatively easily to meet demand. They are inefficient and expensive, and therefore push the wholesale price of power sharply higher. Peak summer wholesale prices can be triple the price of power during a mild-weather month.
By the end of May each year, utility emergency procedures must be finalized, equipment must be repaired and power plants prepared. Jim Meister, vice president of operations support for Exelon Nuclear, which owns 10 nuclear plants, says each plant undergoes an average of 100 maintenance activities a year to get ready for summer.
When a heat wave is predicted, alert levels are raised that slow and then stop all non-essential maintenance on the grid. Fuel is delivered to plants that may need to fire up and workers are put at the ready.
A long heat wave like this week's can put even more stress than normal on the system. When heat waves are short, some people will put up with a sweaty day or two. But when a heat wave lasts, many people make their homes colder than normal and run air conditioners constantly.
Also, air conditioners have to work harder because the persistent heat deeply warms walls and other infrastructure, making it harder to cool rooms.
"As you get into the heat wave, the load builds even if the temperature stays the same," says Mike Bryson, the Executive Director for systems operations at PJM.
Jonathan Fahey can be reached at www.facebook.com/Fahey.Jonathan