A string of hot and humid weather has put a strain on the electric grid across the United States this summer. But for the most part, demand for electricity has been met and the power grid has withstood its toughest test since 1999. Although it wasn’t all that long ago when electric usage typically peaked in the winter, summer peaks are now a given in most areas, and many regional and utility-specific record peaks were set this summer. According to the Edison Electric Institute in Washington, D.C., the total U.S. electric output set a new record in July with 95,259 gigawatt hours, 5 percent higher than the previous record set in August 2002. In New England electricity use reached 26,922 megawatts on July 27, surpassing the previously established record of 26,749 MW set a week earlier. Only a few years ago in New England there were more power plants in the works to be built than anyone thought necessary, but now there is talk about possible brownouts if more power plants are not built in the near future. Records were set by PJM Interconnection LLC of Valley Forge, Pa., which coordinates the movement of electricity among 13 states ranging from Illinois to North Carolina, and serving about 51 million people. On one day it transmitted the world’s largest-ever electric load, 135,000 MW. The New York Independent System Operator set a new record high of 32,075 megawatts in July, breaking a previous all-time high set exactly a week earlier of 31,741 MW. The demand for power in the Midwest ISO, which manages the grid for more than 36 million people in 15 Midwest states and the Canadian province of Manitoba, set an all-time high of 111,614 megawatts on July 25, breaking the old record of 108,705 MW set on June 27. Energy strains The surging demand this summer provided another big test for the nation’s power grid. In August 2003, a big Northeast blackout disrupted service to 50 million people, and two years earlier, soaring prices and isolated blackouts rolled across California, caused in part by Enron and other electric wholesalers manipulating the power supply. Since those events, regulators and power companies have made changes in their operations designed to help them stay abreast of system conditions and head off problems. So far, the improved planning, combined with the addition of a number of new power plants, seems to have helped the system’s reliability. The omnibus energy bill recently signed by the president also could bring changes by putting in place enforceable electricity transmission reporting and reliability standards that could force further improvements. The run-up in demand used up a cushion of surplus power that has moderated prices in recent years. That increases the risk of supply problems developing in a few areas. It isn’t just the heat and humidity that put a strain on the electric grid — long-term trends also play a role. In a report in the Philadelphia Inquirer, a Pennsylvania Electric Co. spokesman said that, since 1993, average household use among PECO customers has climbed 21 percent. The rise was attributed to stable prices coupled with lifestyle changes that include bigger houses, higher-pitched roofs that are less energy-efficient, air-conditioning added to older homes and a proliferation of appliances and electronics, like more DVDs, more TVs, and more computers, as well as two refrigerators in some households. Con Edison, which serves many customers in New York, also says that overall electric consumption has grown by nearly 20 percent over the past 10 years. In 2004, the company estimated that its customers used more than 8 million televisions, 10.5 million cell phones, 2.5 million personal computers, and 5 million room air conditioners, with customers expected to install an additional 900,000 units over the next five years. It’s not just peak usage that worries utilities and grid operators that run the transmission systems of several utilities but the fact that the heat came early this year and was sustained across huge areas. California suffered 14 consecutive days of demand topping 40,000 megawatts — an unusually long period of sustained high demand. “You get equipment failures that force power plants to drop off” when demand stays high, said Stephanie McCorkle, spokeswoman for the California Independent System Operator in Folsom, Calif. Such circumstances can quickly slide into a widespread shortage. nhbr Doug Patch, former chairman of the New Hampshire Public Utilities Commission, is with the Concord law firm of Orr and Reno.