National Geographic : 2010 Jul
in dense cities. "There's a need to build new lines," Dotter said. "But no matter where you propose them, people don't want them." Dotter pulled o the turnpike in the middle of nowhere. A communications tower poked above the treetops. We drove onto a compound surrounded by a security fence. Soon we were in the bunker, built by AT&T during the Cold War to withstand anything but a direct nuclear hit and recently purchased by PJM to serve as its new nerve center. In the windowless control room, dominated by a curved wall of 36 computer screens, dis- patch general manager Mike Bryson explained what I was seeing. A dynamic map on one of the screens showed the PJM part of the grid. Arrows represented major transmission lines, each with a number showing how much juice was on the line at that moment. Most of the arrows pointed west to east: In the eastern U.S. electric- ity ows from major power plants in the heart- land toward huge clusters of consumers along the eastern seaboard. At that moment PJM lines were carrying 88,187 megawatts. "Today is a mild winter day---I don't think we'll have over 90,000," Bryson said. e computers take data from 65,000 points on the system, he explained. ey track the ther- mal condition of the wires; too much power ow- ing through a line can overheat it, causing the line to expand and sag dangerously. PJM engineers try to keep the current alternating at a frequency of precisely 60 hertz. As demand increases, the frequency drops, and if it drops below 59.95 hertz, PJM sends a message to power plants asking for more output. If the frequency increases above 60.05 hertz, they ask the plants to reduce output. It sounds simple, but keeping your balance on a tightrope might sound simple too until you try it. In the case of the grid, small events not under the control of the operators can quickly knock down the whole system. Which brings us to August 14, 2003. Most of PJM's network escaped the disaster, which started near Cleveland. e day was hot; the air conditioners were humming. Shortly a er 1 p.m EDT, grid operators at First Energy, the WAS MADE AN INSTANT AGO, MANY MILES AWAY. ENERGY STORAGE Because wind and solar power are intermittent, the quest is on to find ways to store energy for round-the- clock distribution---fueled in part by $185 million in stimulus money. Here are four promising technologies. ART: BRYAN CHRISTIE SOURCES: U.S. DEPARTMENT OF ENERGY; ENERGY STORAGE ASSOCIATION; ESKOM Flywheel storage In one town in Australia, electricity from wind turbines powers flywheels; their spinning motion is used to regener- ate electricity when it's needed. Pumped-storage hydropower Water is pumped uphill into a reservoir when electricity demand is low and released again to turn a turbine when demand is high. Compressed air, stored underground An Iowa wind farm plans to pump air into sandstone for- mations when there's wind. Later the air can be released to make electricity. Sodium-sulfur batteries Pioneered in Japan, this technology can store a large amount of energy in a small space, as lithium- ion batteries do for electric cars.