April 15, 2008

Reducing gridlock

Dr. Robert Peltier, PE, Editor-in-Chief

New grid sensitivities

Recent events confirm that even the best-oiled machine won’t operate at peak efficiency if an operator goofs or if Mother Nature decides to remind us who’s really in charge.

The Los Angeles Times’s main headline on February 26 was “Massive power outage in Florida affects millions.” The ensuing story described a mid-day “transmission glitch” at a West Miami substation that knocked out electricity to three million people and tripped two reactors at the Turkey Point nuclear station. Florida Power & Light later explained that an engineer had deactivated two levels of relay protection at the West Miami substation to help diagnose a switch malfunction. While he was making measurements, a short-circuit knocked 3,400 MW off-line.

That same day, Reuters’ lead story was “Loss of wind causes Texas power grid emergency.” ERCOT reported that the normally stable frequency of its grid dropped suddenly when the state’s wind production fell by more than 1,400 MW over 30 minutes. This loss of load forced ERCOT to go to Stage Two of its emergency electric curtailment plan and shave 1,100 MW of demand from industrial customers. The emergency passed in about three hours.

A 2007 study of the ERCOT grid noted that wind energy is “anti-correlated” with load, meaning that wind speeds—and wind power generation—usually drop sharply as the day’s load rises in the morning and then pick up again as day turns to night and demand falls. The study also concluded that putting more wind capacity on-line requires dispatching more conventional capacity to maintain grid voltage and frequency.

The Texas legislature recently learned from ERCOT that the state’s reserve margin will be about 13% this summer but will fall below 12.5% next year. Overall, peak demand is expected to rise more than 25% over the next 20 years. ERCOT’s CEO said at a March KEMA conference that the state must nearly double its generating capacity by 2026 to meet growth in demand and to replace retired plants. In other words, the 5,000 MW of wind projects in the ERCOT queue will do nothing to improve the reliability of Texas power.