Abstract :
The Electric Reliability Council of Texas (ERCOT) experienced record weather extremes in 2011. During the morning of February 2 the coldest temperatures and wind chills seen in over 20 years caused an unprecedented amount of generating capacity to trip off-line or fail to start due to frozen instrumentation and controls. At the same time, customer demand for electricity was approaching record winter peak levels. In order to prevent an uncontrolled drop in system frequency, ERCOT implemented its Energy Emergency Alert (EEA) plan. Through the morning almost 1,500 MW of interruptible load was dropped and up to 4,000 MW of firm load was subjected to rotating outages until early afternoon. Preparation s ERCOT made for the frigid temperatures and the sequence of events will be discussed, along with lessons learned by generators, transmission and distribution utilities and ERCOT from the experience. These lessons learned benefitted ERCOT operations during another period of cold weather the following week and also proved their value a few months later during summer operations when all available generating capacity was needed. The summer of 2011 also presented severe operating challenges for the ERCOT electric grid. The summer was the hottest in recorded history in Texas with an unprecedented 12 month drought and records set for the number of days with high temperatures exceeding 100 degrees. Electric demand exceeded that which would be expected with normal summer temperatures by 8%. Electric generating plants were stressed to their limits to meet the high and persistent customer demand. The system was most stressed during August when demands reached their highest and generators began showing the effects of several months of operating at their maximum capacity. ERCOT implemented its EEA plan on seven days during the summer and shed interruptible load on two of those days in August. ERCOT managed to avoid any rotating outages during the hottest summer in history. There were - number of lessons learned from operations during the summer of 2011 that will be discussed. The importance and benefit of communications with the public, news media, public safety authorities, regulators and legislators about system conditions was proved. The assistance provided by increased coastal wind generation during summer days was also shown. In addition it was learned that long term projections of generation reserve margins can be misleading when applied to the short term and ERCOT is changing the way it presents resource adequacy reports in the future.
