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Case study: Wind lags responding to a power demand spike

It was no April Fool’s Day prank when the rate of a power demand increase spiked to its highest level of the year – 12.4% – on the morning of April 1st, 2013 in the Southwest Power Pool territory. Low seasonal and weekend demand overnight quickly reversed course as the business week began and utility customers started using more power.

The US Energy Information Administration analyzed this real-life scenario in its latest “Today in Energy” post titled “Rapid increases in electricity demand challenge both generating unit and system operators.”

“Because supply and demand for electricity must balance in real-time, rapid changes in demand create operational challenges for the electric system and generating unit operators,” the EIA said.

EIA power demand spike

“To satisfy this rapid increase in demand, system operators sent dispatch signals to numerous generators to increase their output … While coal-fired units in this instance provided about 70% of the increase in capacity during the peak ramp hour, natural gas-fired capacity increased its output at a higher rate than coal capacity (19% to 16%). This difference is because SPP relies more on natural gas-fired capacity for quick ramping and the output of natural gas generators is starting from a smaller base than coal generators. Wind output was flat during the peak ramp hour and declined after that.” – EIA

The wind component of the analysis is interesting and illustrates why integrating greater volumes of wind power into the grid is challenging without the ability to store it. “On the morning of April 1, wind capacity increased for the first half of the ramping period and decreased during the last half of the period. Because wind capacity is generally not dispatched by system operators and its output depends on the winds, the pattern of wind output can change significantly during the ramp period,” the EIA said.

Wind’s variability is often cited as a challenge for power system operators balancing real-time supply and demand. You cannot just turn a dial to increase or decrease wind capacity when the grid calls for more power. Without an energy storage breakthrough, or some currently unforeseen technological advance, it’s difficult to see how this obstacle can be overcome.