The drop in wind output caught the grid operator, the Electric Reliability Council of Texas (ERCOT), somewhat by surprise. Fearing the advent of rolling blackouts it declared a state of emergency. In the event, no emergency occurred. But knee-jerk coverage of the episode gave the opposite impression.
Typical among prominent newspaper headlines were "Wind power snafu" and "The day the wind died in Texas." Fossil fuel energy executives jumped on their least loved competitor. David Crane, president of NRG Energy Inc, a major utility, was quoted as saying, "If a system can go unstable in the winter because 1500 MW of expected wind turns into 400 MW wind and then fossil has to scramble to come online...that's a big issue and there's going to be a big debate."
Publication of an ERCOT investigative report last month tells a different story. "What it clearly demonstrates was that the system we have in place to handle any unforeseen emergency -- whether wind or any other generation -- clearly worked," says Paul Shadler of The Wind Coalition, which represents the Texas wind industry. "We did not have an involuntary loss of power in the state, unlike other events that have happened."
The roughly 12,000 MW of wind assets powered down in a highly predictable way, at a rate of 8 MW a minute over three hours, states the report. The American Wind Energy Association (AWEA) points out that fossil generation shutdowns are almost always instantaneous drop-offs that are harder for grid operators to accommodate.
In justifying its decision to declare an emergency, ERCOT says a problem it could normally handle was compounded when a number of power plant other than wind failed to provide their promised volumes of electricity to the grid. During a 30-minute period in the early evening when non-wind generators had scheduled a drop in output of 50 MW, it instead dropped by 550 MW. Further, the day ahead forecast for needed power was far off the mark, with demand ramping up during a one hour period by 2550 MW instead of the predicted 1600 MW.
Ultimately, ERCOT used its "demand response" system to prevent any blackouts. The system operated by the grid operator, an acknowledged leader in managing demand, calls for large industrial customers to scale back their energy consumption during rare grid disturbances in exchange for a reduced overall electricity rate throughout the year. Roughly 11,000 MW of demand was pulled off to stabilise the grid.
New steps are being taken to reduce the chances of a similar incident occurring. Forecasts of wind power production by the wind industry accurately predicted the cold front and the resulting drop in wind energy availability, says Shadler. That forecasting, however, has not been a normal part of ERCOT's planning protocols.
"The ERCOT study does highlight the fact that there are improvements that can be made in forecasting," says Shadler. Indeed, the only actionable item that came out of the event is far from being a negative one for wind: ERCOT has indicated it is going to improve its forecasting technique. "I applaud that, we all applaud that, we think that's a great idea," says Shadler.