Renewable energy information services provider 3TIER in July confirmed with its publication of wind performance maps what U.S. wind developers with poor generation numbers had been suggesting earlier this year: A long-lasting El Niño event paired with a North Atlantic Oscillation event caused wind speeds to slump abnormally from the fall of 2009 through spring 2010.
The second quarter of 2010 showed a significant increase in wind intensity (Figure 3). The upswing was in mainly the western U.S., from Washington State to Texas, where generators experienced above-average wind speeds. The increase was due to a weakening of the climactic phenomena. “As a result of waning climatic events, [the second quarter of 2010] experienced prevalent storm activity off the Pacific Coast, which played a large role in the overall wind speed increases,” 3TIER said.
|3. An ill wind. From the last quarter of 2009 through the first quarter of 2010, a long-lasting El Niño event, paired with a North Atlantic Oscillation, caused wind speeds across the U.S. to slump abnormally (top). The second quarter of 2010 (bottom), however, showed a significant increase in wind intensity, mainly for western U.S. states, from Washington to Texas. Texas saw such a great increase that its second quarter recovery pushed its six-month average above normal. The event shows how quickly wind resources can change. Courtesy: 3TIER|
Despite the positive trend, almost all regions of the U.S showed below-average wind speeds for the period of January through June. The exception was Texas, which saw such a great increase in wind speeds in the second quarter that the recovery pushed its six-month average above normal. The event shows just how quickly wind resources can change, 3TIER said, underlining the importance of incorporating long-term wind performance and anomaly studies into the design and due diligence process for wind energy projects.
The global impact of El Niño—a climate pattern in the Pacific Ocean that happens every three to seven years, stemming from changes in oceanic surface temperatures—on renewable generation has put entities like Texas grid operator Electric Reliability Council of Texas (ERCOT) and wind developers like Infigen Energy on the alert.
That Australian company, which operates 1,089 MW at 18 wind farms in Texas, Oklahoma, and Illinois, said in February that it saw an 8% reduction in total power generation through the end of 2009 and the beginning of 2010—“reflecting the lowest average actual wind speeds in the last 30 years,” the company told investors. Infigen went on to propose that an El Niño phenomenon was to blame, and though it was not expected to have a material impact on its long-term generation estimates, the strength and duration of the climate mechanism was difficult to forecast.
Meanwhile, after seeing a new high for instantaneous wind output of 6,272 MW this March—which served 19% of the total load at the time—ERCOT implemented a forecasting tool designed to help system operators prepare for large and sudden changes in wind production.
The new tool developed by AWS Truewind in collaboration with ERCOT system engineers is meant to help the grid operator gauge “wind ramps”— large and rapid changes in wind power production, which can be caused by air mass changes, thunderstorms, cold fronts, nocturnal stabilization, pressure changes, and other transient atmospheric events. The alert tool makes calculations six hours ahead to warn system operators of the risk of large and rapid increases or decreases in wind output.
Additionally, the ramp forecast calculates the values of magnitude and duration, and estimates the probability of a large ramp event beginning in a particular interval. Information regarding the weather event that is most likely to cause large load swings is also included, as well as additional characteristics for each predicted ramp event, such as most likely start time, duration, and maximum ramp rate.
“With the increased percentage of the system load served by wind, it becomes critical to have not only a good forecast of how wind will generate during the day, but also an assessment of the level of uncertainty in that forecast,” said Kent Saathoff, ERCOT’s vice president of system planning and operation. “Since we don’t have much control over wind, the key for grid reliability is to have a good wind forecast, and be prepared for the variability of wind as we are for load, rather than as a controllable capacity resource.”