By Amanda Durish Cook
CARMEL, Ind. — MISO is seeking to fine-tune its forecasting of wind generation as it faces the prospect of immense volumes of new capacity coming onto its system by 2023.
Speaking at an April 23 wind forecasting workshop, MISO forecast engineer Blagoy Borissov said the event was a “first step” in the RTO’s attempt to be transparent about its forecasting procedures and how it can improve the process.
“The timing for us is right to start having a conversation about wind forecast accuracy,” Borissov said. “In just four short years, we’re going to go from 19,000 MW to 29,000 MW of wind generation.”
He also pointed to the frequency of MISO setting new wind output records: The latest, 16.3 GW, was set on March 15.
The RTO predicts it will have more than 22 GW of wind in its system by the end of the year, rising to 29 GW by 2023. It had just 5 GW when it began its wind forecasting process in 2008.
Borissov stressed that the accuracy of MISO’s intermittent forecasts is imperative to ensuring that committed generation can meet expected load. When forecasted wind generation doesn’t materialize, the RTO must make additional commitments.
Under current practice, market participants can employ their own wind forecasts or rely on MISO. The RTO’s short-term wind forecast is updated both hourly and during every dispatch interval using five independent weather prediction models and detailed unit information that owners submit. The RTO uses the hourly forecast to satisfy must-offer requirements in the day-ahead market, while it uses the five-minute forecast for dispatch.
Where wind generators create their own forecasts, MISO incorporates that data into its models instead of filling in its own. If a resource owner fails to update its wind forecasts at least every 30 minutes, MISO reverts to using its own data in the forecast.
But MISO said it sometimes receives inaccurate forecast data from wind operators, hampering predictions of the actual generation capability of wind units.
“It definitely impacts how our wind forecasts are produced,” MISO forecasting engineer Dorsana Desai said.
Comparisons have shown that MISO’s forecasts are more accurate than those of operators, Desai said. The RTO creates standby forecasts for wind units even when they elect to furnish their own forecast data.
Market participant forecasts also suffer from a positive bias, with unit operators tending to over-forecast their generation. MISO also said it sometimes receives imprecise commercial operation dates from wind operators, compounding forecast inaccuracies.
MISO will begin performing a quarterly study to identify forecasting inaccuracies, Desai said, and email unit operators that repeatedly forecast output outside of a band of reasonableness determined by the RTO.
For its part, MISO is working to improve a time lag in its forecast algorithm, Desai said.
The forecasting workshop is in part a response to the RTO’s most recent maximum generation event, in which an inaccurate wind forecast contributed to an emergency declaration. During the Jan. 30 event, wind generation stayed well above its 2.3-GW capacity requirement that day based on Planning Resource Auction clearing. However, the RTO’s wind forecast had predicted many more wind offers into the market.
Wind output during the morning peak was about 4 GW below forecast as the worst of the cold struck the Midwest. It averaged 4.3 and 4.7 GW on Jan. 30 and 31, respectively, compared with about 13 GW for the two days prior to the event. MISO said the missed wind forecast was likely because the RTO did not factor in extreme weather cutoffs. (See MISO Details ‘Uncertainty’ Behind Winter Max Gen Event.)
“MISO has never experienced these extremely cold temperatures with the amount of wind generation we have today,” Ron Arness, the RTO’s director of central region operations, explained at a Market Subcommittee meeting in March.
In response, MISO is seeking to update the operational details of wind units by reaching out to generation owners to learn what might have changed. It will also evaluate how extreme events affects wind forecasting.
“Some of these wind units were registered eight, 10 years ago. … Maybe the information we got from the wind farms is no longer accurate,” Desai said, adding that wind operators could have since installed new technology that might affect operation of their units. She said MISO plans to reach out to all wind operators.
Beyond that, MISO is also examining using entirely new models or research to alter its wind forecasting process. Desai said such changes would represent a long-term effort, and stakeholders shouldn’t expect a major proposal any time soon.
