Doing something about the weather

ESO Meteorologist Walshe making degrees of difference in load forecasting

By MYRA IRELAND

	Because weather is such a crucial factor in load forecasting, Electric System Operations hired a meteorologist, Patrick Walshe, with rewarding results.

“Predicting the weather as accurately as possible is the key to optimizing use of the TVA power system,” says Van Wardlaw, Vice President of Electric System Operations in Transmission/Power Supply.

“ The weather is the crucial factor in determining the load forecast, which is then used to plan generation for the following day. Which units are needed to serve the load? Can planned maintenance be performed? Are power purchases needed? Is there excess generation that can be sold? All of these decisions are critical to TVA’s bottom line.”

Historically, the accuracy of TVA’s load forecast reflected the average error in temperature forecasts, which was around the 3-percent level from 1998-2001. Chief Operating Officer Ike Zeringue thought the margin of error could be improved if TVA had its own meteorologist, instead of depending on predictions of others.

And he was right. This past year — the first that ESO Meteorologist Patrick Walshe has been with TVA — the accuracy of TVA’s weather forecast was the best in five years, improving to a 2.5-percent Mean Average Percent Error.

“ Back-to-back load-forecast errors of less than 2 percent were recorded for the first time ever in October and November,” Walshe says. “This forecast improvement of about 150 MW for all hours helped TVA make better asset decisions that resulted in cost savings and improved reliability for our customers.”

Hiring Walshe was just the first step toward improving load forecasts. Enhancing the incoming weather data and the model used to forecast TVA’s load followed.

Walshe worked with the current weather-data vendor to improve the forecast for the Tennessee Valley.

“ I explained to the vendor our pain level when the forecast is off,” he says. “We realized that the vendor’s least-experienced personnel work during the night, yet it is the early-morning forecast that TVA depends on so heavily, because that’s when we are committing generation.

“ When I don’t agree with their forecast, I give the folks there a call, and we talk about it. We have adjusted the temperature forecast by as much as 3 to 4 degrees, but their forecasts are much more accurate now.”

Walshe says the vendor’s temperature-forecast error has fallen to below 2 degrees for a record six months straight.

Another improvement in weather data is a newly installed “weather wall” in the System Operations Center. It provides Walshe with several additional sources of weather data to fine-tune the forecast for the Valley. A National Oceanic & Atmospheric Administration Port will be added next month to provide raw information from the National Weather Service satellite.

Walshe also looked at the load-forecasting model into which the weather data is fed. The original model used one piece of weather data for the entire Valley — a weighted average of the temperature for Memphis, Nashville, Knoxville, Chattanooga and Huntsville — even though the weather can vary significantly from one end of the Valley to the other.

The new model takes the weather data for all five cities into account individually and gives a more accurate load forecast.

Currently TVA is using both models to determine which one performs better under what conditions.

ESO’s Wardlaw says while TVA has made great improvements in the accuracy of its load forecasts, it’s an ongoing process improvement.

“ The weather can be our greatest friend or biggest adversary,” he says. “Our challenge is to accurately predict what tomorrow will bring and then to use our assets wisely.”

January 2003

Reducing TVA’s delivered cost of power

Patrick Walshe’s day

Patrick Walshe’s day begins well before most.

By 6 a.m. he’s at his home computer, poring over weather data. At 8:30, the Morning Call gets under way to set the agenda for the day. At 10:30 he attends the Bulk Power Trading briefing.

Throughout the day, Electric System Operations Meteorologist Walshe checks new weather data and tweaks the forecast, which must be ready by 2 p.m. to prepare the load forecast for the following day.

Weather is not only Walshe’s job, it’s his hobby. Evenings and weekends also find him at his home computer. Early on Saturday morning, Nov. 9, when bad weather heading for the Tennessee Valley looked worse than originally predicted, Walshe was on his phone from home, alerting others to make preparations for the violent storms and tornadoes that struck that weekend.

In addition to providing weather data for load forecasts, Walshe looks at emerging conditions and sends weather alerts to Transmission/Power Supply, Customer Service & Marketing and other TVA organizations. His forecast can be checked by clicking on the Weather Desk, found under ESO on the TPS homepage on TVA’s internal Web site.

— MYRA IRELAND