PJM’s Secret Recipe for Forecasting Thanksgiving Day Load

It’s a unique blend of human behavior, weather and – increasingly – renewable resources

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As millions of families prepare to share Thanksgiving dinner, PJM is cooking up something, too – a complex recipe for keeping the ovens running and the televisions humming as economically as possible on a day that is unique in its pattern of electricity demand.

“The day is literally like no other day of the year,” said PJM Senior Meteorologist Elizabeth Anastasio. “This is a day that’s really challenging.”

It is one of few days of the year for which PJM forecasts the demand for electricity, or load, independently. On these days – also New Year’s Day, Memorial Day, Independence Day, Labor Day, Black Friday, Christmas Eve and Christmas – human behavior changes the usual patterns of electricity use.

Forecasting models rely heavily on looking at similar past days. Any holiday that closes offices and schools begins to make a November Thursday look more like a weekend day. But human activity makes things more unpredictable.

It’s All About Togetherness

People are traveling – inside and outside the PJM footprint – and gathering at different times in different households, leaving other homes dark.

Families are cooking, and according to the most recent data on Thanksgiving electricity use  from the U.S. Energy Information Administration, 63 percent of households use an electric appliance to prepare food.

In addition, according to the Energy Information Administration, 59 percent of households report using the same fuel to heat their main spaces as they do for cooking. Even those that don’t tend to turn to electricity for secondary heating needs.

… And the Weather

Factor in the extreme highs and lows that have been creeping into fall temperatures, and there are few historical templates from which to choose.

“The more you restrict what type of day you can look for, the worse it is,” Anastasio said. “You look back and have three Thanksgiving examples, and if you don’t have a weather match, you’re out of luck.”

So, what would forecasters be thankful for?

“We wish for a day that’s exactly like a day in the past,” Anastasio said.

Watts for Dinner?

Marine Corps Community Services has broken down how much power in kilowatt hours (kWh) a typical Thanksgiving dinner takes to prepare for the more than 60 percent of households that use an electric appliance. (A kilowatt hour is a measure of energy use. It represents the energy you would use if you kept a 1,000-watt appliance running for an hour.)

  • Turkey (8 kWh) – enough to play video games for 55 hours
  • Stuffing (2 kWh) – enough to run a ceiling fan for 25 hours
  • Mashed potatoes (1 kWh) – enough to use a DVD player for 35 hours
  • Green bean casserole (1 kWh) – enough to watch TV for 65 hours
  • Pumpkin pie (2 kWh) – enough to power a laptop for 40 hours

Ask Again Next Year

Unfortunately, it doesn’t look like that’s going to be the case this year.

“Temperature-wise, this year is middle-of-the road as compared to the last three years. It will be much warmer than last year, but not as warm as 2016,” she said.

“There’s not a great match, weather-wise, so we’ll use those load curves (taking them with a grain of salt), the output of the models and our best judgement.”

The peak forecast is 85,717 MW at 11 a.m., though that estimate will be fine-tuned as the day nears. For comparison, an average November weekday since 2010 has seen electricity usage peak at 96,542 MW at 7 p.m.

As in other years, a second, broad evening peak, at about 6–9 p.m., is expected, as people stay up chatting or watching football before hitting the road.

House of the Rising Sun

An earlier peak – because of the festive dinner – is one of the characteristics that sets Thanksgiving apart from other holidays.

That may be changing, though, due to the impact of behind-the-meter solar – that is, solar generation not connected to the grid and therefore invisible to operators.

This was a surprise last year to ISO New England, where, for the first time since at least 2000, peak load didn’t occur in the morning.

Despite frigid temperatures, the day was sunny, and solar power lowered demand on the grid, pushing the peak load experienced by the grid until after sunset. 

PJM Already Lets the Sun In

PJM is prepared for this impact of increasing renewable resources, Anastasio said.

“Last year, we implemented a sister model to each of our load forecast models that takes into account behind-the-meter solar,” she said.

That doubles the number of computerized load models to 16.

Still, she said, “Our load forecast models are having a harder time than usual agreeing on a forecast for Thursday. But that’s where our forecasters come in!”

Feast on real-time grid conditions at pjm.com or on the PJM Now app.