PJM presented a review of the Oct. 2 Performance Assessment Interval (PAI) to the Operating Committee Nov. 12, detailing the conditions surrounding the event and introducing recommendations to be developed in partnership with stakeholders.
The review marks the beginning of a discussion about lessons learned from the PAI, the first to affect generation resources under Capacity Performance rules, said Rebecca Carroll, director – Dispatch.
It does not have all the answers, she said, but PJM wanted to release as much information as possible in a timely manner to be responsive to stakeholders’ questions. PJM also has posted an FAQ.
Where Did the Load Go?
The PAI was implemented on the second, hotter day of an unseasonable fall heat wave that led to a variety of emergency procedures.
The biggest question remaining is why the demand for electricity did not materialize as forecasted Oct. 2.
“More work is needed to determine how much of the non-weather-driven load reduction during the PAI can be classified into the following categories: scheduled PJM [demand response]; over-responsiveness of PJM demand response; non-PJM, behind-the-meter load management programs; and industrial load response,” according to the 27-page report, the highlights of which Carroll presented and will be featured at other standing member meetings.
What Led to the PAI
On Sept. 30, PJM issued a hot weather alert for Oct. 2 for all zones but ComEd in Northern Illinois.
Oct. 1 ushered in hot weather across much of the PJM region, resulting in peak demand of more than 125,500 MW – about 5,500 MW higher than forecasted. Peak demand at this time of year is typically closer to 100,000 MW.
That evening, PJM called a Maximum Generation Emergency/Load Management Alert, an early warning that system conditions for the next day could require the use of PJM emergency procedures.
Given its experience Oct. 1, PJM also revised the load forecast for Oct. 2 to a peak of more than 132,000 MW, as temperatures were forecasted to be even higher in most of the PJM footprint.
Transmission Line Lost, 2,000 MW Unavailable
Early on Oct. 2, a 765 kV transmission line was taken out of service to isolate failed equipment, which heightened concerns about whether PJM would have enough capacity to serve load at peak demand.
Later that morning, PJM received word that as much as 2,000 MW of generation that was expected to be online for the peak would not be available.
At noon Oct. 2, PJM issued a two-hour lead time Pre-Emergency Load Management Reduction Action in the Dominion, Pepco, Baltimore Gas & Electric and AEP zones. This action triggered a PAI.
Temperatures Climb, Demand Doesn’t
Contrary to expectations, the Oct. 2 actual peak only reached 126,500 MW – even though the weather was warmer, with temperatures climbing 10 to 15 degrees higher than the previous day in some areas.
PJM is working to understand the difference between the forecast and the actual peak, Carroll said.
“For the load to only materialize at 1,000 MW higher was not intuitive at all to us,” she said.
Backcast Reveals Some Answers
The load forecast error was centered on four zones: FirstEnergy, AEP, ComEd and PJM Mid-Atlantic, with 90 percent attributed to these four, Carroll said.
Using actual weather conditions, PJM performed a “backcast” – that is, what the load forecast would have been if the weather could have been predicted perfectly.
If a backcast performs better than the PJM load forecast, that indicates that the error may be attributed to weather, Carroll explained.
In ComEd, that was the case, and unsurprisingly so: There, a cold front moved in Oct. 2 a little earlier than PJM had predicted.
What Happened in AEP?
That was somewhat the case in FirstEnergy as well, but not in AEP and the Mid-Atlantic zones.
There, Carroll showed on a slide, the backcast predicted even higher load than the errant PJM load forecast.
“So we can’t really attribute the forecast error to weather,” she said. “Some other behavior is happening there.”
Could Industrials Have Dialed Back?
AEP was one of the zones where load management had been called. Is it possible, one member asked, that the difference is significant load reduction by one or more industrial customers?
Joseph Mulhern, senior engineer – Generation, said PJM is looking at just that.
“We definitely attribute a significant amount of missing load to PJM demand response, but we don’t think enough demand response was dispatched to fully account for what we observed,” he said.
“We don’t have a lot of visibility down to the distribution level,” Mulhern added. “One of the limitations that we’re going to be working with is how much visibility down to actual customers we can get.”
More Analysis to Come
Carroll said PJM continues to drill down into the nodal load to try to find clarity.
PJM expects to have more details on demand response in mid-December, with more information to come from the January/February billing cycle that will factor in the PAI.
“We’ll certainly be back to the stakeholder community, potentially with issue charges to start to work through any opportunities we see coming out of our first experience here with a PAI that impacted generation resources,” she said.