PJM’s day-ahead prices for last Thursday turned out to be far more modest than they initially appeared.
The RTO reposted the day-ahead results for March 27 after officials identified an error in the input data used to clear the market. A value of 350 MW was used for the West Interface instead of 3,500 MW for hours 8 through 23, causing incorrect prices and quantities in the day-ahead market solution.
A glum Stu Bresler, vice president of market operations, informed stakeholders of the error at the end of Thursday’s Members Committee meeting. In reposting the results, Bresler said PJM was invoking a provision put in the Tariff “with the hope that we’d never have to use it.”
The changes reduced prices by as much as $37/MWh, with the biggest changes seen in the AECO, BGE, JCPL, METED, PECO, PPL and PSEG zones. In the PPL zone, for example, the LMP for hour 20 — originally posted at $89.41 — was reduced to $52.16.
Bresler said yesterday that the error resulted in higher day-ahead dispatch orders for some generators east of the West Interface and lower orders for those to the west, but that the actual dispatch of the units in real time was unaffected.
Bresler said the apparent constraint at the West Interface “didn’t bind that hard, so it wasn’t enough to raise a red flag” before the day-ahead results were initially posted.
He said officials are investigating whether they can add an automated check to prevent such errors in the future. “We certainly don’t want the market to think this is going to be a regular occurrence,” he said.
