Lower Nuclear Output, Humidity Boost Eastern U.S. Power Prices

Lower output from two nuclear reactors combined with high humidity to drive up spot wholesale electricity prices across three grids stretching from eastern Illinois to Maine.

Public Service Enterprise Group Inc. reported that its Hope Creek 1 reactor in New Jersey tripped offline late Monday, while Exelon Corp. cut output at its Quad Cities 2 plant near Chicago to 24 percent early Tuesday. Both had previously been operating at full power, U.S. Nuclear Regulatory Commission data show. They’re also both on the 13-state grid operated by PJM Interconnection LLC.

The output reductions are pushing up power prices from PJM into the transmission systems operated by the New York Independent System Operator Inc. and ISO New England Inc. Demand on the three grids serving these regions is above forecast as households and businesses crank up air conditioners amid unusually humid weather, according to Genscape Inc. Rain is forecast later Tuesday.

“The nuclear power losses and strong demand in PJM is creating a ripple effect as they increase prices in New York ISO and ISO New England,” said Armagan Yavuz, a Boston-based analyst with Genscape. “It’s warmer and more humid ahead of this rain than everyone was expecting; once this rain hits, things will calm down. So it shouldn’t have an impact on tomorrow.”

Spot power at PJM’s benchmark Western hub, which includes Washington to western Pennsylvania, more than doubled, rising $60.56 to $96.58 a megawatt-hour in the hour ended at 3 p.m. from the same time Monday, according to grid data compiled by Bloomberg. Average spot on-peak prices, which cover the hours from 7 a.m. until 11 p.m., at the hub are up 38 percent at $76.93, heading for the highest daily average since Sept. 8.

Washington’s high temperature reached 81 degrees Fahrenheit (27 Celsius), 7 above normal, with humidity expected to hit 96 percent tonight, AccuWeather Inc.’s website showed. Boston’s high of 84 degrees was 16 above normal while Manhattan reached 13 higher than normal at 83.

New York City spot prices rose $12.20, or 31 percent, to $51.07 a megawatt-hour in the hour ended at 3 p.m. The gain helped more than double the on-peak average to $89.03 to the highest level since Sept. 8. Prices at the hub serving Boston and Northeast Massachusetts quadrupled to $141.48 and the spot average more than doubled to $80.54, the most since Sept. 17.

Higher-than-expected demand coinciding with lower nuclear generation is reducing flows of power from PJM into the New York state grid, prompting New York to cut exports to New England, Yavuz said.

Exelon plans to return the Quad Cities 2 reactor to full power within 24 hours after a pump trip reduced output, Bill Stoermer, a spokesman for the company, said in an e-mail. Workers were replacing a failed computer cell in the digital recirculation system, he said. Its nameplate capacity is 1,009 megawatts.

The Hope Creek unit shut after both reactor circulation pumps tripped just before 9 p.m. on Monday, the NRC report said. The nameplate capacity of the plant, about 18 miles (29 kilometers) south of Wilmington, Delaware, is 1,291 megawatts.

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