The regional power-grid operator has called out the Sierra Club of New Jersey after the environmental group last week said a controversial power-plant conversion would overload the transmission system.

The chief planning official for PJM Interconnection Inc., the grid operator, said in a letter to New Jersey Sierra Club director Jeff Tittel that continued operations of the B.L. England power station in Cape May County would not create reliability problems, but that the plant's shutdown would.

"Recent media statements attributed to you about reliability and cost impacts associated with the B.L. England generating units' remaining in service are based on a misunderstanding of PJM Interconnection's planning process," Steven R. Herling, PJM's vice president of planning, wrote Thursday to Tittel.

The spat is the latest skirmish over plans to convert the plant from coal and oil to natural gas. The Sierra Club has sought the closure of the plant, and has led efforts to block approval of a gas pipeline crossing the protected Pinelands to fuel the plant.

The New Jersey Department of Environmental Protection in July extended the plant's license for two years after PJM concluded that its shutdown next year would result in "immediate" transmission problems that could lead to brownouts.

The Sierra Club last week held a news conference to announce that a new PJM planning report had arrived at an opposite conclusion: If the plant is not retired next year, the transmission system will need to be fixed.

"This report is a game-changer," Tittel said last week. "It clearly shows that this plant is not only unnecessary, but will actually hurt reliability in the region."

The report Tittel cited was two slides in a 125-slide PowerPoint presentation at the Sept. 2 meeting of PJM's Transmission Expansion Advisory Commission.

Herling said the slides addressed reliability problems that would occur only if the plant's existing units were operated simultaneously with new gas-generation units. Herling said that such a doubling of generation was unlikely, but that PJM needed to consider and plan for it.

"Simply put," Herling wrote, "the continued operation of existing generating units at the B.L. England site, absent the addition of significant amounts of new generation, is not projected to result in reliability problems."

PJM has not calculated the cost of transmission-system changes that would be required if the plant were upgraded - the project was delayed after the Pinelands Commission rejected plans to build the gas pipeline. But PJM has identified $143 million in grid improvements needed if the plant retires.

"Our transmission-planning process is very complex, dynamic, and - as a consequence - can be misunderstood," Herling said in his letter to Tittel. "I would have been very happy to explain the process and underlying facts to help you avoid confusion, and would be willing to clarify PJM's study results at any time."

Tittel on Monday stood by his group's claims and said PJM was changing its story at the behest of utilities. "They're trying to spin it any way they can," he said.

The Sierra Club says that rather than being converted to natural gas, the plant should be replaced with renewable wind and solar energy.

B.L. England is owned by Rockland Capital Energy Investments L.L.C., of Houston.