National Grid, the owner of Long Island's largest electric-generating stations, expressed support Monday for new federal rules to limit plant emissions, saying its generators are already largely compliant and could cut emissions further.

But a coal-fired unit across the Long Island Sound may be in regulators' crosshairs.

The Environmental Protection Agency Monday issued new guidelines designed to cut power-plant carbon dioxide emissions 30 percent by 2030.

The rules, expected to be finalized in 2015, take aim primarily at older, dirtier plants that burn coal, which provide about 40 percent of U.S. energy production. They aim to promote cleaner, more efficient plants, adopt measures to reduce energy consumption and expand renewable energy sources. The goal is to curb greenhouse gasses and reduce health and environmental impacts.

Long Island power plants no longer burn coal, though undersea cables linking Long Island to outside electric grids are supplied by plants that do. It is uncertain if closure of those plants would impact rates here.

Long Island power plants owned by National Grid -- which supply about half of the Island's power via three big steam plants and other smaller units for peak demand periods -- are fueled primarily by natural gas. Most of the big plants have seen emission-reducing retrofits over decades of use.

Accordingly, National Grid is raising no objections to the rules. "We support the new ruling as it allows flexibility at the state level and we are confident we will be able to realize additional emission reductions and achieve the levels set forth in this new EPA rule," spokeswoman Wendy Ladd said.

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In addition, she said, New York State's emissions rules are more stringent than elsewhere in the country."

LIPA spokesman Michael Deering referred questions to PSEG Long Island. LIPA has long-term contracts to use the entire National Grid fleet on Long Island and pays the cost of upgrades. It is currently considering a major overhaul of the E.F. Barrett plant in Island Park, to make the plant one of the region's most efficient. Ladd said repowering the Barrett plant would help meet the new rules by lowering its "carbon intensity."

In any case, National Grid is "well positioned to comply" with new rules, she said, because of the upgrades it has made to the biggest plants, in Northport, Island Park and Port Jefferson, all of which burn natural gas and fuel oil. Across Long Island Sound, however, PSEG Power, a sister company of PSEG Long Island, may be affected. PSEG Power operates a coal-fired plant in Bridgeport, Connecticut, and has already been under pressure from environmentalists to close it.

The company has said the plant, which opened in 1967, is "important to the reliability of the [electric] grid," particularly in winter, when the prices of natural gas and heating oil surge. Power from the plant is available to Long Island on the New England spot-energy market via the Cross-Sound cable.

PSEG spokesman Michael Jennings said the company favors "an economywide, market-based mechanism," to control emissions. Nevertheless, he said it supports providing incentives for energy providers "to reduce carbon emissions in a reasonable time frame."

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PSEG calls the 395-megawatt Bridgeport plant, which burns coal and fuel oil, one of the nation's cleanest coal-fired units. It's unclear whether the EPA rules would force further upgrades or closure.

Ross Ain, president of Caithness Long Island, which owns a 350-megawatt plan contracted to LIPA in Yaphank, and plans to build another more than twice as large, said: "We support the direction of the program to reduce global warming gases and take actions against man-made causes of climate change."

Ain said the EPA rules were "consistent with our business activities in developing renewable energy projects and state-of-the-art clean natural gas-fired projects which helps to reduce the electric industry's production of carbon dioxide in the production of power."