Should the US lean more on natural gas in its energy mix?

Natural gas could serve as a carbon-light ‘bridge fuel’ while renewable energy sources are still gaining ground in the US energy mix, a new study from MIT says.

By , Staff writer

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    Natural gas: A fleet of buses powered by liquefied natural gas wait at a terminal Santa Monica, California. A new study from MIT suggests that natural gas could serve as an important ‘bridge fuel’ along the way to a renewable-energy future.
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The US could get a running start at curbing its greenhouse-gas emissions by shifting its energy mix more rapidly toward natural gas in the next few years, allowing renewable energy sources like wind and solar time to gain ground, a study released Friday found.

Such a finding represents a big shift from just a few years ago. Back then, natural gas prices were spiking, and proposals to build terminals to import liquefied natural gas (LNG) seemed likely to make the United States reliant on one more imported fossil fuel. Both of those issues cast doubt on arguments that natural gas could serve as a carbon-light "bridge fuel," substituting for coal until more renewable energy arrived.

But new techniques for extracting "unconventional" natural gas locked in massive US shale formations have changed the picture, says the report from the Massachusetts Institute of Technology in Cambridge, Mass. Those new supplies make it likely that natural gas will take on a much larger role in curbing greenhouse-gas emissions by 2050, the study says. This could happen by replacing old, coal-fired power plants with far more-efficient, modern natural-gas turbine generators.

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“Much has been said about natural gas as a bridge to a low-carbon future, with little underlying analysis to back up this contention. The analysis in this study provides the confirmation – natural gas truly is a bridge to a low-carbon future,” said Ernest Moniz, director of the MIT Energy Initiative, in a statement.

Today, the US consumes about 22 trillion cubic feet (Tcf) of natural gas per year, and it holds reserves of about 2,000 Tcf – a 92-year supply at current consumption rates, the study found. These figures include the economically recoverable "unconventional" shale-gas reserves, which have risen 20-fold to more than 616 Tcf and have hiked overall US reserves nearly 50 percent.

By turning to more efficient "combined cycle" turbine-generator plants, instead of relying primarily on coal-fired power plants, the US could cut its CO2 emissions by more than 10 percent, the study found. In Texas, for instance, that approach would curb CO2 emissions by 22 percent without building any new plants, the study says. Other pollutants, like sulfur dioxide and nitrogen oxides, would also be reduced.

But there's a flip side. Energy efficiency and renewable energy hold the promise of cutting the use of natural gas in the long run, the study notes.

"Studies like this show the potential for natural gas to really break the grip of coal generation," says David Schlissel, a consultant on energy-resource planning in Cambridge, Mass. "But in the longer run, efficiency and renewable energy will have a big impact on cutting natural gas use, too."

According to a recent study by the US Energy Department’s National Renewable Energy Laboratory, wind generation could displace up to 50 percent of the electricity generated by natural gas by 2030.

Environmentalists are somewhat mixed on the report. On the one hand, they say, it's great to have the role of natural gas as a bridge fuel reinforced. But on the other hand, they’re concerned about hydraulic fracking, or fracturing – the method for extracting the shale gas, which injects a chemical underground that may pollute water supplies.

"We certainly don't oppose hydraulic fracturing or shale gas. But we want to get rid of the current exemptions this type of gas development has from US environmental laws," says Jim Presswood, an energy analyst at the Natural Resources Defense Council in Washington.

The report recommends that disclosure of all components of hydraulic-fracture fluids be required. It also recommends comprehensive polluted-water disposal plans.

As the hydraulic-fracturing debate continues, and Congress mulls whether to put a price on carbon emissions, the role of natural gas will surge – then give way to renewable energy, the report predicts.

"In a carbon-constrained world, natural gas will become a larger part of the energy mix,” said Mr. Moniz in the statement. But in the longer term, the US will need to shift to “essentially zero-carbon” sources, so “we better not get mesmerized by gas either.”

He added, “We need to do the hard work of getting those alternative technologies ready to take over.”

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