NEW YORK — This will almost certainly be a record-breaking year for the advance of solar and wind power across the U.S. The additions that are in progress or planned are significant enough to boost hopes for emissions-free electrical grids within a generation — if natural gas doesn’t get in the way.

It just may. Gas is such a bargain that it’s being viewed less as a bridge fossil fuel, driving the world away from dirtier coal toward a clean-energy future, and more as a hurdle that could slow the trip down. Some forecasters are predicting prices will stay low for years, making it tough for states, cities and utilities to achieve their goals of being zero-carbon in power production by 2050 or earlier.

“The fact that there’s an abundance of it makes the move to complete decarbonization much harder,” says Ravina Advani, head of energy, natural resources and renewables at BNP Paribas SA. Gas is a tough competitor. “It’s reliable and it’s cheap.”

The flood of inexpensive gas does have a big environmental upside, because it’s putting increased pressure on struggling coal plants that contribute significantly to global warming. But it’s also squeezing margins for nuclear reactors, which are the U.S.’s biggest source of carbon-free power. And it’s driving utilities to lay down infrastructure that could ensure gas remains central to the power mix for decades.

Solar and wind are certainly winning in many markets on price alone. Without cheap gas, though, the renewables build-out would be faster, says Cody Moore, head of gas and power trading at Mercuria Energy America LLC. “Absolutely, 100 percent.”