As electric generators age and get replaced the trend will likely be away from coal simply because it will be "next to impossible to get a coal plant permitted for construction," Lincoln Electric System Vice President of Power Supply Jason Fortik said.

Natural gas releases fewer greenhouse gases than coal when burned. But it remains controversial because of the fracking methods used to mine it from the ground and because if it leaks into the air without being burned it can contribute more in the short term to global warming than carbon dioxide.

There have been some small shifts away from coal in Nebraska.

NPPD plans to switch one of two steam boilers at Sheldon Station near Hallam to burn hydrogen instead of coal as part of a new venture with Monolith Materials Inc.

The California-based company plans to build a new plant next to Sheldon Station to produce carbon black, a fine, flourlike powder used in tires, plastic, inks and cellphones. Monolith will use electricity to extract the carbon from natural gas, producing hydrogen and water, then sell the hydrogen to NPPD as fuel.

Omaha Public Power District plans to retire three of its oldest coal-fired units at the North Omaha Generating Station this year and convert two other units to gas by 2023.