The utility giant’s latest climate report, released Tuesday, argues that gas will remain a cheaper choice than batteries for backing up renewable power and closing coal plants. Even though it produces fewer emissions than coal, natural gas has increasingly come under fire from environmentalists, who want its use phased out as quickly as possible.

Duke plans to significantly cut back on its gas use as it works to have net-zero emissions by 2050. But the fuel will remain crucial for providing power when demand peaks and for balancing grids.

Relying on big batteries to reach that goal could cost three to four times as much as using gas, the report argues. Duke will also need its existing nuclear fleet and may also require advancements in long-term energy storage and carbon-capturing technologies.

“The fact of the matter is we are committed to this goal,” said Sarah Venuto, Duke’s vice president of public policy, in an interview. “That does not mean it’s going to be without challenges.”