Energy Secretary Dan Brouillette suggested Thursday that the United States could eventually use entirely renewable energy, a rare acknowledgment from an official representing the Trump administration, which has sought to boost production of fossil fuels.

Brouillette was testifying at a congressional hearing on the Energy Department’s fiscal year 2021 budget request. The proposed budget seeks to boost the development of energy storage technologies that can hold excess wind and solar energy for use when the sun isn’t shining and wind isn’t blowing.