A group of U.S. renewable energy developers has said it is willing to invest $6 billion in solar panels over the coming year — as long as they’re made here in America.

“Today, the maximum installed capacity in the U.S. is about 20% of demand. So first, you know, people are going to have to invest in expanding production facilities here in the U.S.,” said Andrés Gluski, CEO of the AES Corporation, which is part of the group.

The majority of solar panels used in the U.S. are manufactured in Asia, which wasn’t always the case. The U.S. was the leading producer of solar panels into the late 1970s.

Dan Kammen, an energy professor at the University of California Berkeley who also advises the White House on energy policy and global development, said that, with investment, the U.S. can become a major player in solar panel production again.

“It’s not like we’re building this from ground zero, from scratch,” he said.

U.S. companies have the knowledge to build these solar panels, Kammen said. It’s sourcing the inputs and building up the economies of scale that will take time.