President Donald Trump publicly proposed the idea of a “solar wall” on the Southern border, to help pay for the building costs.

“Solar wall panels, beautiful, I mean actually, think of it. The taller it goes the more valuable it is,” Trump said during a rally in Cedar Rapids, Iowa.

Trump said that there was “lots of sun” and “lots of heat” on the Southern border, which would allow the wall to create energy and help pay for construction costs.

“This way Mexico will have to pay much less money, and that’s good,” Trump said. “We’ll see.”

Trump reportedly floated the idea of a solar wall during a meeting with Congressional leaders in June, but hasn’t publicly confirmed the reports.