President Donald Trump suggested to House and Senate Republican leaders this week that solar panels be installed on his proposed U.S.-Mexican border wall. Under his proposal, electricity generated by the panels could be sold into the grid, and the proceeds would help pay for the wall.

Coming less than a week after the White House pulled the U.S. out of the Paris Agreement, Trump’s sunny remarks to Hill leaders (first reported by Axios) were counterintuitive enough to cause some to wonder. Wait. Could that actually work?

Customs and Border Protection issued a request for proposals in mid-March for the border wall. By the April deadline, CBP had received pitches numbering in the “low hundreds,” according to a May 2 update on its website.