U.S. President Donald Trump said he¡¯s proposed building a ¡°solar wall¡± on the Mexican border that would pay for itself by generating electricity.

¡°We¡¯re thinking of something that¡¯s unique, we¡¯re talking about the southern border. Lots of sun, lots of heat,¡± Trump said at a campaign rally in Cedar Rapids, Iowa. ¡°We¡¯re thinking about building the wall as a solar wall, so it creates energy, and pays for itself. And this way Mexico will have to pay much less money, and that¡¯s good. Is that good?¡±

Trump ran for the presidency on an oft-repeated promise to construct a wall across the 1,933-mile (3,207-km) Mexican border to stop undocumented immigration. His speech in Iowa was the first time he has publicly described his proposal to build the wall as a solar power plant, though Politico previously reported that he privately floated the idea to Republican members of Congress in a White House meeting on June 6.

¡°Think about it, the higher it goes, the more valuable it is. Pretty good imagination, right, good?¡± Trump said in Iowa. ¡°My idea.¡±

Trump¡¯s first full-year budget, released in May, proposes a $1.6 billion down payment for new and replacement sections of a border wall. The president has estimated that completing the barrier would cost $8 billion to $12 billion, though many experts say the actual cost would be far higher.

His proposal has been met with a cool reception in Congress, where lawmakers of both parties have questioned the utility and cost of a physical barrier across the entire length of the border.