Trump says solar Mexican border wall will 'pay for itself'

US President Donald Trump is planning to build solar panels on the wall he promised to build on the southern border and force Mexico to pay for.

The former Celebrity Apprentice host told a rally in Iowa about his plans, saying it was "my idea" and he had a "pretty good imagination".

Mr Trump said the panels could provide cheap energy and reduce the costs of building the wall, according to reports.

"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, right?" the President said.

Mexico's President Enrique Pena Nieto shot down the idea that his country would pay for Mr Trump's wall, insisting that would never happen.

The proposed barrier will stretch more than 3218km along the Mexican-US border, with cost estimates ranging from $21 billion to $38 billion. However, Democrats and even most Republicans reportedly doubt that the wall will ever be built.

More than 200 organisations expressed interest in designing and building the wall, including environmentally friendly options. However, some of the submissions were made in protest, with designs that allowed for the border to be easily crossed.

Twenty finalists have been selected to pass through the next stage of building a physical prototype.