So is this is where the "great wall" dreams ends?
Congress has yet to agree to pay to build any piece of Trump's wall beyond the US$20 million ($29m) allotted for the prototypes. Private citizens keen on controlling illegal immigration have taken up a collection, so far raising close to US$15,000 ($21,000) - nowhere near the US$21.6 billion ($31.5b) the wall is projected to cost.
"I hate to say this, but it's a huge waste of money to do the prototypes," said Steve Vulich, co-founder and vice president of the America First Foundation, a nonprofit whose self-described purpose is to raise money for causes that lack sufficient funding - like the "Great Southern Wall."
Especially, he said, if there is no solar wall after all.
"At least 70 per cent of our audience who emails us wants solar panels. It should have been one of the priorities because they are going to need power out there," Vulich said.
"They are going to have to make it welcoming and environmentally friendly. I could do a computer model of a wall with solar panels with murals painted on it and it would just blow their minds."
Vulich said his organization is trying to work with Congress to figure out how to transfer the donated amount to the private contractors or to the U.S. Treasury.
"If they are not looking at it now in the prototypes, they darn sure should be looking at the ability of being able to add that on, once this wall is up," he said.
Trump said over the summer that the wall would pay for itself if it were made of solar panels.
"A solar wall. It makes sense. Let's see. We are working it out. Solar wall panels," he said at a rally in Iowa in June.
Pressed about it aboard Air Force One in July, Trump doubled down on the idea.
"Look, there's no better place for solar than the Mexico border - the southern border," Trump told reporters. "And there is a very good chance we can do a solar wall, which would actually look good."
Asked whether there could potentially be a solar revival down the road, if the wall is ever constructed, a spokesman for Customs and Border Protection responded with a statement by Mario Villarreal, division chief for the agency's San Diego field office, to the Washington Examiner last week: "We're certainly looking for different methods and ways to make this better. Solar panels or technology bundles on top of the fence certainly isn't off the table."
The spokesman emphasised that Villarreal was speaking about the future - as no solar panels are featured in any of the prototype designs.
Al Anderson, the general manager of KWR Construction, one of the firms awarded a nearly US$500,000 ($731,000) contract to build a steel prototype, told The Washington Post this week that solar panels were an impractical feature because "the federal government does not have a means to collect money from utility companies. So if solar panels were placed on the wall, there would be no way to reap any credit for the power that they produced."
Not to mention that with less than 2 per cent of the U.S. population living within 40 miles of the Mexico border, most of the electricity generated by the wall would be useless - unless costly transmission lines were also built to channel the electricity to other parts of the country.
"The idea that this is all going to be paid for by generating solar energy is preposterous," said Steve Ellis, vice president of Taxpayers for Common Sense. "It's just another piece of snake oil to help sell this plan."
Robert Weissman, president of the consumer advocacy group Public Citizen, said if Trump were seriously interested in advancing solar power, "there are a lot of very worthy things to do but building the wall is not one of them."
Instead, he said, Trump's Department of Energy is undermining solar by pushing for a rule that would force utilities to subsidize coal and nuclear energy at the expense of renewable energy.
The Federation for American Immigration Reform, which favors stricter immigration control, has proposed other ways of funding the wall, including charging a $2 passenger or pedestrian fee for all legal border crossings, increasing visa fees, and taxing remittances being sent to Mexico by non-U. S. citizens.
"Our only concern is that the wall is effective and that it gets built," said Dave Ray, a spokesman for the federation. "It if can generate electricity as well, then that's just sauce for the goose."
