Instead, the 30 by 30 foot structures — scheduled to be completed this week — feature concrete, steel or a combination of both. Five are solid. Three have slats to see through to the other side.

Beauty, though, is in the eye of the beholder. One is painted royal blue. Another is stamped with a brick pattern, topped with sloped metal grating. All would evoke a prison feel if replicated for miles on end.

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 $20 million allotted for the prototypes and related infrastructure. (The prototypes themselves cost between $300,000 and $500,000 each.) Private citizens keen on controlling illegal immigration have taken up a collection, so far raising close to $15,000 — nowhere near the $21.6 billion the entire 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.

From across the border in Tijuana, a man watches a prototype of President Trump's U.S.-Mexico wall being built near San Diego on Oct. 12. (Guillermo Arias/AFP/Getty Images)

“At least 70 percent 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.”

People pass the border wall prototype in San Diego. (Gregory Bull/AP)

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 emphasized 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 $500,000 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 percent 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.”

A prototype of the border wall near San Diego. (Guillermo Arias/AFP/Getty Images)

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.