Boys play around, climbing the wall between Mexico and the United States in Ciudad Juárez, Mexico. (Herika Martinezherika Martinez/AFP/Getty Images)

U.S. Customs and Border Protection plans to select four to eight firms in the coming weeks to build the prototypes for President Trump’s much-touted border wall, Ronald Vitiello, the agency’s acting deputy commissioner, said Tuesday.

The administration's update on its plans for the wall comes amid delays in the bidding process and a seeming lack of political will to fund a continuous barrier along the 2,000-mile Mexico border.

The prototypes — including a reinforced concrete barrier wall as well as one made of an alternative material with see-through capability — will be built in San Diego.

Firms are expected to complete construction by September, within 30 days of their selection, Vitiello said.

More than 200 companies responded to the federal government’s two requests for proposals for the border wall in March. Customs and Border Protection had initially planned to award contracts by June 12, with construction beginning by July 21, according to a recent Homeland Security Inspector General’s report.

The June 12 report highlighted a history of delays and lack of oversight when it comes to border security.

“Most of DHS’s major acquisition programs continue to cost more than expected, take longer to deploy than planned, or deliver less capability than promised,” the report said. “DHS sometimes approves moving forward with major acquisition programs without appropriate internal oversight.”

Vitiello said Tuesday that the agency has entered the second phase in evaluating contract proposals. He would not say how many companies are in contention, but said it was a “substantial group.”

“We are on schedule,” he said, but would not specify when the agency would announce the winners.

The contracting process is moving ahead despite Congress’s reluctance to fully fund Trump’s pet project and Mexico’s expressed unwillingness to pay for it. Congress has set aside $20 million in the current budget for the prototypes but has not appropriated any other money for the wall.

Trump’s 2018 budget calls for $2.6 billion for “high-priority tactical infrastructure and border security technology.” Of that amount, $1.6 billion is for “bricks and mortar construction” and $1 billion is for infrastructure and technology, such as roads needed to access construction sites and surveillance equipment.

Trump said last week his wall would pay for itself if it were made of solar panels.

“This way, Mexico will have to pay much less money,” Trump said during a rally in Cedar Rapids, Iowa. “A solar wall. It makes sense. Let's see. We are working it out. Solar wall panels.”

Vitiello said the agency is partnering with industry to identify “innovative” ways to build a wall along the border, but said he is unaware of any discussions with the White House about a solar powered wall.

"We’re leaning on industry to innovate and use other materials to show us what they think is possible," he said.

Vitiello acknowledged that there are at least 130 miles along the border where a wall would be impractical, because of natural barriers such as lakes, rivers and a mountain range.  

“There are areas where a wall does not make sense,” he said. “It’s not just about infrastructure, but to have operational control, we also need technology, and more importantly, the officers and agents who are the actual last line of defense of our homeland."

Among the immediate priorities will be replacing 14 miles of fencing in San Diego and 20 miles of vehicle barriers in El Paso, as well as installing 35 new gates in the Rio Grande Valley to cover gaps in the existing border fence.

The prototypes will be built on the eastern edge of the secondary fence in San Diego in proximity to each other, and will act as new barriers, Vitiello said.