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 programmes 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 programmes without appropriate internal oversight."
Vitiello said 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' reluctance to fully fund Trump's pet project and Mexico's expressed unwillingness to pay for it.
Congress has set aside US$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 US$2.6b for "high-priority tactical infrastructure and border security technology". Of that amount, US$1.6b is for "bricks and mortar construction" and US$1b is for infrastructure and technology, such as roads needed to access construction sites and surveillance equipment.
Trump said last week that 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."
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 are leaning on industry to innovate and use other materials to show us what they think is possible and doable for this purpose," he said.
Vitiello acknowledged that there are at least 210km 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. "This is not just about infrastructure. To have operational control, we also need technology."
Among the immediate priorities will be replacing 22km of fencing in San Diego, 32km of vehicle barriers in El Paso, and installing 35 new gates in the Rio Grande Valley.
The prototypes will be built on the eastern edge of the secondary fence in San Diego in close proximity to each other, and will act as new barriers, Vitiello said.
