— -- Customs and Border Protection (CBP), the agency implementing the border wall construction process, is planning for the construction of four to eight wall prototypes in San Diego "later this summer," said CBP Acting Deputy Commissioner Ronald Vitiello Tuesday.
"We're leaning on industry to innovate and to use other materials to show us what they think is possible, doable and innovative for this purpose," said Vitiello.
CBP has entered "phase two" of the process, and is currently reviewing and evaluating proposals for wall prototypes, but no contracts have been awarded yet. On March 17, CBP issued two separate requests for proposals from companies for wall prototypes -- one for "reinforced concrete" and one for "alternative materials."
"Although this acquisition is still underway, we plan to start building the prototypes in San Diego later this summer," said Vitiello.
A CBP draft briefing to Congress had previously stated June as an intended start date for prototype construction, but in recent weeks the Department of Homeland Security, which oversees CBP, has said "summer."
Vitiello said that at this time it's "hard to nail down” an exact date to start construction.
President Donald Trump's January executive order on border security called for the "immediate construction of a physical wall on the southern border," a goal that the president reiterated throughout his campaign.
"Any and all prototypes will be designed to deter illegal entry into the United States,” said Vitiello said.
Last week, Trump touted a solar-paneled border wall before a campaign crowd in Iowa, calling it “my idea.”
"And we're thinking of something that's unique. We're talking about the southern border, lots of sun, lots of heat. We're thinking about building the wall as a solar wall so it creates energy and pays for itself,” Trump said to the cheering audience.
However, back in April when Department of Homeland Security was reviewing bids for the wall project, at least one contractor, Gleason Partners LLC of Las Vegas, submitted a plan to use solar panels to cover sections of the wall.
Vitiello said that he was "not aware" of any discussions with the White House about solar panels before the president’s remarks.
The president's statement, "hasn’t impacted the planning in it of itself," said Vitiello, who pointed out that there are two distinct proposals, one for concrete and one for "not-concrete," so CBP expected "to have some innovation."
"We're leaning on industry to innovate and to use other materials to show us what they think is possible, doable and innovative for this purpose,” said Vitiello.
At the time the request for proposals went out, some of the companies put plans on their own websites, so CBP was aware that there were people out there that were thinking about a "wall that has solar panels on it," said Vitiello.
CBP is prevented from sharing information on the companies bidding for the wall project because of federal procurement rules.
Vitiello described the number of total bidders as "a substantial group," but said he did not know the specific number.
"We are looking at [the] end to have somewhere between four and eight of these prototypes," he said.
The primary purpose of this effort is to come up with "design standards" for the border wall that may be constructed along the southwest border, according to CBP.
The completion of the prototypes' construction is expected within 30 days of the issuance of notice to proceed, and final selection will take place after a "thorough review and evaluation."
For fiscal year 2017, Congress is providing funding for replacement of 14 miles of primary barrier in San Diego, two miles in El Centro, 20 miles of vehicle barrier in El Paso, 4 miles of pedestrian barrier in El Paso and 35 new gates in the Rio Grande Valley area.
Rio Grande Valley has been an area of exploitation and an area lacking in border infrastructure, according to Vitiello.
For fiscal year 2018, CBP has prioritized 28 miles of new levee wall and 32 new miles of border wall in the Rio Grande Valley region, as well as 14 miles of replacement secondary wall in San Diego.
The section of the San Diego wall that CBP has identified for replacement has been breached "800 times in the last year," Vitiello said.
CBP has identified approximately 130 miles of border where a wall doesn't make sense to build, like areas with lakes, high mountains or other natural physical barriers.
However, the agency said its prepared to make changes to its priorities as conditions on the ground evolve.
The prototypes, which will primarily serve as a design evaluation for the agency, will also create a new barrier in San Diego that did not previously exist. That area was chosen by CBP because it's government-owned property, is well-known to agents on the ground, and it already has the roadways, lighting and sensor material that will need to be incorporated into design plans.
Trump has said that he will get Mexico to pay the U.S. back for the wall construction.
However, on Tuesday, Vitiello, said that he was "not aware" of any offers of financial help from Mexico for the border wall.
ABC News' Justin Fishel contributed to this story.