Ever since Scott and Julie Brusaw went public with their idea for building solar-powered LED roadways, they've faced a constant barrage of skepticism and even outright hostility.

The reaction was expected given how technically difficult it would be to execute their vision of electrifying roads and highways with reinforced solar panels. Some questioned whether the application for solar is even necessary. 

But one organization -- the most important agency governing America's roads -- was willing to give them a shot at proving the concept.

In 2009, after a couple years of tinkering in their driveway, the Brusaws secured a $100,000 grant from the Department of Transportation for their company, Solar Roadways. The grant was supposed to be used for gathering information from engineering experts in a variety of fields and developing a concept paper based on the findings.

"I didn't need that much money to have a bunch of professors write a paper. So I asked [the DOT] if we could simply build a prototype," said Scott Brusaw.

In February 2010, the Brusaws built their first panels, a 12-foot by 12-foot array without solar cells, to test whether the underlying electronics would work.

That year, Solar Roadways won a $50,000 community award through GE's Ecomagination challenge, giving it another pool of money to keep experimenting.

Then, in 2011, the DOT followed up its initial support with a $750,000 grant to assist Solar Roadways in developing a second "parking lot" demonstration array with solar cells, LED lights, and a heating system built in.

An up-close image of the prototype solar roadway panels with heating elements and LEDs built in. Photo credit: Solar Roadways.

The DOT's role wasn't just to hand out money. The department also helped test the arrays to figure out if they were actually safe, functional and able to withstand punishing road conditions.

Eric Weaver, a research engineer at the Federal Highway Administration's research and technology arm, took the lead on the testing. When asked what he thought of the plan to blanket America's roads with solar panels and LED lights after years of evaluating the concept, Weaver was blunt: "I'd say it's not very realistic to cover the entire highway system with these panels."

But Weaver was also quick to qualify his statement. "If you don't reach for something, you'll never get there. Just the effort of doing something new creates byproducts," he said.

Earlier this year, Scott Brusaw, himself an electrical engineer, decided he needed more financial resources beyond government grants in order to hire full-time materials experts and civil engineers to prove the concept. So Solar Roadways started an Indiegogo crowdfunding campaign and created a hyped-up video to woo potential donors.

“We can’t say that it would be safe for roadway vehicular traffic.” Eric Weaver, Department of Transportation

The campaign was wildly successful, bringing in $2.2 million for Solar Roadways. The reaction to the fundraise ranged from incredulity to loathing. Some were convinced it was an outright scam

In an interview with Greentech Media, the DOT has opened up about the Solar Roadways testing process for the first time. Although the company made radical claims about the technology's potential in its Indiegogo video, Solar Roadways is not a "scam." The Brusaws continue to work on the technology with engineers from universities, and the product has gone through real-world testing with actual early-stage products to show for it.

But as DOT's Eric Weaver explained, it is very, very far from being proven as envisioned.

The biggest unknown is safety. Driving or walking on a textured glass surface is completely different than asphalt, which is designed specifically to increase traction. Weaver said that the DOT needs to go through more rounds of testing before it can weigh in.

"We can’t say that it would be safe for roadway vehicular traffic," said Weaver. "Further field-traffic evaluation is needed to determine safety and durability performance."

Solar Roadways says it has tested its wet textured glass surface at a university lab and has shown that it can stop a vehicle going 80 miles per hour within the required distance. However, getting approval from a university lab is much different from getting it from federal highway authorities.

Durability is also not fully proven, said Weaver. The DOT uses a weight deflectometer to test impact loads up to 16,000 pounds. But the department was not able to get its equipment up to Solar Roadways' testing headquarters (i.e., Scott and Julie's home) in northern Idaho. So they instead used a 3-D modeling analysis. 

"We have no idea how it would hold up to wear under foot or car traffic," said Weaver. 

Scott Brusaw drives a tractor over the prototype parking lot. This does not qualify as an official DOT test. Photo credit: Solar Roadways

Brusaw said he plans on taking up a new round of testing with universities or the DOT in order to get better simulations. Solar Roadways has an option to continue its relationship with the federal government for a third phase, or it could use some of the Indiegogo money to find additional methods of testing.

The third limitation, said Weaver, was materials and equipment availability. Finding large circuits to put under the glass was very difficult since every company has worked to make circuits smaller, not bigger. 

"They spent a lot of time trying to get the circuitry embedded in the glass. But issues with the prototype could be overcome with larger-scale automated production," said Weaver.

Brusaw admitted to supply challenges, but said many of them had been overcome. 

"It wasn't necessarily a scarcity of materials; it was suppliers promising things they couldn't deliver," he said. 

In one instance, it took two extra months to get plastics for the internal support structure because the supplier didn't have access to a dye color that it had suggested to Solar Roadways in the first place. In another, the winning bidder for the circuits only told the Brusaws afterward that its equipment couldn't support such large boards. 

The circuits themselves are now broken down into four sections for easier manufacturing and then assembled onsite. "Anyone can do those four sections," said Brusaw. He said that LED lights have been the easiest thing to supply thus far.

There's one other very important technical detail that hasn't been officially verified: the performance of the solar cells themselves.

Brusaw has been comparing the embedded solar cells flat on the ground to conventional rooftop panels angled toward the sun. What he found surprised him: "We were within 5 percent of theoretical values."

Those results, monitored using Enphase microinverters, have not been independently verified. All the testing has been done onsite at the Brusaws' home, so it's hard to say exactly how the solar component of the road will perform over time. 

“I need some more people under my roof. I want to put them in a room and figure out how to make it work.” Scott Brusaw, Solar Roadways

So with years of testing now done, is it possible to say whether Solar Roadways' long-term vision of paving highways and roads with solar actually makes sense? 

Weaver said the DOT isn't even close to saying if it could be used for high-impact environments. But he did not dismiss the concept entirely.

"I believe the application can be used for smaller scale purposes -- potentially, pedestrian walkways and sidewalks that get lower load and have fewer safety considerations," he said. "For roads, there are so many unknowns."

Even if the DOT fully backed the technical possibility of swapping out pavement for solar panels and LEDs, the business case is still undeveloped.

"We haven't done the cost analysis just yet," admitted Brusaw, directly contradicting the claim in the company's promotional video that the panels "pay for themselves" by producing their own electricity.

He did say that Solar Roadways would not permit, install or service the paneling. The company would simply be a manufacturer and let service providers or governments figure out how to finance and build projects. Forget the current technical limitations; navigating the complicated network of private, state and federal rules for transportation planning would also be a major headache.

Brusaw has a couple short-term applications he's working on to get beyond the prototype phase.

The first is a project in downtown Sandpoint, Idaho, near where the inventors reside. The goal is to develop five pilot projects on non-critical applications such as downtown sidewalks, a train station and part of an airport tarmac. All the year-round data about performance will be streamed to the public for monitoring. The second application could be on tribal lands, which have their own rules governing roads. Brusaw envisions installing a parking-lot scale project at a casino, or outfitting a small residential road on a reservation.

At this point, the only solar "roadway" is a 12-foot by 36-foot grouping of panels in a barn in Idaho that is being driven over by tractors on a regular basis. It is not anywhere close to being suitable for real driving applications -- not now, and perhaps not ever.

Brusaw said the next step will be to hire more engineers full time with the new crowdsourced funds, supplanting the part-time graduate students that have been helping him and Julie. "I need some more people under my roof. I want to put them in a room and figure out how to make it work."

But Eric Weaver, who witnessed firsthand the limitations of the technology over years of testing, can't bring himself to side with the hardcore skeptics. He's open to the possibility that something will come of it.

"In terms of the long-term vision, I don’t consider it to be realistic. But I enjoy the vision and appreciate it, and will try to support them to see what other benefits may present themselves," said Weaver.

In the meantime, a lot of eager armchair investors who donated to the company will have a long time to wait before knowing if anything will ever come of their investment.