Take a solar panel. Surround it with light-emitting diodes attached to a microprocessor and, in northern climes at least, some kind of heater. Sheath all of that with the 100-year-old technology known as tempered glass. Voila: the basic building block of what has been dubbed by its creators, electrical engineer Scott Brusaw and his wife Julie, a solar roadway. It could one day make for a highway built of 0.4 –square-meter hexagonal panels, a hodge podge of green circuit boards surrounding 36-watts worth of blue solar panels, all covered in thick, bumpy glass for safety and traction.

The idea is to put unused roadway to good use (generating electricity) while also providing an electronic means for lane shifts, driver messages and other utilities. Bonus: solar roadways obviate the need for an electric grid by including a "Cable Corridor" right in the side of the roadway that eliminates the need for power lines running alongside it. And if outfitted with sensors as well the solar highway could transmit real time traffic data or other information of interest. The novel idea has been around for a few years now, bursting back into prominence this summer thanks to a new crowdfunding campaign to support further research and development that garnered $2.2 million before closing on June 20.

The solar roadway already exists, or at least an 11-meter-long solar parking lot outside the Brusaw backyard lab in Idaho made up of 108 of the prototype panels. That's the equivalent of a 3.6 kilowatt solar array, capable of producing roughly 14 kilowatt-hours of electricity per day, or roughly half the electricity use of a typical U.S. home.

As this prototype demonstrates, the Brusaws don't have to start with roads—patios, parking lots or sidewalks, among other currently paved surfaces, might make for a more feasible starting point. But, in the long run, the vision is to take the continental U.S.'s roughly 75,000 square kilometers of road and turn it into a massive solar farm to replace the nation's need for fossil fuel-fired power plants, thus solving climate change and energy security issues in one go. Even better, the solar roadways pair nicely with the need of electric cars for ubiquitous charging wherever the vehicles may go.

The Brusaw's hometown of Sandpoint, Idaho and surrounding communities have already signed up to host future prototypes on sidewalks, parking lots, airport tarmacs, even train station passenger platforms. The goal of such testing is to prove that such panels can last for 20 years while supporting weights of more than 100,000 kilograms.

There are, however, a few challenges to overcome. What happens to the solar roads at night or on a cloudy day, when the PV is not generating electricity to power homes or cities? The Brusaws' answer is to draw power from the grid, presumably from flexible generators, such as natural gas-burning combined cycle turbines or hydropower projects with the room to store water for a dark night (though Brusaw told me he expects wind turbines to fill this role back in 2009. He did not respond to repeated requests for an interview this time around.) As presently designed, the LEDs and heating elements are disconnected from the photovoltaics, meaning these elements require electricity from the grid 24/7. The heaters alone require more power than the available PV in the hexagon can supply.

Then there's the materials challenge posed by the novel use of glass. This glass must be tempered, self-cleaning, and capable of transmitting light to the PV below under trying conditions, among other characteristics—a type of glass that does not yet exist. And that's just the glass. There's the additional challenges posed by putting together photovoltaics, LEDs and other components, not unlike a smartphone but one that will be run over by trucks.

Finally, there's the problem that these 50 United States barely maintain asphalt roads, crumbling highways and unafe overpasses and bridges as it is. U.S. roads are essentially run to failure (i.e. as poorly maintained as possible) so how will any city, state or federal government pay any amount more to put in a solar road rather than paving with asphalt? It's not just that the panel is more expensive than pavement, it's the additional expense of maintenance, replacing the inevitable defects and generally tending a technological jumble subjected to the brutal pounding of daily traffic and weather, among other stresses.

Of course, that pounding can also be put to use via the piezoelectric effect. But that's a whole 'nother yellow brick roadway—and a technology that the Brusaws are also considering incorporating into their solar road panel.

Credit: All images courtesy of Solar Roadways