Grid Scale, Solar, Storage

PV You Can Drive On: Promising Technology in Solar Roads

The concept of using road surfaces to generate clean solar power is moving beyond the idea stage. Roads absorb heat from the sun every day and are usually free of sightline obstructions that could otherwise block the transmission of light rays. And if the roads built for cars and driving are partly to blame for global warming, why not make them part of the solution too?

Idaho-based Solar Roadways is one of the trailblazers. Electrical engineer Scott Brusaw was inspired to start the company when he heard Caltech solar energy expert Nate Lewis suggest that covering just 1.7 percent of continental U.S. land surface with photovoltaic (PV) solar collectors could produce enough power to meet the nation’s total energy demand.

Brusaw put two and two together when he realized that the interstate highway system already covers about that much of the nation’s land surface, so he got to work designing a system that combines a durable and translucent glass road surface with PV solar collectors that could be wired directly into the electricity grid.

The heart of the solar roadway concept is the solar road panel. Each individual panel consists of three basic layers, the road surface layer, which is translucent and high-strength yet rough enough to provide traction. The surface layer is capable of handling today’s heaviest loads under the worst of conditions and protect the electronics layer beneath it.

three layers of the solar road panel

The three layers (top, middle, and bottom) of a solar road panel.

Next is the electronics layer, which contains a large array of cells, the bulk of which contain solar collecting cells with LEDs for “painting” the road surface. These cells also contain the “Super” or “Ultra” caps that store the sun’s energy for later use. Batteries are not used in the solar roadway. Since each solar road panel manages its own electricity generation, storage, and distribution, they can heat themselves in northern climates to eliminate snow and ice accumulation.

The third layer is the base plate layer, which distributes power (collected from the electronics layer) and data signals (phone, TV, internet, etc.) “downline” to all homes and businesses connected to the solar roadway. The power and data signals are passed through each of the four sides of the base plate layer. The base plate layer is directly attached to vertical risers, pneumatic or hydraulic pistons that raise or lower different points of individual solar road panels. Riser bases are installed beneath the frost line to avoid the “heaving” phenomenon common in colder climates where the ground freezes and thaws. This provides a natural earth ground for the electronics layer of the Solar Road Panels. The risers are controlled (raised, lowered, or locked) by the solar road panel’s microprocessor board. The microprocessor board communicates with each adjacent panel to ensure a seamless road surface.

Brusaw believes his system, if implemented from coast-to-coast in place of the tarmac on existing highways, could produce enough energy to meet the entire world’s electricity needs. But skeptics wonder whether such an expensive high-tech road surface can stand up to the rigors of everyday use-from overloaded 18-wheelers putting extra stress on the highway to oil spills seeping into expensive electronic circuitry-without having to be replaced or repaired often. Brusaw acknowledges that his system still needs fine-tuning, but in the meantime is developing a working prototype along a 45-mile stretch of road between the Idaho cities of Coeur D’Alene and Sandpoint.

This week the company is meeting with professors from the University of Idaho’s civil engineering faculty to discuss the development of the base plate (bottom layer). “U of I has been recognized by the U.S. Department of Transportation as one of the nation’s top transportation research universities,” says Brusaw.

For the top layer, Solar Roadways has approached the nations top materials research labs, “Penn State University’s Materials Research Institute and the University of Dayton’s Research Institute [are] working of figures for developing the top layer,” he says.

After the cost estimates are in, “we’ll be in position to approach our investors for funding. They seem far more interested in the time frame than the money required,” says Brusaw. The company says that it has four interested investors at this time.

“It looks like 2008 is going to be our year. Everything seems to be falling into place at just the right time,” says Brusaw.

Overseas, Europeans are also pioneering ways to use the sun’s rays to work as they beat down on roadways. The British firm Astucia has developed a road stud that contains small solar panels and emits LED light to illuminate dark roadways. On the 120 U.K. roads where the new studs have been installed, night-time accidents are down 70 percent.

And the Dutch firm Ooms Avenhorn Holding BV has developed a way to siphon solar heat from asphalt road surfaces and use it to de-ice roads and help power nearby buildings. A latticework of pipes under the road surface allows water to heat up during warm weather. The water is then pumped deep under ground where it maintains its higher temperatures and can be retrieved months later to keep road surfaces ice-free during winter months. Apartment buildings, industrial parks and an air force base have benefited from the innovation, and the firm is working on exporting its system to other countries in the coming years.

Portions of this article were originally published in EarthTalk, a syndicated column published by “E – The Environmental Magazine” and were reprinted with permission.