Rock to Road

Features
Sunny days ahead

Solar panels part of the future of roadbuilding


February 6, 2020
By Grant Cameron

It’s a workday in the not-too-distant future and roadbuilding crews are putting the top layer on a new highway. In addition to traditional asphalt and concrete, though, they’re installing solar panels on the surface that will absorb sunlight and turn it into electricity which can be transmitted to the grid to power nearby buildings.

Crazy idea, right? Not so fast. The notion of building solar roadways, it seems, might be closer than you think.

While the traditional building materials for roads, sidewalks and cycling paths will still be part of the mix, roads of the future could also include solar panels. Studies are now being conducted and on-site testing is underway to figure out how they might be incorporated into road surfaces to generate electricity.

One of those trials took place at Thompson Rivers University (TRU) in Kamloops, B.C. where a solar compass and walkways, consisting of 64 solar panels, wiring and modules, were installed at the campus. The endeavour was the first of its kind in Canada.

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The surface panels, coated with a proprietary, skid-resistant material made of a transparent layer of glass polymer particles, collect the sunlight and produce about 10,000 kilowatt hours of electricity annually.

The university did the project to evaluate the technology. While the surface doesn’t bear vehicle traffic, it has moved the needle on the idea of solar roads.

Brian Johnson, co-founder and director at Solar Earth Technologies in Vancouver, which donated the solar panels to the TRU project, says he foresees a future when solar sidewalks and roads are a viable alternative.

“In a very short time, we’ll be doing our first solar driveways and, hopefully, sidewalks. We view that as the thin edge of the wedge and as technology improves there will be wider application of what we feel is a real solid alternative.”

Technology is already available that enables solar panels to withstand the wear and tear of traffic, heavy loads and vehicle stops and starts, he says. The holdup is figuring out how to affix them to the road surface.

“Frankly, the problem is getting the things to stick onto the surface. There’s still some challenges for solar roads. The universal challenge is adhesion of the photovoltaic layer to the traditional road bed because there’s often a mixture of aggregates and gravel metres deep and then perhaps asphalt and concrete on top,” he says.

Civil engineers are working on that challenge, though, he explains.

“They’ve been experimenting with line painting and line tape and that sort of stuff, but it’s very difficult to get thin layers to adhere to the traditional road course,” he says. “From the bottom up or the top down, there will be a meeting of those two dimensions and then it will be a question of opportunity cost.”

There are other formidable obstacles, of course, to overcome. For example, the wiring in modules is subject to dampness while storing power is still an issue. And, because the solar panels must be safe in wet and snowy conditions, engineers are still tweaking their recipes for coating the glassy surface of panels with materials that provide good traction in inclement weather.

Another sticky issue is that of dust, dirt or snow. Solar cells in the panels are less efficient and therefore produce less power if they’re obscured by such material.

There is also debate as to whether solar roadways are the best option, as studies have shown that panels on a solar farm provide energy at a lower cost because they are installed at an optimum tilt angle whereas modules on a road surface are horizontal and therefore don’t get direct rays from the sun.

While it may still be early days in the development of solar roads, Johnson firmly believes that they are the way of the future. He says one of the most important lessons learned as a result of the TRU venture is that surface-mounted solar panels can work on roads and highways – even in Canadian winters.

“There are challenges like snow removal, chemical de-icing, temperature fluctuations in surface temperature, ground moisture and drainage,” he says. “The biggest lesson was that it works and let’s just move forward.”

Johnson maintains there’s a compelling business case for adopting solar for roads and other types of urban transportation infrastructure and has faith that engineers will figure out ways to make the technology feasible.

“We believe that the solution will likely be a pre-cast, perhaps initially in concrete, with a very durable top layer,” he says. “It will probably be modularly manufactured and installed. But it’s clear that what is currently being used on sidewalks for pedestrian applications will actively change for the true solar roads to be built.”

Meng Wang, founder and executive chairman of Solar Earth, maintains the technology is destined to eventually be adopted because once solar roads are installed they keep generating power at little to no cost. The project at TRU, he says, has proven that the technology has advanced to the point where it can be successfully used on roads and highways.

Wang can’t reveal the specific makeup of the friction or traction surface coating for the panels developed by Solar Earth, but says it is a combination of binding and aggregate materials which also help uniformly distribute pressure across the surface of the panels. Different mixes are still being developed for varied situations and temperature fluctuations and the company continues to tinker with its products.

“The module itself is also proprietary,” notes Wang. “It’s encapsulated using special thin films – up to 10 different layers – that allow for heavy loads to be driven on top of it. So, the surface can last in different environments.”

TRU was chosen as a pilot project to test out the solar panels after a government officer connected Wang to geography and environmental studies professor Michael Mehta who was keen on such ventures. The university already had solar panels installed on campus buildings, rooftops and windows, so it made sense to do a pilot that further tested the worthiness of the technology for road surfaces.

“The only thing missing was the roads at that time, so that’s how we started,” says Wang.

Solar Earth is now building systems for walkways, driveways, patios, roofs and roadways, and has products that can be mounted directly on flat concrete or on interface layers. The company recently won a municipally-tendered contract to build a solar sidewalk at an intersection in Tampa Bay, Fla. The project is scheduled to begin in April. Power generated by the sidewalk will supply electricity at the intersection.

While the pilot at TRU has helped push the envelope on the issue in Canada, experiments with solar panel walkways and roadways have been tried or are underway in other parts of the world. Results have varied.

In 2016, for example, a pilot consisting of 30 solar panels and sensors was installed by Solar Roadways in a 150-square-foot section of pavement in Sandpoint, Idaho. The tiles generated power, which was fed into the electricity grid. However, it was shut down two years later after problems started to emerge.

That same year, a one-kilometre trial solar road consisting of 3,000 square metres of photovoltaic panels was installed near Tourouvre, France. However, cracks appeared in part of the road and it had to later be demolished due to damage from wear and tear. The thoroughfare, meanwhile, was only producing half of the expected energy because engineers didn’t take into account leaves falling on the road.

A year later, China opened a one-kilometre-long road in Jinan City, south of Beijing. The two-lane road has 5,875 square metres of photovoltaic panels and a protective surface layer made of transparent concrete, which can reportedly handle 10 times the pressure of standard asphalt. Beneath the concrete are solar panels and under those is an insulating layer designed to protect them from ground dampness.

A 29-kilometre test stretch of solar roadway was also installed near the Alabama and Georgia border in the U.S. and powers the Georgia Visitor Information Centre adjacent to the project.

Meanwhile, in Budapest, Hungary, a 4.6-kilometre stretch of sidewalk with solar panels provides power to charge electric vehicles and a nearby office building.

A 70-metre bike lane covered with solar panels in Krommenie, The Netherlands, also provides enough electricity to power three houses.

Solar roads may not be a mainstream part of roadbuilding today, but there is definitely interest in them being part of the solution for meeting the global energy demands of tomorrow.