A New Look At The Viability Of Solar Roads

Please welcome back Ellie Gabel to the 21st Century Tech Blog. From childhood, she fell in love with science by reading magazines covering everything from astronomy to zoology. She is a big fan of Richard Dawkins. You can find more of her writing on her website.

In this, her third contribution, she writes about a subject that has appeared in postings on this site before, the viability of developing embedded solar power in roadways. Let us know what you think by sending your comments.

What if the global road system had untapped potential to produce clean energy? The latest renewable energy innovation may be designing solar technologies to fit into existing transportation infrastructure. While previous testing has underscored several barriers to implementation, experimentation has many wondering if solar roads could solve the world’s growing energy demand.

A Viable Solution or Fantasy: What Are Solar Roads?

Solar roadways are exactly what they sound like, solar panels embedded into the surface of streets and highways converting sunlight into clean electricity. Solar roads have three layers: durable, textured glass for tire-gripping, PV panels similar to rooftop systems, and a base plate for energy distribution. 

Across the United States, there are 6.6 million to 6.75 million kilometres (4.1 million to 4.2 million miles) of public roads, 70% of which are rural. Currently, solar roads are not a working solution but several startups are exploring how to make clean energy-producing streets viable.

Many are skeptical because previous attempts to implement solar roads have produced unfavourable outcomes. Aside from issues with wear and tear, how much electricity could solar roadways generate with shade from heavy traffic and debris? Maintenance and safety remain significant impediments. 

Potential Benefits of Solar-Powered Roadways 

The solar energy market has risen dramatically over the last decade as the solar photovoltaics (PV) field grows and federal and state incentives make rooftop panels more affordable. With an emphasis on renewable energy sources to power the built environment, it’s little surprise solar is being explored for other purposes.

The development of solar-powered roadways remains, at best, hypothetical. However, according to Idaho-based company Solar Roadways, integrating solar energy into existing pavement has the potential to do the following:

• Produce three times more electricity than the annual energy consumption
• Deliver inductive charging, allowing electric vehicles to receive a charge just by driving over them
• Incorporate light-emitting diode bulbs to illuminate dark streets
• Integrate a heating feature to melt snow and ice on surfaces

Solar-panelled roads wouldn’t necessarily send electricity to the energy grid. Likely the power the roads produced would be used for roadway infrastructure: highway lighting and signage, powering traffic lights and providing energy for emergency equipment.

A Path Forward: Solar Roads in Action

The first attempt at a solar road was the Wattway in France in 2016. It failed. Nevertheless, global startups have continued exploring the possibility of solar roadways in the future including work being done in the United States and the Netherlands. 

United States

The state of Georgia has initiated a testing site in Peachtree Corners, Georgia along a 29-kilometre (18-mile) stretch of Interstate 85. It is currently the only functioning solar roadway in the United States. The PV panels have been installed on the highway surface and produce power for streetlights, traffic systems and electric vehicle infrastructure.

Georgia’s solar roadway project is backed by the Colas Group, the same company behind France’s Wattway solar road and hoping to learn from that unsuccessful first attempt. What Wattway showed is that solar roads produce less energy than Colas initially thought because heavy traffic, weather conditions and ongoing wear hindered panel efficiency.

Another Solar Roadways pilot project in Sandpoint, Idaho faced significant issues.

Netherlands

The Colas Group has started Wattway solar cycle paths in the Netherlands. The cycle paths span 35,000 kilometres (21,748 miles) and create clean energy from areas otherwise requiring excessive land use for utility-scale solar.

The solar panels’ widths are only a few millimetres. They are coated in resins and polymers to give them a similar grip to conventional streets. Their composition allows them to absorb enough sunlight and resist cyclists’ weight. 

Comparing Solar to Piezoelectric Roadways

Solar roads use PV panels to convert sunlight into energy. Piezoelectric technology uses mechanical energy from the weight of cars driving over special-made tiles embedded in a road’s surface.

French physicists Jacques and Pierre Curie discovered piezoelectricity in 1880 after identifying a mechanical and electrical response of ceramics and crystals. The crystals generated electrical voltages in proportion to an applied force. The brothers discovered that a crystal’s charge balance must endure a 10% impact to generate electricity. 

The ability of quartz crystals to convert mechanical energy into electrical energy became known as the positive piezoelectric effect. Since then, numerous industries have utilized crystalline materials for wide-ranging applications. On roadways, crystallized ceramic tiles harvest electricity from vehicle pressure and speed.

Israel-based Innowattech was the first to develop piezoelectric technology for the road in 2008. Its findings indicated that when truck traffic in one lane exceeded 500 vehicles per hour, the road vibrations generated 250 kilowatts of electricity per kilometre, which could power 400-600 homes. Similar field studies have been conducted in the U.S. and China, but test data on road piezoelectricity’s success remains insufficient.

Vibrational technology and roadway solar could complement each other, boosting energy generation. However, significant investments in research and development are needed to ensure this approach is pragmatic, hardwearing and efficient in real-world applications.

Challenges and Considerations

Implementing solar roads faces numerous challenges. The financial constraints alone could end future deployment. Solar Roadways estimated the cost to replace existing roads with its solar roadway prototype at $56 trillion to cover all the roads in the United States. A 2016 Stanford University paper came up with a different estimate of $7.35 trillion based on looking at installation on Interstate highways. At the low end, the per square metre cost of solar roadways works out to $101.42 ($9.44 per square foot) compared to $10.76 to $21.52 per square metre ($1 to $2 per square foot) for traditional asphalt. If that does not impede the technology than what does?

Are Solar Roads Too Good to Be True?

Solar-powered roadways has sounded like a good idea but implementation has shown it is not an easy row to hoe. However, as the world witnesses the rapid transition to electrification, the evolution of solar power, ongoing research and technological developments may present solutions in the future that work.

What’s needed to make solar roadways a future reality?

• Improved materials for better safety, durability and conversion efficiency.
• PVs designed specifically to work in multiple road modalities.
• Integration with smart city infrastructure, energy storage solutions and autonomous vehicle technology.
• Dramatic unit cost reductions with designs that are easy to install and maintain.

An alternate strategy would be to abandon the idea of embedding PVs in roadway surfaces and instead install conventional PV panels along the medians and shoulders of roadway rights of way. This could be implemented at a fraction of the cost.