By Claude Goguen, P.E., LEED AP
Solar technology isn’t new. Evidence suggests humans used magnifying glass in the 7th century B.C. to create fire from the sun’s rays. In 1767, noted Swiss physicist and adventurer Horace-Bénédict de Sassure invented a solar oven using a well-insulated box with three layers of glass to trap thermal radiation. Another milestone occurred in 1954, when scientists at Bell Labs developed the silicon photovoltaic cell, the first solar cell capable of converting the sun’s energy into enough power to run common electrical equipment. Today, you can simply walk into your local hardware store and buy a residential solar power system.
Looking ahead, great potential remains for groundbreaking solar power technologies. And with the help of precast concrete, inventors are paving new roads to success.
Solar roads in the U.S.
Imagine a parking lot that’s roughly the size of South Carolina. That’s what you’d get if you combined the roughly 30,000 square miles of roads, parking lots, driveways, playgrounds, bike paths and sidewalks in the contiguous U.S. Scott Brusaw, an electrical engineer and Marine Corps veteran, hopes to take that surface area and use it to convert the sun’s rays into energy. Solar Roadways, a technology he and his wife Julie developed together, will power this process.
As a child, Scott envisioned the creation of an “electric road.” Throughout his career, which included everything from a stint in the oil exploration industry to research and development work, he continued to refine his idea. Today, Scott and Julie function as co-founders of their ambitious project, which has garnered much attention from a variety of major media outlets.
The technology consists of hexagonal structural pavement panels protected by textured glass. An integrated circuit controls each unit, which also contains LED lighting for road lines and signage. Panels convert solar radiation to electricity and can be mounted in new or existing roadways. The Brusaws have received support from many parties, including the Federal Highway Administration, which has funded two study phases of the Solar Roadways system.
In Phase 1, FHWA confirmed the functionality of the system’s electronics. The Brusaws built a prototype crosswalk panel that included load cells for detecting weight on its surface. When weight is present, data is sent to the solar panel, which then displays instructions for approaching motorists to slow down using LED lights. This process demonstrated the ability of the road panels to communicate with one another.
For Phase 2, Solar Roadways installed a 36-foot-long, 12-foot-wide prototype outside its facility in Sandpoint, Idaho. The parking lot was slanted at a 3% grade to simulate a roadway and was fully functional with solar cells, LED lighting with added colors, heating elements and textured glass. The glass surface was sent to engineers to test for loading, traction and impact resistance. According to Scott, the glass exceeded all expectations, with tests revealing that it could support the weight of a 250,000-pound truck.
In this phase, the panels were placed in a concrete foundation. A concrete stormwater basin and utility corridor were also added to the side of the parking lot. In the real world, the basin would be used to collect stormwater runoff and direct it to appropriate treatment systems. The utility corridors would route cables for electricity generated from the solar cells and could also be used by other utilities. The parking lot is roughly equal to a 3,600-watt solar array.
An ideal material
For the prototype used in Phase 2 of the FHWA study, Scott used cast-in-place concrete. But he sees many benefits in using precast in the future.
“Precast concrete would be ideal for this system,” he said. “The conduits could be pre-installed during manufacturing. Also, we had to drill the concrete to be able to install 396 bolts for the Phase 2 prototype. Precast panels could have those anchors pre-installed.”
Precast panels could also quickly and easily be delivered to the installation site. Then, the solar panels would bolt into them, completing the connection.
The Brusaws’ vision is for Solar Roadways to first take root in smaller projects, including driveways, bike paths and sidewalks. From there, parking lots and residential roads would follow, with the ultimate conversion being the nation’s highways. To get to that point, Solar Roadways must next conduct large-scale tests in parking lots or other surfaces that would not impede traffic. The Brusaws are also experimenting with piezoelectric elements and thermocouplers for their next design. Both of these devices can produce energy around the clock.
The Brusaws may be dreamers, but they’re not the only ones. Across the Atlantic, another company is exploring a similar technology and has progressed to larger-scale field testing.
Just a few miles outside of Amsterdam in the town of Krommenie, a 230-foot-long by 11.5-foot-wide bike path dubbed “SolaRoad” is attracting international attention. Constructed in October 2014, the path represents an important project exploring the use of road surface to collect solar radiation and convert it to electricity. Precast concrete panels with a translucent top layer of tempered glass are used. Crystalline silicon solar cells are located under this glass.
In 2009, Netherlands-based organization TNO came up with the vision for the path and later formed a public-private consortium with other outfits – including the North Holland government, Ooms Civiel and Imtech – to bring the vision to reality. Like Solar Roadways, the ultimate goal is to have large parts of the road surface in the Netherlands act as a solar panel. The generated electricity could then be used for street lighting, traffic systems, households and electric vehicles.
Sten de Wit, spokesperson for SolaRoad, believes that – with time – the system could have a significant positive impact.
“This could be a breakthrough in the field of sustainable energy supply,” he said. “In particular if the road concept will develop into a system with which the generated electricity is transported to the vehicles driving on the road. Subsequently, a big step towards an energy-neutral mobility system will be possible.”
SolaRoad is being developed in stages. After a feasibility study, a first prototype was created in 2010 and has been tested extensively in the laboratory. The results raised questions and revealed some points for improvement, but were so promising that in 2011 it was decided to further develop the system. This is what led to the bicycle path in Krommenie.
Throughout the course of the project, alternative options have been examined for both the solar cells and the glass. Researchers are looking for the best skid-resistant coating to use on the glass to provide adequate braking traction. The glass was also tested for fatigue and loading.
SolaRoad has exceeded expectations since it first opened to the public. In the first six months, the bike path had already generated 3,000 kilowatt-hours, enough energy to provide a single-person household with electricity for a full year.
Stan Klerks, SolaRoad lead engineer, said that using precast concrete panels contributed to the success of this project. “We learned it’s possible to integrate things in precast concrete elements,” he said. “The panels were simple to install and had conduits already integrated for cabling.”
SolaRoad already has plans to extend the prototype next year to 330 feet in length, which would produce enough electricity to power three houses. As the system continues to evolve, one main area of focus will be refining the technology to lower costs, making SolaRoad available for larger-scale projects.
The natural choice
Precast concrete played a role in solar power generation long before the development of Solar Roadways and SolaRoad. Footings and piers are widely used to provide a stable support system for solar modules. Precast has also been integral in the sustainable construction and repair of roadway systems. With its many advantages and sustainable benefits, precast concrete is the natural choice for any roadway solar system project.
For more questions on precast applications such as this or any other sustainable project, please contact Claude Goguen, NPCA’s director of sustainability and technical education, at (317) 571-9500 or by emailing [email protected]
Claude Goguen, P.E., LEED AP, is NPCA’s director of sustainability and technical education.