Weight Limits

Hardness

The scale to measure the hardness of materials is called the Mohs hardness scale. It refers to the resistance of a material to being scratched. It lists materials from the softest to the hardest e.g., on a 1 to 10 scale, with talc earning a 1 and diamond, (the hardest common material) being 10.

Asphalt has a hardness of 1.3, copper has a hardness of 3, iron and nickel have a hardness of 4, and steel falls between 4 and 4.5. As you move up the scale closer to diamond, you finally come to glass, which has a hardness of 5.5-6.0.

Strength

When glass is tempered it becomes four to five times stronger than the non-tempered annealed glass listed in Mohs hardness scale. Tempering does not make the glass harder – just stronger. Bulletproof and bomb (blast) resistant glass is made with tempered glass. Solar Roadway® Panels are manufactured in a similar manner. Tempered glass is less likely to experience a thermal break.

Texture/Traction

One of the many technical specs required for SR panels is for a glass surface textured to provide the same or greater traction than current asphalt roads offer (at a minimum) – even in the rain. A variety of textures were tested with a British Pendulum Skid Resistance Tester. Some did not provide enough traction, and one had such an aggressive texture it broke off a piece of the tester. The SR2 texture used was a midrange texture. The final testing results showed the texture was sufficient to stop a vehicle going 80mph (129kph) on a wet surface in the required distance. The test results apply to motorcycles and bicycles as well. New textures will be tested, and the long term goal is to have a whole catalog of textures available to perfectly match each application. For example, highways will require the most robust texture. Applications that are primarily used by pedestrians such as sidewalks and plazas will want a less aggressive texture. For our current SR4 panels, we are using a texture that was designed for pool decks – for wet, bare feet. It’s working well at our pedestrian pilot site.

Longevity and Durability

Repair/ Replacing Damaged Panels

Since the Solar Roadways® system is modular, repair will be much quicker and easier than the current maintenance system for asphalt roads. In the U.S. the time Americans spend idling in traffic costs the nation in a variety of ways.

From the American Automobile Association:
“While many Americans experience congestion on a daily basis, few realize that every hour of congestion, delay, and lack of reliability adds a cost to most services and goods produced or consumed in America.”

Apparently the problem is becoming more serious over time. The new 2019 Urban Mobility Report states that:

“ In 2017, congestion caused urban Americans to travel an extra 8.8 billion hours and purchase an extra 3.3 billion gallons of fuel for a congestion cost of $179 billion.“

They go on to report on the value of data collection: “Better data can play a valuable role in all of the analyses.  Advancements in volume collection, travel speed data and origin to destination travel paths for people and freight allow transportation agencies at all government levels and the private sector to better identify existing chokepoints, possible alternatives and growth patterns.  The solution begins with better understanding of the challenges, problems, possibilities and opportunities – where, when, how and how often mobility problems occur – and moves into similar questions about solutions – where, when, and how mobility can be improved.”

The intelligent Solar Road Panels have the capacity to collect massive amounts of data which can be useful to those working to tackle such transportation problems.

Each of the SR panels contain their own microprocessor, which communicates wirelessly with surrounding panels. If one of them should become damaged it would stop communicating, and the surrounding panels can report the problem. For instance, “I-95 mile marker 114.3 northbound lane, third panel in, panel number A013C419 not responding”.

The panels are light enough that a single operator could load a functioning panel into his/her truck and take it to the location of the damaged panel. The panel could be swapped out and reprogrammed in a few minutes. The damaged panel would then be returned to a repair center.

Potholes are a major source of repair need for asphalt roads and the repair is not nearly as quick or efficient. Potholes in asphalt are formed when moisture accumulates in cracks and breaks in the structure of the asphalt. Temperature fluctuations leading to freezing and thawing then cause expansion and contraction of the material, causing it to weaken. The weight of vehicles contributes to the problem further and eventually a pothole forms. This process cannot happen with SR panels since they are completely impervious to water and therefore potholes will become a thing of the past.

Potholes and other types of road damage can be a danger to drivers, motorcyclists, cyclists, pedestrians, and vehicles. Sometimes potholes are disguised when covered with a puddle of water or ice. Sudden potholes can startle drivers. Some may try to swerve to miss them, which can lead to accidents.

AAA has discussed damages that potholes can do to vehicles. They report that hitting a pothole can knock wheels out of alignment, which then affects steering. A hard impact can dislodge wheel weights, damage tires and wheels, and even suspension components. More about potholes from AAA can be found here.

Hills/Curves/Crowns

People may wonder how SR panels can be installed on hills and curves and how they can accommodate the typical 3% crown that roads have. The very first SR prototype was 12ft x 12ft – it was quickly realized that that size would have made such sites difficult to tackle.

Two important changes were made. The panels were shrunk to about 4ft² and the shape was changed to hexagons, partially because it was apparent that those changes would make installing on hills and curves so much easier. Roads have what are known as “crowns”: the middle of the road is the highest point so that stormwater doesn’t puddle, but instead runs off of the road. The hexagons easily cover this gentle 3-percent slope.

Eventually, it’s expected that a variety of shapes and sizes will be added to the Solar Roadways® catalog, offering even greater flexibility.

Cleaning

There is also a concern how much a layer of dirt would interfere with solar gain if it did not wash off.
A unique test was conducted during summer drought conditions when the surroundings were covered in dirt/dust. There are two identical traditional (not SR) solar panels positioned on the roof of the original SR lab. For the experiment, only one of them was kept clean and then the outputs were compared.

After one of the panels was cleaned, their performance was monitored throughout a sunny summer day. The clean panel only produced 9% more power than the dirt covered panel. Worst case senario, if it is determined that it is difficult to keep the panels clean, it may only result in a small energy loss. Another consideration is that SR panels, being on the ground, are much easier for homeowners to clean than rooftop panels.

Some anecdotal data was collected with the prototype parking lot: a rubber soled shoe and a bike tire were used to scuff a section of concrete and a section of the SR glass.
The rubber on the glass came off with the simple wipe of a finger: it didn’t stick well to the glass. That was not the case with the porous concrete: the skid marks were very hard to remove due to the porous nature of concrete.

We long suspected that the simple act of tires rolling over a skid mark on the glass would be enough to loosen the material, which will then blow off or be removed the next time it rains. This hypothesis was given credence by testing performed during our third USDOT contract. The Advance Loading test performed at Marquette University showed that the tires rolling over the glass panels did indeed keep the panels clean. See video here. Link to the proper page in Research.

One lingering exception may be spills from oil, transmission fluid, etc. A possible solution for those substances is a common natural compound called titanium dioxide (TiO2). Consultation with a manufacturer revealed that titanium dioxide turns substances like oil and grease into a powder, that would be blown off by wind or washed away by rain. It is currently used on building facades to keep them clean. One manufacturer reported to SR that roads sprayed with titanium dioxide only needs to have it reapplied every few years. We had a piece of glass treated with titanium dioxide for testing. We placed drops of motor oil on the surface and set it outside (the sun acts like the catalyst). The next day, the oil was gone and there was a powdery residue (most of the powder had blown off).

If needed, street sweepers may be employed where needed (vehicles with large rotating brushes). They are used in Idaho in the spring to clear the roads of the sand that was used for traction during the winter months.

Disasters

People ask how would a Solar Roadway® glass panel be likely to fair in the event of various disasters?

It’s to be expected that any force that could destroy an asphalt or concrete road (e.g., an earthquake, sinkhole, or landslide) would have a similar result with a Solar Roadway®. Power will not be lost however: only the damaged panels will stop producing, while any nearby panels that are intact would continue to produce power.

Another advantage of Solar Roadways® in regard to such disasters is their ability to double as an early warning system to alert residents of an impending hurricane, tornado, or the like. The road lines could flash in a particular color (to be determined by DOT officials) so that drivers would know to immediately check local weather reports and avoid danger zones.

Similarly, the roads could create detours and redirect residents away from areas of danger, into safe areas. Most lanes of a highway could be repurposed to take drivers to safety, with perhaps one lane continuing to the danger zone for EMS personnel. Solar Roadways® anticipates consultations with earthquake scientists to see if embedded sensors in some SR panels might aid in data collection and prediction.

Solar Road Panels could be airlifted into areas struck by disaster to be set up as a temporary medical triage and food distribution area, providing power, light and heating elements in winter.

Solution to the Infrastructure Crisis

ASCE (American Society of Civil Engineers) gives report cards to all forms of infrastructure: