Air pollution is one of the biggest environmental health dangers in the world. Transportation, primarily moving cars, contributes to air pollution significantly, producing 8 billion metric tonnes of CO2 annually, with 74% of this total attributed to them. To enable the electrification of light, medium, and heavy-duty transportation sectors and improve localized air quality while reducing pollution, there is a need for the production of clean energy.
Since many countries still heavily rely on burning fossil fuels to produce electricity, which transfers emissions from the tailpipe to the power plant, the proliferation of electric vehicles does not always translate into a decrease in global emissions and pollution. Although building equipment to harness renewable energy sources like solar and wind is undoubtedly beneficial, there are also drawbacks related to aesthetics and their influence on agricultural land. Nuclear energy, while also ‘renewable’, raises more serious issues with regard to public perception and safety.
One such recent breakthrough and application that is the topic of additional investigation for addressing the production of clean energy for the transportation industry is the installation of solar highways to support the electrification of light, medium, and heavy-duty fleets. Solar highways convert solar energy that strikes the surface of the road into electricity using Photovoltaic (PV) technology using existing road networks. This clean, renewable energy is then either used directly or sent to the grid to power road infrastructure.
Some of the benefits of solar roadways are:
1.) They provide renewable energy
2.) They help in maintaining good road conditions during winter, i.e., defrosting
3.) They can be applied to diverse applications
4.) Other technology features can be introduced into the road such as lighting

Are Solar Roadways Safe?

Although there are a number of interesting benefits, safety appears to be of great concern with solar roadways as they are more dangerous than traditional asphalt roads due to multiple factors.

Reduced friction:

Manufacturers produce solar roadways from glass panels. When it rains and these glass panels get wet, the coefficient of friction significantly decreases, which means that adhesion from vehicle tires is significantly reduced. This results in increased stopping distances compared to traditional asphalt roads. Believers suggest that ‘texturizing‘ the glass panels will enhance the adhesion properties of the road. However, altering the surface properties of the solar panels to improve friction characteristics will likely significantly decrease the efficiency of the solar panels.

Reflections from PV cells:

The UK and Ireland have raised concerns about the ‘glare’ from solar panels when installed near, on, or along roads. In addition to concerns from highway agencies regarding the ‘glare’ affecting drivers traveling along the road network, aviation authorities have also raised concerns that the reflections from solar roads close to airports could create safety concerns during landing.

Durability:

Designers do not intend for solar panels to withstand the constant barrage of heavy loading caused by vehicles traveling across them. Therefore, researchers need to investigate significant improvements in the durability of solar panels. When traditional asphalt roads ‘fail’, the road usually breaks into small pieces that cause little damage to vehicles. However, the failure of solar panels on the road will likely be more catastrophic, which could cause severe accidents. In addition, the frequency of repairs is likely higher than asphalt roads, resulting in increased costs to maintain the road compared to traditional asphalt.

Reliability:

External roadside lighting, in-surface lighting, and easy-to-read painted instructions supplement traditional asphalt roads and provide them with extremely reliable features. Many implemented solar roadways have installed LEDs within the road to provide instructions to drivers. However, an argument suggests that these systems will not be as reliable as current signalling systems, which could result in poor-quality information being provided to drivers that could increase the risk of accidents. Furthermore, a tight viewing angle of 10° to 60° limits the visibility of LEDs, making them difficult to read at extreme angles. For example, an LED vertically facing is easy to see from above but seeing that same LED from an angle commonly involved with driving will be difficult.

Road noise:

The solar road installed in France by Wattway produced noise levels in excess of the noise created by traditional asphalt roads. In this case, the noise produced by vehicles travelling over the solar roadway necessitated reducing the speed limit of the road to just 43mph; significantly slower than the rest of the road network. This type of road system practically makes it impossible to install a solar road on any fast-flowing road network because reducing the road speed limit will be necessary to mitigate the excessive noise it produces.

Do Solar Roadways Make Sense?

Due to the cost, usability, and efficiency of solar roadways, both urban and rural areas have difficulty implementing them. While these difficulties persist, the decreased energy production from the use of fossil fuels and enhanced air quality favor their climate-friendly credentials. This is especially important in cities where light, medium, and heavy-duty mobility can be electrified.
Solar roadway initiatives still receive financing from governments and other low-carbon project development institutes despite the drawbacks regarding safety covered in the previous section. Researchers have tested solar roadways in several locations and configurations, ranging from single-track lanes to multi-lane highways. However, in all instances, the power generated by these roads was not as expected and was often significantly lower than originally forecasted. Furthermore, researchers found significant durability issues, resulting in many of the implemented solar panels within the road networks ceasing to function after a short time.
In conclusion, while solar roadways offer several benefits, their future use will be restricted and favored only in specific circumstances. This is primarily because of the simplicity of implementing other eco-friendly technologies as opposed to the difficulties associated with solar roadways. Furthermore, producing renewable energy using solar panels will find more favour when installed on buildings and configured to operate with maximum efficiency.