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Solar roadways: the next road revolution?

27.05.2019

Solar roadways are starting to pop up all over the world, promising to optimise the dense road network while offering undeniable advantages in terms of energy and the environment. But all is still far from perfect.

In January 2019, China opened the world’s first solar highway, the Jinan Expressway, about 400 kilometres from Beijing. A two-kilometre stretch of the road is paved with solar photovoltaic (PV) panels, which could produce up to one million kilowatt hours (kWh) of electricity per year. According to its designer, the roadway could provide enough energy to power 800 Chinese homes. The PV panels are embedded in the pavement and protected from vehicles by a layer of transparent concrete.

The objective of this innovation is to give roads a second function and source renewable energy. It is based on the same technology as traditional solar panels, only it gains space by capitalising on the existing road network and thus produces energy without destroying natural areas and farmland.

Recharging electric vehicles

Better still, the “sun highway” is self-sufficient because it can power its own traffic-light, video-surveillance and street-light systems, and even melt snow on the road. It has also been designed to anticipate future changes in mobility, because its paving will eventually make it possible to recharge electric vehicles using induction, just by driving along it. In the near future, the solar roadway could therefore help accelerate the development of electric car usage exponentially, drastically reducing CO2 emitted by road traffic.

A glow-in-the-dark bicycle path

Other experiments with solar roadways have been launched in Germany, France, Luxembourg, the United States, Japan and Monaco. In 2014, the Netherlands was the first country to develop a solar bicycle path. This invention was taken up two years later in Poland, in Lidzbark Warminski, where residents ride on the world’s only solar bicycle path to light up by itself at night. The path is clad in phosphorescent particles that absorb the sun’s rays during the day and release the energy in the form of light after dark. The material used can glow for ten hours, and the system runs and recharges itself continuously, without human intervention. The innovation also eliminates the need for street lights and provides an undeniable ecological step forward.

However, France is the real pioneer in solar roadways. The first kilometre of the technology was put down on a secondary road in Normandy in December 2016, on the outskirts of Tourouvre-au-Perche. According to the French Environment and Energy Management Agency (ADEME), the project was supposed to supply enough energy to power the outdoor lighting for a town of 5,000. Yet it produced only half the electricity hoped for, at a cost of €5 million per kilometre of solar roadway.

Doubts on solar roadway effectiveness

In addition to the extremely high cost, solar roadways have raised many questions concerning their real usefulness and effectiveness. This is because the denser the traffic, the more the road is in the shade and the less solar energy can be collected. Roads with both high exposure to the sun and low levels of traffic must therefore be chosen, which reduces the road network’s dual functionality considerably. Experiments have also shown that the amount of renewable energy produced by solar roadways is two to three times lower than that generated by a roof-mounted PV system, with a cost ten times higher. From a technical point of view, it is also better to install PV panels on an incline rather than flat to achieve the greatest efficiency. Lastly, many people have expressed reservations as to solar roadways’ resistance to frequent lorry traffic. And things such as dust, dead leaves and rubber deposits from tires can change the surface of the road and by extension the effectiveness of the procedure. For example, a solar roadway in Bellevigny, in the Vendée department in France, only lasted 18 months. This is not to mention the damage caused by storms, hail and other bad weather, which can seriously reduce output.

The solution to these issues may have been developed in Switzerland, in the form of a rather particular solar roadway. Starting in 2020, solar panels will simply be installed above 1.6 kilometres of the A9 highway. If this idea catches on, car travel will take place in a sort of tunnel. However, while solar roadways could still use a few adjustments, they might just be a very viable solution to the twin problem of the enormous demand for renewable energy and the need to repave thousands of kilometres of roads.

 

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