In the future, vehicles may travel down roads covered by overhead catenary wires and on highways paved with solar panels. Several experimental projects already exist in China, France and Southern California.

The first section of a solar-powered highway recently opened in Jinan, China. The city of 7 million people is one of the most polluted in the world.

The 3,540-foot-long stretch of road is paved with solar panels that are embedded underneath the surface. Up to 45,000 vehicles a day pass over the road.

According to the builder, Qilu Transportation Development Group Co., the solar panels are capable of generating enough electricity to power highway lights and 800 homes. Engineers also hope they will eventually be able to wirelessly power electric cars driving on the road. They claim the material can withstand all kinds of vehicle traffic, including heavy trucks.

The photovoltaic highway consists of three layers. The uppermost layer is comprised of “transparent concrete” that has a feel similar to asphalt. The middle layer contains the solar panels and the bottom layer consists of a strip of insulation.

While China’s goal is ambitious, it’s not the first solar road in the world. That honor belongs to a small village in Normandy, France, that installed a 0.6-mile solar street two years ago.

The test strip was built by Colas, a leading road construction company, and the French National Institute for Solar Energy. The Wattway system combines traditional road-building techniques with photovoltaic technology.

Wattway solar panels are directly applied to existing pavements and can safely bear vehicle traffic of all types. Up to 2,000 vehicles a day pass over the solar road in Normandy.

“Wattway panels are comprised of photovoltaic cells embedded in a multilayer substrate,” says Herve Le Bouc, chairman and CEO of Colas. “These 15-centimeter wide cells collect solar energy via a very thin film of polycrystalline silicon that enables the production of electricity.

“On the underside of the panels, there is a connection to a lateral module containing the electrical safety components,” explains Le Bouc. “The panels can be used on any road around the world, and are able to bear all types of vehicle traffic, including trucks.”

Solar road projects have also been discussed in other parts of the world, including Australia, India and Germany.

In the United States, a startup in Idaho called Solar Roadways has received federal government funding to test its technology. The company claims that its system not only creates electricity, but also warms up roads, making winter snowplowing unnecessary.

In Carson, CA, another type of electric road is already up and running. The 1-mile-long eHighway features electrified lanes that are supported by an overhead catenary system. It supplies electricity to modified semi-trailer trucks that are equipped with electric motors.

The system operates similar to the way streetcars work. Trucks draw power from the wires via pantographs mounted on the cabs.

The pantograph can connect and disconnect automatically with the contact line via a sensor system while the trucks are moving. This allows them to easily switch lanes or pass other vehicles without being permanently fixed to the overhead catenary system like a streetcar.

To further ensure the same flexibility as conventional trucks, the eHighway vehicles use an electric-hybrid drive system, which can be powered either by diesel, compressed natural gas, battery or other on-board energy source when driving outside of the catenary lines.

The natural-gas hybrid and battery-electric trucks were developed by TransPower, while the diesel hybrid was developed by Mack Trucks.

The eHighway technology was pioneered in Europe by Siemens, which is partnering with the South Coast Air Quality Management District on the Southern California demonstration project.

A 2-kilometer trial is also underway on a highway near Stockholm, Sweden. And, three field trials of the technology are planned for German highways in 2019.