In the United States, the primary mode of transport is cars — and when you have many people driving, you need a lot of road. In total, there are around four million miles of paved road in the United States. According to one estimate, that’s more than 13,000 square miles of paved land.
These roads have a big impact on their local environment before, during and after construction. First, there’s a carbon cost to laying asphalt. After construction, when it rains, the impervious surface of the road can carry polluted rainwater directly to storm drains — where the water will run off into the environment.
There’s also evidence that expanding roads encourages people to drive more often, increasing emissions over time.
Without a major shift in the U.S., these roads are likely to stick around well into the future. As a result, environmentalists and engineers want to find ways to take advantage of all that open space and offset some of the environmental cost of roads.
Solar roadways — roads outfitted with special solar panels — have arisen as one possible solution to reduce the environmental impact of roads. If you outfit all these roads with solar energy, you can use that paved land to generate energy. At first glance, it looks like a good idea — but would it work in practice?
Why People Are Interested in Solar Roadways
While solar roadway technology has been theoretically possible for a while, interest in the idea has grown significantly over the past decade. This new interest is likely due in part to the growing availability of new solar technology like home solar systems and batteries.
Changes in road materials may have also made the idea seem more practical. In recent years, rising asphalt prices have many cities turning to concrete for their roads. Concrete is somewhat tougher and more durable than asphalt, meaning concrete roads may be a better candidate for projects like solar roadways, where damage to the road could loosen or destroy embedded solar panels.
Growing knowledge about the environmental impact of travel by car may have also inspired recent interest in solar road projects. After all, if we can find a way to make roads eco-friendly, we won’t need to worry as much about their potential long-term effects on the climate and the environment.
The Challenges to Overcome
No one has attempted a large-scale solar roadway yet — but the first few experimental applications of the technology have not yielded encouraging results.
The Wattway solar road project, built in the Normandy region of France in 2016, lined a full kilometer (0.62 miles) of road with 2,800 photovoltaic solar panels. The project engineers designed panels coated with a special resin containing silicone. The company behind Wattway said the resin was strong enough to protect the panels from the weight of an eighteen-wheeler.
While sound in theory, the project was a disaster in practice. The resin was able to mostly protect the panels from traffic at first, but the sound created by cars passing over the panels was so loud that the village had to limit local speed limits to just over 40 miles per hour.
Three years after installation, there are solar panels peeling off the road and the protective resin is splintered and shattered in many places.
In terms of energy production, the project was also a bust. While solar panels are decent energy sources in well-lit regions of the world, Normandy only sees around 44 days of full sunlight every year. The region’s strong weather, in addition to potentially damaging the panels, further limited the power the panels could collect.
On one hand, the Wattway project may seem like a failure of planning. The choice of region, road and materials were all suboptimal. The combination of these mistakes could easily have been enough to sink the project.
However, the Wattway project also shows the serious challenges that engineers will overcome to make solar roadways and other “solar surfaces” workable. To start with, designers will need to use panel materials that are strong, resilient to traffic without generating too much noise and easy to maintain. Project planners will also have to select the right region for the roadway and find a road with the right angle towards the sun for maximum energy production.
What Will Future Solar Technology Look Like?
Growing demand for clean sources of energy will prompt engineers and designers to continue searching for new applications for solar panels. Solar roadways, however, seem likely to remain theoretical in the near future. The challenges of road-ready solar panels and the limited amount of suitable area will probably mean that solar engineers will look elsewhere before turning to projects like a solar panel highway.