Remember solar roads? Five years ago, the idea of building insanely expensive solar panels on the ground and driving pollution-spewing vehicles over them was all the rage. Scientists pointed out the obvious flaws. A flat surface that can’t tilt or move to capture sunlight doesn’t hit very high-efficiency targets. Driving pollution-spewing vehicles over the solar panels in question would inevitably hurt their ability to gather sunlight as pollution built up on the surface. Putting solar panels on the ground and then driving over them is an excellent way to smash said solar panels to flinders. In short, the grand push for solar roadways left a lot of very smart people wondering why we didn’t just put the same amount of money into building conventional solar panels and wiring them up in the normal fashion.
Naysayers, all of them. The campaigns to build various solar-powered roads took off. The Dutch, at least, saw reason in one regard and deployed them as part of a bike path rather than attempting to craft a workable system from running pollution-spewing vehicles over a surface that gathers energy from sunlight.
Now, some years after the first solar roads opened for business, they’re… well, an abysmal failure. According to French newspaper Le Monde, the roadway-building effort failed in part because the builders didn’t consider how robust the construction would actually need to be. The “Wattway,” as the French solar road installation is known, is disintegrating much more quickly than its builders anticipated.
This is a fairly common issue. One reason the US highway system requires so much more maintenance than its builders ever anticipated is that the weight of the vehicles we’ve allowed to travel on the highways has increased so much. Roadway damage rises as the fourth power of axle weight, which means an 18,000-pound truck does 3,000 times more damage to the pavement than a 2,000-pound car. French vehicle weights are going to be different and farm tractors aren’t going to weigh as much as a semi. But the point stands: These roads weren’t built to the required standard, even though the manufacturer, Colas, promised that the resin would withstand the weight of 18-wheeler trucks.
The problems, however, go deeper than just vehicle weight. Thunderstorms have damaged the road. Rotting leaves clogged it. Pale splinters of resin have broken off the surface and the end of the road is now truncated. It’s described as “pale with its ragged joints,” with solar panels “that peel off the road,” and splinters of enamel resin falling from the panels they were intended to protect. Total power production has fallen every year the road was in service. The roadway targeted 790kWh per day but managed just 409kWh/day in its first year of operation. It fell sharply thereafter due to damage, producing 215kWh/day in 2018 and has slipped down to ~200kWh/day in 2019.
The French government invested a relatively small amount of money in the project (5 million euros), but the efficiency problems with the design were fully apparent before ground was broken. “Our system is not mature for inter-urban traffic,” Etienne Gaudin, Colas’ chief executive of Wattway, told Le Monde.
The problem is not the system. The problem is the concept. There is no known manufacturing method that would allow for the construction of cost-effective solar roads that can both withstand the weight and strain of daily driving and deliver acceptably efficient power. Actions taken to improve the efficiency of a road for gathering energy — like tilting the roadbed to match the sun’s travel across the sky and cleaning oil, dirt, and grime from the panels — would make it a less-effective road. Creating a more effective road by using better protective coatings or cheaper manufacturing materials would make the road a less-effective solar panel. Given that solar roads are already far less effective at producing energy than conventional solar installations, one wonders why we don’t leave the roads for driving and optimize the power infrastructure for the specific job it’s good at.
There are lots of great flavors that go together. Chocolate and peanut butter. Salt and vinegar. Butter and popcorn. Ham and cheese. There are also a number of flavors that don’t go well together at all, like steak and tetrachlorodibenzodioxin. We submit that solar roads are much closer to the latter than the former. The idea might not be completely without merit if evaluated in very sunny areas where people primarily bike or walk, but it’s never going to match the efficiency of a conventional array. Outside of specialized applications, it’s time to turn the light off on this idea.