Solar Roadblocks

There are many reasons to love George Takei. But this is not one of them:

Takei’s tweet helped the Solar Roadways project’s Indegogo fundraising campaign blow past its million-dollar goal. Their plan is to replace asphalt road surfaces with durable solar panels with embedded LEDs and sensors, turning highways into smart power-generating grids that can melt snow and give drivers safety warnings. Each individual hexagonal panel is capable of cranking out only a few watts, but if you do out the math on replacing all our highways with the the panels, it comes out to a ludicrous sum, well more than the United States’s entire current energy consumption.

It pains me, then, to say that the idea behind Solar Roadways isn’t just crazy; it’s obviously crazy. It’s Troy Hurtubise crazy; it’s Dr. Evil crazy. All the hype around solar panels and LEDs simply disguises the fact that Solar Roadways fundamentally misunderstands what a road is.

A road is a system for distributing moving loads into the ground.

That is its one indispensable job: to allow people and vehicles to travel atop it while absorbing the forces they create. I don’t claim to be a civil engineer. But I know enough high-school physics to be capable of asking questions whose answers are nowhere to be found on the Solar Roadways site, in any technical documentation, or anywhere at all on the Internet (so far as I can tell). Solar Roadways has simply not attempted to address the bread-and-butter engineering problems that highway builders have spent decades dealing with. Here are a few:

  • What do the solar panels rest on? The sublayer beneath them has to be made of something. That something will receive the forces transmitted downwards through the panels, and that something will degrade over time. To fix it, you’ll have to remove and restore the panels.
  • Cars and trucks will put their weight unevenly, on different parts of the panels. How resistant are the panels to bending? To shearing? These are different from the simpler question that Solar Roadways does discuss: how much weight they can take before being crushed.
  • Cars and trucks will accelerate and brake and push against the air; they have to push off against something. Solar Roadways has thought about traction. But receiving the force from vehicles is only half the problem, because they must also transmit the force to the sublayer. How are they anchored to it? How will the anchors deal with the immense lateral force of a braking tractor-trailer?
  • Water will get between and below the panels, especially in climates where the panels are supposed to melt snow. What happens when that water expands as it freezes? What happens when it freezes and unfreezes repeatedly?

I am not suggesting that these are insurmountable engineering challenges. We live in an age of near miracles. I am simply suggesting that they are challenges, and that they are obviously challenges. Not to see them fleshed out in the slightest is deeply discouraging, because it means that Solar Roadways is not approaching a gigantic engineering problem as an engineering problem. Even the Hyperloop—the Hyperloop!—came with a design document that tried (if not always successfully) to think through the engineering issues. When your futuristic transport technology is bigger vaporware than the Hyperloop, you have a problem.

It is not as though these are exotic problems, like building a quantum computer. These are familiar problems; they are the bread and butter of highway engineers. But no one has asked in detail, “What problems do road-builders currently solve, and how will solar roadways deal with these same issues?” Asphalt, for all its other issues, distributes moving loads quite well for its price point. To work as roads, Solar Roadways will need to replicate that success. Leave the solar panels and electronics aside for a moment: if building road surfaces out of thick glass was a good idea in its own right, we would be much more familiar with glass roads.

But assume even that these issues are all in the end solvable. Will they be solvable at cost? Almost certainly not. Solar power engineering faces its own significant design constraints. We are making progress in bringing the cost down, but still this is hard stuff. These are completely different design constraints than highway engineering faces. Why on earth would you insist on solving both sets of problems simultaneously in the same surface, if you didn’t have to?

There is no plausible future in which solar-panel roads make more sense than solar panels plus roads. There are plenty of other places to put solar panels, and plenty of other ways to make highways smarter. Solar sidewalks. Solar medianstrips. Maybe these are also terrible ideas. But they are unambiguously better ideas than solar roadways.

Science and engineering, done right, can be beautiful and amazing. But it doesn’t run in the other direction. Something can be as cool and as awesome as solar frickin roadways, and still not work as science. I understand the impulse that made people open their wallets to support this appeal to progressive technology as a solution to humanity’s self-inflicted woes. But science is the pursuit of truth, not truthiness, and solar roadways are scienciness, not science.