Think about your average solar collector. Even if you have no idea how the dang things work, you know that:

• They are flat
• They are black
• They don’t work in the shade.

What else fits that description? With a few exceptions on the shade angle, the world has a lot of asphalt baking in the sun. A lot. Anyone who’s gone barefoot in the summer knows how hot a street can get. With that much surface area, you would only have to convert a tiny fraction of the solar flux into useable energy to make a huge difference.

So, come on, science (or maybe this is one for the engineers), give us a way to turn all those square miles of asphalt into cheap, low-efficiency solar collectors.

• In my head, it was more “mix something into the matrix of the asphalt that makes it a crappy photovoltaic cell. Attach wires. Have a beer.” This is far more complex, far more efficient from an energy-per-square-foot perspective, and brings with it its own barriers to adoption. But keeping the roads clean would be a new priority.

It would be very cool if these guys actually succeeded, but they have a long way to go.

And speaking of my crusade against false precision in calculations, on their numbers page they go from 112,610 million acres (5 decimal places of precision) to 43443.54 square miles (7 places). Then they add 2.5 million acres (2 places), and then multiply that by about 2/3 to get 31,250.86.

Won’t they be embarrassed if the surface area of streets and parking lots in the US is only 31,250.85.

All the rest of the calculations on the page are still impressive if the result of the above is “about 30,000 square miles.”

1. Hmm. The better a parking lot works, as a parking lot, the more shade gets cast on the solar collectors. I’m a bigger fan of building roofs over parking lots and putting the solar arrays on those. Yes, it involves more construction, but it also shelters parked cars. I’m more open to solar-array roadways, except…

IMO, there’s a more important function for many of our roads and parking lots. They need to be porous, to allow rainfall to soak into the ground and recharge groundwater, preventing erosion at the same time:

• Very cool. Enough porous roads and maybe once-a-century floods will go back to happening once a century.

I note that the working part of the road in this application is still good ol’ asphalt, and that the porous sections are in the bike lanes. Hopefully the water can move through the material quickly enough to not puddle up.

The material is also acting as a filter, to keep non-point-source pollution out of the ground water. I wonder if that means it has a finite lifespan.

There’s nothing to say that the porous road can’t also be photovoltaic. Let’s get the boys in the lab on this, pronto.

• Laurel Curve, an accident-prone bend on highway 17, is topped with “permeable asphalt” to prevent hydroplaning during winter storms. The change in texture is quite noticeable — at least if you drive a glorified go-cart. But the permeable asphalt is a three-inch layer on top of regular asphalt, which sheds the water to the sides of the road.

I’ve read that modern roadbeds count on the paving above for protection from water, which is probably why only the bike lanes are porous in the example above. But this just means we need better roadbeds. Permeable concrete exists, so let’s cap slabs of that with permeable asphalt and let the water percolate through.

All this porosity would probably be a problem in cold climates, where ice crystals would destroy things in short order. I guess that’s where those heated photovoltaic roads would come in handy.

Finally, in a presentation on permeable concrete I attended a few years ago it was admitted that such surfaces need to be vacuumed peridically, to keep the pores open. OTOH, some research done in Davis indicates that spilled vehicle fluids like oil and antifreeze get flushed down to the underlying soil, where bacteria digest them into more benign compounds.

2. This just in from the Netherlands:

World’s first solar road. Only it’s actually a bike path. The article was written in crayon by a five-year-old, but apparently the road can power things that use electricity.