Most solar panels are very inefficient at converting the sun to electricity so they need all the help they can get. Two things solar panels require is to be clean and to be perpendicular to the sun. A solar road achieves neither of those things.
Median strips and easements are a possible siting location.
Shade awnings over car parks another.
The challenge with solar power really isn't sufficient area for siting. It's low-cost installation and low-disturbance environments which ensure long panel life and low maintenance costs.
Solar panels have a useful lifetime of about 20 years, due to numerous degredation mechansims (it's not just one), from fogging of the transparent surface to cracking, glazing from dust and sand, hail impacts, broken circuits, etc. NREL (the National Renewable Energy Laboratory) in Colorado have published research on this.
Engineering low-cost, long-lived, readily installable and replaceable panels would be a generally advisable research direction. Looking for extreme siting locations (e.g., high-traffic highways, or even sidewalks), or even, counterintuitively, greater efficiency, is relatively unimportant as compared to total costs and lifetime.
numerous degredation mechansims (it's not just one), from fogging of the transparent surface to cracking, glazing from dust and sand, hail impacts, broken circuits, etc.
Hasn't a lot of research been focused around ways to capture incident light and focus it down onto the actual cell surface? Iirc a lot of that has been things like surface coatings but is there really a requirement that's such a surface actually be in contact with the cell? Could there be something that was effectively a replaceable capture top surface possibly with an air gap above the actual photovoltaic cells?
A concentrating system isn't going to reduce the overall degradation -- yes, there's less critical surface, but it's weathered about the same as a nonconcentrating surface, and affects proportionately more generating capacity.
Or at least that's the theory.
NREL conduct longevity / degradation studies for numerous specific PV panel designs and products. Degredation ranges between about 0.5% and 0.8% per year, with an effective lifetime of 20-30 years.
Rough number, and actual results depend on specific siting characteristics and events. A tornado passing overhead, sandstorm, or very severe hail, may significantly negatively affect experienced lifetime.
I was actually thinking in terms of the pv and concentrating layers being physically separate, with a way to replace the concentrating layer similar to how roads are regularly resurfaced by removing an inch or two of surface and laying new asphalt.
The lifetime is better than 20 years. They produce 80% off their original power after 20 years but it's not like they stop working. Nobody would bother replacing them at that point.
Correct, in that the degredation is to about 80% of original rated life. Actually, checking on NREL's site, it looks as if there's been some improvement, with 25 years a more accurate estimate. https://www.nrel.gov/pv/lifetime.html
However the point remains that 20-25 years is the standard rated lifetime for planning and estimating purposes.
My 5 min of reading the article and thinking about it idea is thus:
A slanted roof angled to shade and water/snow protect the road, shedding runoff in to a gravel area beside the road with drainage considerations accounted for. The far side might have some sort of attached tarp over part of it, and there'd be a gap between top of said tarp and the bottom of the panel roof. That would promote heat-stack ventilation along the underside of the panels and thus also SOME cooling.
Those things are necessary to get the opimimum amount of electricity but the point of solar roads is to sacrifice some efficiency for the benefit of having huge amounts of surface area. The amount of paved highway in developed countries is enormous, so even massively inefficient solar roads could supply all the electricity necessary and more.
Go, fire up your favourite sattelite image service and check out how much of a typical urban area is really sunlit streets or parking lots. Bonus points for images where the cars that are present are on it. Ah and in an urban environment count shadows in. And quarter whatever figure you got because of dirt, abrasion and failure.
And now compare them to the areas of rooftops you find. Go ahead and do it.
If we're talking about highways, you can usually find large stretches of empty space immediately alongside them, at least the same width as the road itself.
Sure, and above the road, and on the tops of buildings, and all over the place. Solar roads are a bizarre idea. The only point I was making in my post is that if all roads generated electricity they wouldn't need to be very efficient, so using that argument against solar roads is flawed logic.
How so? How expensive is an inefficient solar road vs a regular road with a more efficient solar plant next to it? I imagine that doing them separately would at least make each last longer, and would probably be cheaper on average.
Let's assume a good solar panel yields 15 watts per square foot under direct sunlight. The DOT estimates about 1.5 million acres of interstate in the US.
Without getting too complicated, let's assume we produce at our ideal wattage for 3 hours a day. Given our ideal solar panel, this is 2.94 billion kWh per day.
Getting ideal conditions on a highway surface is unrealistic, so let's assume our fictional extremely rugged solar panel can only yield 0.25 watts per square foot. Now we're sitting at 49.01 million kWh per day.
To put this into perspective, the US produces roughly 11.45 billion kWh per day. So turning all of our interstates into inefficient solar panels covers less than a half a percent of our energy production.
Caveat: this is shitty napkin math and omits all other paved surfaces in the US of which I'm sure non-federal roads and parking lots make up a lot of, but I couldn't find good sources for those.
That puts your estimate out by a factor of maybe 25 or more (depending on road width) if all roads are converted to solar. And that's before the other paved areas like parking lots.
I'm not advocating solar roads. They're a strange idea with many, many flaws, but the inefficiency aspect isn't one of them. If you want to generate lots of electricity with solar you can have one very efficient array, or lots of inefficient arrays. Solar roads are the inefficient one.
Also, I would be preocupied by the ways to carry this hypothetically produced energy.
Right now we have either small "local" productions with "local " consumption (that works well as there is little distance to be covered) or "large" production concentrated on one site and with tension raised to thousands of volts to allow delivvery to the final user.
A "solar" road would probably make sense only in urban areas (where there would be other issues, like - say - shadow from buildings, less time of road free of vehicles, etc.) to avoid the issue of transporting the energy for long distances to the final users (or have a huge loss in the process).
Why the 60x output reduction in normal vs. road solar?
With say a probably still generous 6x derating, it would mean 2.94/6/11.45 = 4% of electricity production.
If you manage to avoid road solar tax (say by putting it above the road), it gets to about 25% of electricity production. Assuming a less pessimistic capacity factor of say 16% [1] gives 32% of electric production. Build a 3x wide solar cover over the interstates and .. use your imagination.
