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The first solar road has turned out to be a disappointing failure (sciencealert.com)
214 points by prostoalex 67 days ago | hide | past | web | favorite | 337 comments

I never managed to see the advantages of having a solar road compared to just having a normal road with solar panels next to it. Or above it. Or literally anywhere else. In fact I can't think of many areas that still get direct sunlight that would make for a worse place to put solar panels than on the road...

The advantage that people wanted to get is that in the end you also get a road.

Roads take up space, cost money to build and maintain. If you build it next to the road the road need twice the amount of space and still require the space, construction and material for the actually road. If you build it above the road you get all the issue of overhead roof on a road (trees that fall on it, wind, height limitation).

In addition to saving money by not actually building a normal road, the idea in most of solar roads projects is that it combines the work of putting internet and power cables into the ground.

That it currently do not work economically is the issue that the article showcase. Maybe it will never work and it always will be cheaper to simply build the road with current construction methods, put internet/power cables under it, buy large lands (farming land?) and construct regular solar parks.

Other concept of combining solar panels and building materials that is argued as more cost effective are roofs on houses. Same concept as solar road, ie that you get a roof and a solar panel in one without spending the work and material for both, but I have no idea if the economics is better than solar parks or if it is cheaper to just build normal roofs and go the route of getting land and building solar parks separately.

> That it currently do not work economically is the issue that the article showcase.

It's more than that. We simply don't live in a world where physics is in favor for doing this.

Many people have done more than back of the envelope calculations to show this simply was a non starter.

Those (people who took money to build ) push this idea are either ignorant at best and dishonest at worst.

I do wonder if the concept could work on a sidewalk, given that they aren't being perpetually driven over by 3,000+ pound vehicles.

Water drainage is still going to be a big problem, as is damage/scratching caused by shoes, bicycle kickstands, trolleys, anything else with wheels that is pushed/pulled, you name it. Plus the simple fact that most sidewalks (at least here in the city) are often in the shadows of buildings.

It only makes sense to start thinking about sidewalks once you've covered all the roofs, which are way better in every sense.

There's a solar bike path in Holland which did pretty well. Exceeded expected yield the first two years but then dropped back to slightly under.


It didn't do well, they just marketed the failure as a success, and they were at scamming a different municipality for a follow up 'experiment'.

Why can't they just work on something that makes sense?

The ground pressure from a truck is around 150 PSI. A woman wearing high heels can match, and even exceed that.

So the sidewalk would need to be just as strong as the road.

It's not that simple. Looking at the damaged roadway, I see lots of punctate damage. That puzzled me until I read your comment. I'm pretty sure that it's gravel under truck tires. So the same force-concentration dynamic as high heels.

Not only that, a common problem round here (UK) is that trucks park partially on the pavement. They routinely crack two-inch/50mm thick concrete paving slabs. I'd like to see a solar panel that can withstand that.

Surprised this is getting down voted, this is a common example in physics 101 describing the concept of point pressure. Architects have to consider the point pressure of heels when designing certain walkways.

Common physics example, but it disregards how women actually walk and stand in heels. They walk on their forefoot, rather than balancing their weight on the heel.


Shows less than 30 N/cm^2 (40 PSI) for women in heels - and higher heels result in lower heel pressure. Forefoot pressure is higher, despite the larger surface area.

Yeah, and a heel surface area of 32.3 +/- 4.4 cm^2. There are shoes with heel surface area of sub 1cm^2.

I don't think the study invalidates parents claim, if anything it more it less supports it.

Even so. It would be a flaw to not consider that at some point in time a women may put full force on the heel. Thus the example is valid.

Also I have seen high hees being abused by walking mostly on the heel.

The woman in heels doesn’t ever slam on her brakes and skid.

That applies sheer stress to the road, but it doesn't really impact the compressive force or pressure applied, right?

Sidewalks are still flat on the ground, which is not great in much of the world (like Normandy) where sunlight comes in at an angle. You would still get some generation, but would it be worth it compared to cells mounted elsewhere at a better angle, with less need for hardening, and less accumulation of dirt? Doing this on the sidewalks would add a lot of costs and complications.

Better to build it above the sidewalk where it can be angled more efficiently and provide people with some sun/rain shelter.

Maybe a motorway hard shoulder would be preferable to a live lane.

So the problem is that a normal road costs on the order of $3 million per mile, and a solar road costs... 10 times as much. And it doesn't last as long.

It just does not make sense.

It is plausible, but how much money is actually saved if you need to build panels that can stand wear and tear of vehicles above them? Surely the engineering is different and more costly than regular panels that don't need to be built to withstand cars rolling over, plus their maintenance, no?

Or just put them above the road then? :P

Put them above the road and tall trucks can't go through anymore. Plus, the support structures needed suddenly become obstacles for cars to hit when making emergency maneuvers or drivers lose control, and now you've got tons of glass shards, electrified wires and steel supports falling down onto the freeway.

Under the road is literally the only option, and it's a terrible option at that. Rooftops - or better yet, former farm fields- are always going to be cheaper and more efficient.

There's a standard maximum height for vehicles that is taken into account for freeway bridges, so your first argument is nonsense.

The rest still stands, of course. If you absolutely do want to put solar panels in the same place as cars, starting with parking lots is clearly a better idea. Fewer problems with high speed collisions, the electricity is generated closer to where it's needed, and people will be thankful for having parking in the shade. (Still more expensive than putting panels on a roof or field of course.)

"Nonsense" would only apply if practice were as good as theory; a very very brief Google search will net plenty of results for freeway overpasses and pedestrian bridges being hit. One example:


This isn't really a criticism of the core idea to just say "what if somebody built it stupidly low", traffic lights have been fine my entire life and maybe some highways will have to be skipped or doubled for NASA/ military purposes.

You get two in one but for double the price of both combined and then some. Not to mention the horrible quality and durability of the two things you get.

I have serious doubts these experiments will lead to commercially successful implementations, but I don’t think it is useless to do them.

Reason? Solar cells keep getting cheaper and cheaper. That makes the costs of scaffolding to hold the cells take a larger and larger share of installation costs. In the limit where cells are essentially free, putting cells everywhere there is some large horizontal area will make sense.

Now, of course, we may not get close enough to that limit for this to make sense, cells may be too fragile for mounting in a road, there may be plenty of more profitable places to put solar cells, etc, etc, but that isn’t guaranteed, and we can’t tell without experimenting.

Except we don't actually need that much solar power and ground based installation is really cheap.

Further road surfaces need to be transparent for solar to work, handle high loads, channel water off the surface, and provide lots of friction in a wide rang of weather conditions. It’s an extremely difficult problem, but solving it without massive reduction in panel costs is kind of pointless.

Define “need”. If five billion people want to live as Americans live now, and Americans will all have flying cars (1), go on holiday in space stations, etc, and we want to put back the carbon of a few cubic miles of oil in the ground each year to fight climate change, what we “need” will be quite different from what we think it is now.

If solar cells become essentially free, we _could_ get there.

Also ”ground based installation is really cheap.” doesn’t matter. Putting cells in roads _may_ become even cheaper, even though the cells themselves would produce a lot less power per square meter.

”it’s an extremely difficult problem, but solving it without massive reduction in panel costs is kind of pointless.”

I didn’t claim it was easy or that it was efficient now. I just pointed out that reduction in panel costs can lead to a situation where using them in suboptimal settings can be economically viable, if installation costs are lower for that suboptimal setup.

And massive reduction in panel price has been the norm for decades. https://en.wikipedia.org/wiki/Swanson%27s_law:

”Swanson's law is the observation that the price of solar photovoltaic modules tends to drop 20 percent for every doubling of cumulative shipped volume. At present rates, costs go down 75% about every 10 years.”

(1) of course, if Americans start having flying cars, road surfaces may become a thing of the past.

I was more thinking We as in people alive right now. In 100 years things could be different, but based on current trends it’s not going to be useful in our lifetimes.

So many things are wrong with using solar road surfaces that it’s hard to make them look viable even if the panels cost nothing. Because that means electricity is worth very little, and you still need to integrate them into the road surface which costs money.

> In the limit where cells are essentially free, putting cells everywhere there is some large horizontal area will make sense.

Going down that road leads to solar power satellites, not solar roadways.

Why not both? Neither works right now, it's probably prudent to try as many interesting things as possible.

> Why not both? Neither works right now, it's probably prudent to try as many interesting things as possible.

1. Solar roadways is a terrible idea that will never be a good idea. It is strictly worse than building a roof over the road and putting solar panels on that.

2. Roughly half the renewable energy on earth comes from decaying isotopes and half comes from sunlight. If humans want more than that, they'll basically need to get it from sunlight not hitting the earth i.e. solar power satellites. That is a road that we'll eventually go down, but not for quite some time.

I don't understand why we can't pursue all of those options at the same time. Especially solar road vs laser energy from space.

Solar roads has the distinct advantage over covering all the roads in that it's not an eye sore and fits more seamlessly in the scenario we figure out the engineering.

> I don't understand why we can't pursue all of those options at the same time. Especially solar road vs laser energy from space.

There's this idea in economics called opportunity cost. The simple version is that if we fund bad ideas that can't possibly be good, we lose out on the good ideas we could have funded but didn't.

This is the reason you don't heat your house by burning paper money. You'd rather have rent and groceries and heat instead of really economically inefficient heat.

So you're saying space laser energy is definitively better than solar roads? I think that's a little preemptive.

> Colas, the company that built the road, said in 2016 that the solar panels were covered with resin containing sheets of silicon to make them capable of withstanding all traffic.

I'm going to bet they said that after the check cleared.

Considering how public bidding work here, they said that before the check was written, with everything that was necessary for winning the bid.

This was not at all a failure. They built a 1km experimental road. They gained valuable information about real-world performance and technical challenges. It's not as though they built a 100km long six-lane highway with unproven technology. They built a tiny one-lane trial to test a promising idea.

It was overhyped by politicians, but what isn't? Maybe they even steamrolled over engineering red flags. That doesn't mean it wasn't a valuable experiment.

The trouble with this viewpoint is that there are an endless number of things we could be trying, and it's more or less a zero sum game.

The idea was terrible on paper, easily falsified by back of the napkin math. The same amount of money could have been spent on, eg, testing the commercial viability of smoothing out grid loads by making ice off peak for cooling.

It’s never a zero sum game - we can try many things at once, some will work well, some will work poorly, some won’t work at all

Trying things helps us move forward

And some aren't even worth trying in the first place. Like this idea.

edit: I'm all for trying crazy moonshots. Just not down right idiotic ones that are pushed by pseudo-science and clickbait activism [1].


Excuse my ignorance, isn't this a technical challenge, rather than the idea in itself was stupid?

Isn't that saying shooting sky full of satellite for communication is stupid until SpaceX made loading anything to space 10x less expensive?

I would say the idea isn't worth trying because it clearly wasn't ready, ( I mean if napkin maths already show it is off by a factor of 10 than it really is stupid trying it ) but I don't think the idea in itself is stupid at all.

The thing about solar roads is they're covered by cars, and they don't work when covered, for obvious reasons. Then all the road dirt, grime, tire dust, oil, etc, builds up on top of them blocking the light for good. The road is about the worst thing you can possibly try and generate solar electricity from.

Thx. Valid Point.

What is the point of a solar road?

It shouldn't be zero sum. We should try every feasible idea we can, and humanity has a blind spot for funding projects that aren't sexy and don't have the chance of outsized commercial returns, like cheap lenses for third world countries. Or insulation.

But that's the ideal. In the real world, political and consumer attention for projects like this most certainly is zero sum. They quickly get fatiguing and you already feel like you've done your bit.

In fact, it's probably even worse than zero sum in practice, because after being burned on junk like solar roads, you're far less likely to vouch or open your wallet for the next cool sounding tech that comes along.

I understood the parent post's view as a zero-sum game among different proposals. There is a set, limited budget, and myriad ideas to choose from and test. Funding one idea means not being able to fund another. Thus, zero-sum.

Therefore, we should fund most probable test ideas as should any scientific endeavor. The parent post claims that this particular idea was not probable to begin with (a poor idea on paper).

The question, when you see something seemingly very dumb, is always "what am I missing?"

It seems unlikely that well-funded scientists are _that_ stupid. It's more likely either that we're missing some reason why solar roads are more efficient at first glance, or that they have some ulterior political motive where wasting the money is intentional. Either way, laughing at them for missing things every internet commenter immediately thinks of seems like a mistake.

That said, in this case, my first thought is, "we definitely haven't run out of better places to put solar panels". The specifics don't matter much when the US has plenty of unused space to put solar farms (even just "next to the roads"). I'm pretty confused by how far the idea's gotten.

In a world where funding is largely about your ability to market your product, I don't see why it's that unlikely. It's not even that they're particularly stupid, just that the market isn't magically immune to things like the sunk cost fallacy.

If people are still paying you for an idea that you might be somewhat sceptical about, are you going to stop doing it anyway? Maybe you will, but I imagine there are plenty of people where the money will just confirm their biases towards their work.

There are different reasons to try things, this is worth trying because we have so many roads and using even a part of them for energy production would have an enormous impact.

Lets see the easily falsified napkin math then

EVblog has some great videos about how bad solar roadways are, starting in 2014, and a good recap video in 2017 https://www.youtube.com/watch?v=rpwx-8s1M38

And also an update this year just after the failure of the experiment was announced: https://www.youtube.com/watch?v=dM50P4K9UVk

If you can deduce something from your current knowledge, you don't need to do an experiment for that. Certainly people knew that putting fragile semiconductors under roads isn't the best idea, but they went on and spent time and money. I would call this a waste.

Some people deduced one thing, and others deduced the other thing. There was plenty of excitement about this idea on this very site when it was first proposed. Seeing something once is better than hearing it a hundred times.

only because reasonable opinion were downvoted to hell from the easily excitable crowd. I distinctly remember because I was amongst the downvoted, and dirt/rubber was one of the common concern, and it's weird to read in the article "engineers didn't think about the leaves" like, randos on internet could tell you that, what kind of cheap ass engineers were involved in the design and feasibility phase?

The two large-ish HN discussions I found with a quick search both have critical comments at the top: https://news.ycombinator.com/item?id=11041245 https://news.ycombinator.com/item?id=11001779

Every Hacker News post has critical comments at the top, if you took notice of those you would never attempt anything.

> There was plenty of excitement

The point is there shouldn't have been. Some people deduced and others hoped or willed themselves to ignorance.

What problem does this solve?

On the other hand it could also be a scam and the public money wasted could be used for far more interesting experiments. Experiments that at least make sense on a conceptual level or where we really just don’t know how things would pan out in a real world scenario.

Solar roads are not that kind of experiment. Even given an ideal execution solar roads would give you the combination of suboptimal roads with badly used solar panels.

Unless glas turns out to be a superior road surface (which I doubt) and unless solar panels perform better flat on the ground under a layer of dirt than raised above shadows and with a well adjusted angle (which helps the rain to clean the thing and increases efficiency) — unless all of that, putting solar panels on the side of the roads or roofa will be way more economical and ecological.

This is literally bad design: something that looks good or innovative on first glance, but is totally inpractical and maybe even destructive the longer you ponder about it.

It didn't appear to fail in interesting ways though. If it failed in all the obvious, predictable ways that's not a valuable experiment

it's like that kid who envisioned that we could clean the ocean of all the plastic by laying a long catching device. but they never bothered consulting people who actually build ships and other seagoing vessels. and they didn't bother consulting people who've actually worked on this problem. I believe the biggest issue is that the plastic tend to float under the surface of the water and this thing floated on top of the water. and then in the end this thing just bunched up after a day, so it never really caught any plastic.

this is the problem when you have rich people pick and choose which ideas gets implemented. rather than having people who are actually intelligent and have experience driving innovations you have a constant flow of bad ideas. inevitable something will work and these idiots will claim that their process actually works. no, it's more like they have the money to afford a lot of failures.

As far as I know solar roads where never a promising idea because they have obvious shortcomings that this trial just confirmed. There are a million better places to put solar panels than under car tires. Once we've exhausted those would could start thinking about solar roadways.

But it wasn't a valuable experiment. Absolutely nothing was learned from it. It's some combination of delusion and fraud. Here's a video from 2014 discussing it: https://www.youtube.com/watch?v=obS6TUVSZds

Exactly, failure or not is a good thing, moving on.

"The engineers also didn't take into account the effects of leaves, which caused damage and limited the amount of electricity the panels could produce. They also didn't think about the pressure and weight from tractors, two locals told Le Monde."

They were warned about this.

I find it hard to believe they were really unaware. They either overestimated the durability of their devices or were running a quasi scam.

The latter is quite likely.

I have come across quite a few “green” initiatives over the past several years which are extremely questionable in their technicals - and all are taking public money, mostly from European Development Funds in the EU, and from similar bodies elsewhere.

They are usually highly visible, buzzword bingo initiatives. You see these projects in the press - a group grinning in hard hats, a colourful initiative behind them. You go back a few years later and it’s tape and barriers and broken glass and danger signs.

Whether folks start with good intentions but then move on, or don’t have adequate plans for maintenance (which then makes one wonder why funding was granted in first place), or simply see an opportunity to extract wealth from a public body, I don’t know.

An anecdote: a service station near my home in north wales proudly announced that they had received a grant to put on a turf roof, solar and wind power. EU funding. Three years on, and they’ve just announced that they’ve received a grant to do exactly the same thing. Plumbing the Europa site shows that the previous grant was paid, and the project reported as completed - but they never did a thing. I’ve seen the same cycle being pulled elsewhere.

There is such a push for governments to be visibly green that they are spending money on highly visible nonsense. The current elected power gets the boost for snipping the ribbon and providing the funding. Their successor gets a beating over the wasteful failed project.

There are good green initiatives happening, but it’s usually where nobody is looking.

> An anecdote: a service station near my home in north wales proudly announced that they had received a grant to put on a turf roof, solar and wind power. EU funding. Three years on, and they’ve just announced that they’ve received a grant to do exactly the same thing. Plumbing the Europa site shows that the previous grant was paid, and the project reported as completed - but they never did a thing. I’ve seen the same cycle being pulled elsewhere.

This should be reported to media, police or both - this is fraud.

After my previous experiences reporting fraud to the police, I think it’s best I leave them to figure this out for themselves. I don’t particularly want to be arrested, or charged with fraud.

I haven't seen anything from it yet that would convince me that it's not a scam. The fact that there are people defending this after all this time baffles me.

political stunt wasting funds.. someone clueless decided or was lobbied to pick this thing.

This + quasi-scam. There's a lot of money to be made in the "going green" space and if lying about your product gets you the contract, only the government (citizens) lose and you laugh all the way to the bank. I wish more government contracts had forced warranty / refund clauses (whatever those are called).

You could put those clauses in but the legal entity would simply go bankrupt. You'd need something to go after the principals to make this stick.

Fraud might suffice.

I know nothing of the details here, so this is total speculation, but I can imagine value in going with a solution you know wont "succeed", if the data you get from the failure is valuable. Like, no need to spend money trying to fix the tractor problem if the leaf problem is too severe. If in practice the leaf problem only deteriorates things by 30%, that's different than 80%, etc.

Spending the money to solve problems on your first run is likely to not actually solve all of them.

Then again, this could be a bold exercise in fraud and/or incompetence.

That's a pretty expensive experiment, and they could have tested each independently (install a few meters of panels near a tree and near a farm). Instead, they installed 1km of road and the minister of energy hoped to drastically increase the amount of these roads within a fairly short time frame (5 years), which tells me they didn't consider it an experiment (just a conservative rollout).

This feels like fraud to me, and some lack of reasoning on the part of the government officials who accepted this project.

Yes, $5M isn't huge by government standards, but it's pretty big compared to simpler testing options available to a company who plans to fall back to powering CCTVs (hopefully not with parking lot panels...).

As a proof of concept trial it wasn't very expensive. Unrelated, but just for comparison it cost about a much as Uber lost every 2.5 hours in 2019Q2.

They built a Minimum Viable Product for a trial and found out that it wasn't actually viable and didn't provide the hoped for value. They probably also learned a lot with real world experience (that they wouldn't have been sure to have in a staged setup) and may come back with something different in the future.

Personally I'd be curious about the math on how much these panels pick up, whether some kind of contactless power transmission would be viable at highway speeds, and whether in 15-20 years we'll see interstates paved with these providing trickle power to fully automated electric trucks running as "road trains" across the country.

Have there been any trials on creating a solar roof over highways? It seems like a much better option as the panels don't need to be reinforced, and they can be angled towards the sun to aid cleaning. We already know how to build stable metal framed structures (and panels aren't that heavy). In somewhere like Spain it would reduce the requirement for AC while driving, making it even more green. During rain it would increase visibility and reduce water on the road, making the road safer.

If you're building new structures I'm positive that the economics work out better for simply doing separate solar farms. Building them above a road has no major advantages and potentially both increases construction costs and increases the chances of unfortunate interaction (eg an accident taking out panels).

The sweet spot for solar roads would be in places where the generation benefit outweighed the extra cost when a road was being redone anyway - and even then only if the materials were up to the task.

I'll give you 1000:1 odds that we won't.

Sourced from road solar? Probably not.

Still, power sourced from solar or wind in general and adequate to offset some of the "maintain speed" level of power draw? That seems more likely. If you have some way to provide maintenance levels of power during movement that may mean a significant savings in battery weight and overall cost, and if you don't think that matters take a look at the skirts under a lot of trucks designed to reduce drag.

It's possible they did that, but in this case I think it's probably not a good idea.

When you want to launch a new technology it's better to have it do better than expected than to have it run into 'unexpected' problems.

my vote is for scam, or scam through culpable negligence. bet they loved all the attention though.

They either overestimated the durability of their devices or were running a quasi scam.

I'm leaning toward scam, because if it can't handle leaves, it can't handle anything.

Still, it might be a simple division of labor thing: one group specializes in believing, hard, and pulling in the money, another group says "well, they've got the money, let's try to build the least bad version of this travesty, if we don't take it someone else will"

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.

They also need to keep cool, another thing being under many running cars is not ideal for.

Panels at the side of the roads?

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.



But then, why put them at the side of the road as opposed to, well, anywhere really?

Exactly. We have plenty of room for solar panels.

panels above urban tunnels, maybe powering some air filtering system ?

You're on the correct track here.

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.

Aqueducts have been suggested as siting locations.


- Reduced evaporation losses.

- Extant rights of way / property rights.

- Extant technical infrastruction, including power transmission for pumps, etc.

Not that this is the only siting location to consider, but it's a reasonable candidate.

Never thougt of them. Great indeed.

Right? There are so many other good places with less issues, why pick the road-bed?

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.

> huge amounts of surface area?

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.

Could you talk more concretely? What is the back of the napkin calculation for total power if some percent of all highways were solar?

Not OP, but I was curious:

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.

There are 77,000km of interstate in the USA. (https://en.wikipedia.org/wiki/Interstate_Highway_System)

There are 4,000,000km of paved roads. (https://www.roadtraffic-technology.com/features/featurethe-w...)

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.

[1] http://euanmearns.com/solar-pv-capacity-factors-in-the-us-th...

Ok thanks, so now I'm trying to understand why the people behind Wattway couldn't make this simple estimate.

They didn't want to.

Be very wary of motivated reasoning.

Help me understand the logic behind taking a PV and stepping on it in the worst possible way, leaving dirt , rubber etc, when every PV that is exposed only to the open air needs regular cleaning / maintainance. And its being frequently under the shade of cars

There is no logic behind it, only blind idealism. Unfortunately the couple who invented solar roads poured a lot of time and money into this idea and couldn't back down. Many people followed their enthusiasm. I think one of the most difficult things you can do as a person is to be honest with yourself and admit when something has failed or won't work and to abandon it, but stories like this are reminders to really self reflect.

I'm curious how you arrived at that conclusion? Common wisdom, at least a few years ago, was "cleaning isn't worth it".


Self-cleaning glass is a fairly mature technology and will work effectively on a rooftop solar installation. That won't work on a solar roadway, which a) needs a textured surface to provide adequate grip for vehicles and b) can't retain any sort of coating due to friction and c) is constantly being covered in axle grease, tire rubber, brake dust and the innards of various wild animals.


This is for rooftop panels though. Having regular activity on top of something is, I would assume, very different than just letting it sit.

The article starts with the wrong assumption that you have to hire people to clean the solar panels. Robots have taken over that job a long time ago, at least for utility scale solar.

For some reason, solar roads are a very aggressive meme (in the classical sense of the word). They capture the imagination and blind people to engineering reality.

Solar roads do not make any sense whatsoever, as you wrote pretty much any other place is better for panels.

They capture the imagination because there are plenty of places you don’t want to build solar panels. Namely places that you want to leave alone for ecological or recreational purposes. If you can take a piece of infrastructure that is pervasive throughout a built environment and give it additional purpose, then you can save on or reduce the land you specify for this purpose.

Does it work? Apparently not, or at least: not yet. We have not successfully accomplished this, but it remains to be seen if this is a case of not yet, or never will. Experimentation yields useful data, even when the experiment is a failure.

So where were the failures? The road was less durable than expected. They didn’t account for falling leaves. They didn’t produce as much electricity as they thought it would. Thunderstorms also damaged the road.

But! It did produce a decent amount of electricity, it did successfully transmit it, and it did function as a road. Colas has given up and chose not to pursue this route anymore, but it isn’t a death sentence for the idea in its entirety. It is a failure of execution, and there will be a lot of failures before there is ever a success. I’ll end this with the caveat that there might not ever be a success, but it is too early to decide that and further experimentation might yield other interesting road construction technologies.

The thing is though that currently most roads are made from asphalt, yet even that is not durable enough and needs to be periodically reapplied, how a glass can compete with that?

And anyone who lives anywhere it snows knows how badly the roads get beaten up by snow plows and salt.

Snow plows and salt aren't even the worst of it. Every road is going to have some water in it and when the temperature drops below zero, that water freezes. Water expands when it freezes and this puts stress on the asphalt. You go through enough of these cycles and your road starts to breaking down.

It's not an experiment that can yield anything or teach us anything if there is no paper and no data. A fraudulent startup maybe.

How big is your laboratory? Is it a space you rent out, or is it all the known Universe and all of its history?

We’ve been learning things by trial and error a lot longer than we’ve been practicing the Scientific Method. You don’t always get the data you want. You don’t always get someone to summarize the data in a nicely formatted paper published in a respected journal. You get what you get and if not quite like it, make do.

If this sort of thing, Solar Roads, doesn’t interest you, that is fine too. Maybe you even have credible reasons to be Anti-Solar Roads. It’s certainly shaky enough ground to start on, but I wouldn’t discredit this road in France as a useful experiment simply because there wasn’t a paper at the end. Thunderstorms and fallen leaves! Maybe they should have known, but they didn’t, and because they didn’t consider that, it’s exciting because now how can we go about addressing the problem if we wish to try this again? Maybe someone can build a road and let it get hit by Thunderstorms just to analyze the rate of fire, so to speak. Maybe someone can build one somewhere else to figure out how it differs from one location to another. Maybe we build a third, and start figuring if a solar road is more likely to attract strikes from a storm than other types of roads? Can we mitigate this with some kind of lightning rod? How many do we need and how spaced apart should they be? Can we capture the energy from the lightning or are they too infrequent even in the vicinity of the solar roads to be worth the bother?

A lot of those questions might already be answered or answerable without having to build all of those roads to figure it out, but at the very least, a little roadway in France can spark a lot of questions that are worth answering for anyone trying this anywhere else.

It’s simply a waste of money if we can do the maths and see that it’s always going to be vastly worse than putting them on roofs, on gantries over roads, or literally almost anywhere else but on a dirty, flat surface with huge pressures on what we already knew were fragile and durable cells.

There are several factors, each alone that make this idea a non-starter. All these were known from previous experimental results so this never needed to be done. For example - 1. Placing cells flat reduces the power output by 30% over putting it at an angle and facing north. The angle varies with how far you are from the equator. So putting solar in roads will always yield at least 30% less power than putting it in an appropriate location. 2. Roads are extremely dirty. There’s dirt, brake dust, rubber, etc., not to mention shading from buildings, the natural geography and cars while they are driving over it. This will mean at least another 10-20% less power per solar cell, which will degrade as it gets dirtier. So you’re probably throwing up to 40% of your power away unless you’re cleaning them every week or so.

Then factor in damage, etc... a basic engineering assessment shows that it is infeasable, and even with massive improvements, rooftop solar and solar farms will always be correspondingly better.

But since you seem to be so big on experimentation, do you want to send me a few million dollars and we’ll put solar on the biggest area of all - the sea floor? Think of how much space there is! I mean, we can calculate that basically no light reaches it, but that’s not important, right? It’ll be valuable data!

(Note that when I say panels need to face north, that’s because I am in the southern hemisphere. Obviously in the northern hemisphere it’s the opposite so should face south).

Not how it works. It's not enough to try something, you have to share the knowledge with the community, otherwise there will be no progress until someone else willing to share the knowledge tries the same thing again. So, it's as good as didn't happen if there is no paper and no data (doesn't have to be a peer reviewed paper or anything like that).

There's abundant data. some 2 years worth of daily power generation from road installed PV panels. A ~$5mm experiment, that also resulted in a 1km road.

Your local physics department spends x10 that budget yearly, and you can't move your car on the arxiv papers it produces (if any).

P.S - Colas is not a startup https://www.colas.com/

> There's abundant data. some 2 years worth of daily power generation from road installed PC panels

I'm not sure how is this relevant. How this data can help engineer proper solar roadways? Where is the data on all the problems they had to solve and problems they couldn't solve?

What is the advantage of putting the solar panels under the cars rather than above them?

People drive into things over roads:


Imagine that, but with solar over the road- you now have sheets of glass shards, live electric wiring and support steel falling down over the road. Additionally, the supports (along side the road to hold it up over the top) become targets for collision as well.

The sheer amount of materials required to make it sturdy enough to survive tornados, general high speed winds, and the occasional accident from a moving vehicle means that you're going to have a hard time coming out carbon neutral- or at the very least, you'll lose a lot of the benefits.

Of course, putting the panels under the cars is a pretty awful idea as well. Simply put, they don't belong near roads at all.

Same reason Toyota decided to go with the scam and showed off PV covered Prius https://www.theverge.com/2019/7/5/20683111/toyota-prius-plug... Anybody with the smallest grain of engineering background will immediately spot the deception, but typical off the street person will think its brilliant!

How so? I mean, it's an image of cars driving over something which is kind of delicate.

Perhaps you mean roads with solar panels near them that feed the passing cars energy? Now that at least sounds exciting! (Although it's probably not a great idea either, not enough battery weight saving to be worth it.)

This was obviously never going to work; I think it's far more interesting as a piece of morality theater and/or a psychological ink-blot test. Because who looks at a system like this (individual humans carted around extravagantly in an energy-intensive, 4,000-pound CO2-belching murder machine, on an expensive and space-intensive road created just for them) and thinks, you know what's wrong with this system? It doesn't generate enough energy. Mmm yeah, you're almost right. Sort of like how a violent person doesn't generate enough not-punching-people. Keep going with that reasoning. See if you can use the phrase "in the first place" in your answer.

It's fascinating. Obviously they seem to grasp the system has something wrong with it, and the problem has something to do with energy. But when that line of thought begins to lead them inexorably toward the conclusion that they should actually probably stop driving immediately, like today, they take a quick left turn into something else, anything else, whatever's available and "green" - SOLAR, let's do the solar. That'll absolve our sins. Hence, where do you place the panels? In the road, where the sin occurred.

It's like the dim awareness of our actual transportation/energy predicament, is in the cellar of their subconscious, knocking at the door to enter conscious awareness, but not quite managing to get the person's attention. The mental contortions required to actually like this idea, remind me a lot of the ones required to maintain various states of denial. The fact being desperately avoided of course is that a set of changes far more sweeping and less pleasant than they're willing to admit or allow, are going to be necessary.

This was obviously never going to work

Could be, and I suspect that a lot of the actual engineering folks involved would agree 100% on this point. They'd probably also tell you that 5 million for real - world experimental data on the exact ways in which it failed was very much worth it.

Was there anything else worth responding to in the wordy pseudo-psychological insults?

May I please read the real-world experimental data that will save other companies millions of dollars?

Go right ahead.

Scientific papers are probably easier to access than anytime before.

Start by looking for optimal angels for mounting solar panels. Last I heard, unless you have movable panels the only correct angle is where they catch most of the sun in the middle of the day.

1.) I think the OP was asking where they can find the insights obtained from this failed solar road test that would allow others to save money. Not general photovoltaics stuff.

2.) Angling solar panels is a more complex problem than you might have thought: https://www.eupvsec-proceedings.com/proceedings?fulltext=mun... :)

That may not be made available depending on the company involved with the roadway. They may very well consider it proprietary information to be used in development of future products.

I remember at the time this was announced, I was working at a startup in the solar PV industry. Our collective response on the workfloor was, "wow, that's an incredibly stupid idea for so many reasons". Surprised it took them so long to admit failure.

If they had admitted failure earlier, then they couldn't milk as much money from suckers.

What failure? They got paid handsomely.

Seems like you'd be much better off floating them on a lake. There was a project a few years ago to do this both for power and to reduce evaporative loss in reservoirs, but I don't know if anything has come of it.

Such solar farms are built fairly regularly. Examples: https://www.bbc.com/news/uk-england-london-35705345, https://www.smithsonianmag.com/smart-news/china-launches-lar....

Putting solar cells on top of (artificial) lakes not only decreases evaporation, but also cools the solar cells, making them more efficient.

Floating solar is doing well, with global capacity over 1GW (global installed PV capacity surpassed 500GW).

It's technically easier to put things on land if possible.

Wouldn't you kill the lake, unless you only covered a small proportion of it.

Depends on the lake. There is a reservoir near LA covered in millions of black balls. Apparently this is a side effect of water quality regulation, direct sunlight triggers a chemical reaction that produces harmful byproducts. As a bonus, evaporation is also reduced, which matters in semi-arid climates like Southern California.


I saw that story surface again recently, it's a perennial pleaser. Those balls are used to cover lakes of processed water which is eventually used as drinking water; that's not a living lake.

This NatGeo article from 2015, https://www.nationalgeographic.com/news/2015/08/150812-shade... , notes for example that they kill algae and microorganisms, and inhibit water-fowl.

I'm almost certain they'd kill lake-born fish too, preventing growth of water-borne oxygenators (which also serve as a food source, and place for eg snails to live).

Whilst the purpose appears to be to prevent plant and animal life, at least in part, it's possible a stable eco-system might still survive; but it seems highly unlikely to me -- do you have something to show me I'm wrong in my assumption?

While I'm not an expert, I suspect you're right. Point being that some lakes serve a different purpose than supporting a thriving ecosystem.

If direct sunlight triggers a harmful reaction in your water, you need to reconsider what's in your water.

Not really. Bromide and chlorine are okay for humans to consume. Sunlight turns these into to bromate which is a carcinogen.


Okay, but do bromide and chlorine naturally occur in the water in that area? Or was it because of human meddling?

Cholera, dysentery, and many other waterborne diseases exist naturally in untreated water that hasn't been "meddled with" by humans.

The death tolls of historical urban outbreaks shows that you would MUCH rather drink the treated water.

Maybe you should just read the article I linked. If you have more questions, then you can google those and figure it out.

If through your process of learning, you come up with an understanding of any situation, then you should form an opinion.

I don't mean to be rude but your question is easily answerable by reading the article I linked (and it's a short one). If you're not going to take the 30 seconds to respect my comment, I will show none to your uninformed opinion.

They are part of the water treatment process for municipal drinking water supplies.

Though I'm not familiar with the specifics and details of this case (and have seen the Veritasium video describing the use), it's reasonable to assume that these treatments would be applied regardless, and the shade balls are an effective countermeasure.

I'm not clear why it matters. Everything natural isn't necessarily good.

Salts are everywhere, there's nothing wrong with trace amounts in water.

It's used in the water cleaning process to make it drinkable.

Lots of reservoirs or mining pits basically aren't suitable for life, and there are even more bodies of water that have areas that aren't. Sometimes that's because of pH or salt concentrations, but more often it's because they dry out seasonally, they're very low oxygen, etc. Many of those areas are large enough to get substantial power out of, and in the case of the seasonally dry reservoirs you might even be building a better ecosystem by reducing evaporative loss.


I am unable to downvote but I would if I could. Many reservoirs are for municipal water supplies and not for marine life. It is common to cover them to reduce evaporation. To jump to the conclusion that floating solar arrays would "fuck the fishes" is obviously not well thought out.

In the United States, very few reservoirs are exclusively for water supplies. Most large-scale reservoirs I've been to (probably 50 or 60 from Lake Mead[1] to Woodcliff Lake[2]) are also used for recreational boating, fishing, and wildlife habitat.

[1] https://en.wikipedia.org/wiki/Lake_Mead

[2] https://en.wikipedia.org/wiki/Woodcliff_Lake_Reservoir

A reservoir is not a "lake", by definition.

Wikipedia[1], and probably most dictionaries, disagrees:

> A reservoir (from French réservoir – a "tank") is, most commonly, an enlarged natural or artificial lake, pond or impoundment created using a dam or lock to store water.

I've been to plenty of reservoirs with "lake" in the name, and I didn't realize the closest lake to my childhood home was a reservoir until I was a teenager, and the name didn't have reservoir in the name.

[1] https://en.m.wikipedia.org/wiki/Reservoir

A reservoir is not a "lake", by definition.

Tell that to the Colorado River and its reservoirs Lake Mead, Lake Havasu, Lake Granby, and Lake Powell.

Solar roads seem like a really cool technology. Like, if they worked great and were affordable and everything, then awesome!

But, practically speaking, they seem to violate the [single responsibility principle](https://en.wikipedia.org/wiki/Single_responsibility_principl...). By coupling a solar panel to a road, we're forcing the physical entity to comply with competing objectives.

Seems like the future's prone to be different, anyway. For example, how long are we going to really need roads that're driven over at-random like today? Seems like self-driving cars could be designed-and-programmed to drive over just specific parts of the road meant to handle their weight, while the gaps between those load-bearing parts can have solar panels.

You know you kind of described how trains work? :)

I just did a quick calculation for Poland - we have 11k km electrified train tracks, with ~1.5m of space between the rails. If I calculated correctly, putting solar panels there would give us ~8-15tWh energy per year, which is 5-10% of the required electricity production for the nation.

I've never been a fan of the idea of solar roads, but solar railways might actually make sense...

Mechanical equipment, and freight, tends to fall onto tracks. Axels need lubrication, there are hydraulic fluids, potentially septic drops, and bulk containers (coal, sand, gravel, metal, scrap, grain) also leak from bins. None of these do much to improve efficiency or lifetime of solar panels.

Rail has adjacent easements. These have traditionally been used for complementary technologies, e.g., telegraph and other comms routes (which share a need for continuous rights of way, and provide a utility to the railroads themselves for communications and control services).

There are reasons you might want to avoid certain co-sitings (e.g., unarmoured petroleum or natural gas lines adjacent to rail trackage). But solar could well be a reasonable adjunct.

I don't know how they do it in Poland, but in some countries when you flush a toilet on a passenger train going above a certain speed, the nasty stuff just evacuates to the space between the tracks.

Seems like any sort of solar panel on the ground is going to be prone to get nasty stuff on it.

I guess they might just have them at an angle, then trust the rain provide some light cleaning, while a street/rail-cleaner could go by for more thorough cleanings periodically?

I mean, I dunno what exactly their strategy is, but I'm assuming that they're not counting on a road to not get dirty. Cars leave rubber from their tires, drip oil, drop trash, etc..

> Seems like self-driving cars could be designed-and-programmed to drive over just specific parts of the road meant to handle their weight, while the gaps between those load-bearing parts can have solar panels.

if you can drive that precisely, why even put anything in the gaps?

Same reason we have safety rails around roads. Plus, if we want solar roads, solar power would be a perk.

I mean, once the road is dominated by self-driving cars, presumably we can implement new driving requirements beyond what human drivers could implement.

For roads, we might want cars to drive over load-bearing parts, if that's optimal. Or if it's more efficient to have the wear-and-tear distributed, then cars can drive in staggered formations, much like a wear-leveling strategy in solid-state drives (SSD's).

But, there's no reason to design a transportation system around the premise that self-driving cars can't control their patterns just because human-driven cars couldn't.

Which isn't to say that we should assume that self-driving cars will be perfect or infallible, just that we can assume best-effort strategies. For example, we shouldn't assume that self-driving cars would never drive over a gap with a solar panel, but we can design a system in which self-driving cars try to avoid driving over the solar panels.

Solar Freaking Roadways! Do you guys remember this viral youtube viral video? https://www.youtube.com/watch?v=qlTA3rnpgzU

When I first saw that video I thought, “this has to be a joke right? They can’t actually think that is feasible.” And here we are…

The video attracted so much undeserved attention that many engineers felt that they had to produce a corresponding debunk video explaining why it is such a useless idea and why asphalt is currently our best option on building roads.

You know, I always wondered why they didn't go for solar covered sidewalks, which would provide shade to pedestrians and power to everything that needs it. Roads seem like a better place for pressure-based generation (of anything, frankly).

Still, just for the enthusiasm they garnered and the continued push toward making renewable energy generation interact with the everyday, the idealists should be commended. The engineers... not as such, no.

But, silly question, knowing very little about this field, couldn't it be possible to (co)generate power from the heat and pressure that roads endure on a near-constant basis?

Solar roads and sidewalks are a PR stunt. Abrasion is no joke, nothing optically transparent survives on the ground. You can see this easily in the cellar "pavement lights" common in NYC and other old cities. Light still passes through after a century, but maybe 20% and very diffuse. Bad for solar panels.

Roads don't absorb enough energy to generate power, they're not flexible enough. They're designed to not absorb energy since it hastens breakdown. Potholes are a good example of a road surface energy absorber :) .

Solar roofs are a far better bet. Elon is onto something there, but time will tell if costs can be brought down enough. Besides the good PR, solar roofs substantially reduce heat absorbtion, important in the sunny climates solar works well in. And we have a ton of wasted roof space. Many companies would willingly allow roof panels to be put up for free if the economics for power generation were good enough.

I actually love seeing the "pavement lights" in NYC when I walk past them, or recognize that I'm walking under them. At this point, I know they're purely decorative, but it was a nice touch and something idealistic that left behind something cool. As far as what I was thinking on sidewalks, the other response got it right; I was thinking of putting archways and solar roofing over sidewalks. It doesn't need to be high-yield, but the benefits really sound like they outweigh the risks (as a pedestrian) - keeps the sidewalk in shade, keeps the rain and snow off, and generally would make walking a nicer experience. I've been on covered sidewalks before (including the ubiquitous scaffolds in Manhattan, Hoboken, and Jersey City - I used to aim to walk by the buildings I knew had scaffolds up when the weather was bad out), and it's a better experience than just being outside. Plus, if it's covered well, I think it'd reduce the opportunity for pedestrian vehicle accidents; just from having less possibility of people and cars interacting.

EDIT: Also, thank you for answering about the road idea, it was a thought. Too bad it doesn't work. :-P

I think you misunderstood the parent, they said "solar covered sidewalks" that shade pedestrians, so roofs.

Solar roofs on car parks seem good to me; better than using pasture land converted to solar farms which I'm seeing more and more in UK.

Somewhat. OP also mentions generating energy from the pavement, which I don't think will ever be reasonable.

Solar car park covers are a great idea. Easier access than roofs, don't need to be water proof. Good cooling airflow underneath. Tend to be close to cities where power is easier to transport.

Solar parking lot covers are the best ROI solar installations I can imagine.

Surprised Telsa isn't doing this with their SuperCharger stations

Yeah solar roofs on car parks is pretty good because the shade aspect is just a bonus.

They did, I know of two sidewalks, both caught fire :) and never generated any power, one even needed external supply from the grid.

> pressure-based generation

That would simply inefficiently make the vehicles less efficient.

Who would've guessed? Getting a kilometer of solar panels installed as a road (sic!) in a region that has a cloudy skies most of the time. It's borderline genius. How did it get any approval at all? Who treated solar panels being used as a road (probably to spend some more tax money on casing?) as a good idea? How is it not just obvious that it will not even get close to the easier and cheaper (rooftop panels) options? This imitation of environment care is so hilarious that I don't have the proper words to describe it.

This was a PR stunt from the beginning.

We can't even make roads last 20 years with the most durable materials we can find. We make them out of rock and they still fall apart.

Car windshields are scratched to hell after a decade. Grocery checkout scanner windows are made of Sapphire, nearly as hard as diamond, and still need to be replaced.

Solar roads will never be a reality. Optically clear material hard and malleable enough seem a physical impossibly. Metals are the only suitable material and they cannot be made transparent due to hard physical constraints.

There is one and only one bright spot I can see in this test: the concept was trialed under ideal conditions according to its proponents, and failed spectacularly.

There's a high probability that true beleivers still won't be convinced -- their faith transcends reason and experience. The rest of us can point to this as a Provably Bad Idea.

My only regret is that there aren't similarly conclusive demonstrations possible in all such cases.

Interesting, though I think there's more to it than just this.

Belief tends to become identity.

Moreover, belief becomes an ordering principle. The refutation of a belief creates the problem that there is no longer an ordering principle. This isn't always clearly obvious, but if the belief is itself part of a complex chain of interconnected beliefs, then removal of one, even if quite clearly false, creates discord within the entire structure. You've got to break down and rebuild the whole thing, which can get complicated.

(Compare, by way of technical analogue, the task of refactoring a particularly messy bit of code or kit, where it turns out that a specific feature has interactions across a wide number of other areas.)

The Kubler-Ross model of grief is, I'm increasingly convinced, actually a response to belief changes. The original research was based on patients informed of their own pending mortality, by way of fatal diagnoses or conditions, and how they responded.

Such information is a massive disruption to belief systems. And absent some mechanism for supporting transition to a different one, the classic KR response (denial, anger, depression, bargaining, acceptance) is highly probable.

The interesting question to me is what happens in cases where such responses don't develop. Where we can and do change beliefs quickly and fluidly. What do those circumstances have in common.

If you can cope with the swearing, this is an interesting debunking of an other (US) solar road project with preposterous claims: [1]

[1] https://unreasonablydangerousonionrings.com/2016/07/18/4-rea...

As a side note, falling leaves is one of the most dreaded problem in rail transportation. Not only does it obstruct things very efficiently, including the passage of light, but it also makes the rail surface very slippery, making it sometimes impossible for trains to actually brake using mechanical means. Much much worse than snow or rain. One sympathizes.

French officials said the road, made of photovoltaic panels, would generate electricity to power streetlights in Tourouvre, a local town.

I don't know how reliable they are, but solar-powered streetlights are already common in some areas --- and being mounted high above on the lights themselves, the panels are far less likely to be damaged.

Wonder if that would also help reduce light pollution if the panel was wide enough compared to the lens over the light.

It was a failure but I’m glad they tried it. Hopefully something like this comes to fruition and we learn more and more with every iteration. Solar roads are a great idea. Maybe it means it needs daily sweeping with electric vacuum trucks or something but if it’s producing enough electricity then it’s worth it.

I just don’t see how it’s worth it at all compared to putting solar panels on top of buildings.

Solar panels on buildings don’t need to be as rugged, don’t need to be cleaned daily, etc, and they also can be oriented towards the sun to maximize output.

Solar roads are a solution looking for a problem. I can imagine they’d be useful to squeeze out an extra few % of output in a world where everything else is covered in stationary panels, but we’re far from that so I don’t see why we should invest lots into them were the same investment would pay much more if it was about stationary panels.

And the craziest thing is that the sunniest parts of the planet are completely uninhabited, so land is plentiful and cheap. As opposed to urban areas, which are the most expensive real estate that exists.

Urban areas are also where electricity is needed.

What do you mean by the "sunniest parts of the planet"? You mean the deserts? Not all countries have that luxury and maintenance might prove challenging, depending on the desert.

> It was a failure but I’m glad they tried it. ... Solar roads are a great idea.

It was a bad idea. Even in theory. The only positive thing about it is that it captured the imagination of lots of people who know nothing about solar or roads.

The frustrating thing was that pretty every problem that arose during these trials were already known. Those who spoke up were ridiculed for being naysayers. There's a balance between those who reflexively oppose everything and those who have an informed opinion based on experience and knowledge. There was quite a bit of overlap between those who strongly supported solar roadways and the "I f*ing love science!" crowd that have turned science into something indistinguishable from magic.

The original installation in Idaho ran into predictable problems almost immediately. The much larger installations had very little justification for going forward other than it was very popular with a rather vocal group of voters. Doubt any of the politicians, celebrities, or their fans who pushed this and dumped all over those with credible objections will apologize for their part in the boondoggle.

I'm of two minds about what you're saying. On the one hand, it looked like a bold failure from the start. On the other hand, it put the idea of solar generation in "unorthodox" places into the minds of normal people and city planners alike. Solar roads aren't the way to go - but how many people, having heard about the project, encouraged their city to put up solar panels on all the light & phone poles? How many people have taken the enthusiasm from this project and looked to see where they could safely generate power from secondary sources in their own lives?

So it's a great idea, and it's also a massive and fairly obvious failure at the same time. The message to take away from this isn't just "solar roads were a bad idea". It's that "solar roads are a bad idea, but we should keep looking at other ways to safely generate the energy we need around roads and urban passages."

The only positive thing it did for me was kill my faith in humanity. The fact that this type of thing had enough credibility to get public money indicates an absurd level of failure in critical thinking.

I think putting a roof on streets (on a relatively light aluminium/carbon fiber scaffold) for the panels is less outlandish than trying to fix "solar roads" by adding maintenance vehicles (or solar roads themselves, really).

It keeps away rain (which improves driving), doesn't expose the panels to the weight of tractors, has similar safety properties (the panels need to react quickly on any accident related impact and isolate affected circuits to avoid electrocuting passengers), and if slanted, is somewhat self-cleaning in wind or rain.

I agree though that it's nice that somebody did a field test. That idea sprang up again and again and it helps to have some real world data: people anticipated the cracking issue, but who argued against solar roads because of leaves killing the efficiency?

> but who argued against solar roads because of leaves killing the efficiency?

I had my concrete driveway pressure washed recently. It looked really good for about a week. Then leaves fell on it, and the leaves stained it brown again.

All the engineers had to do was look at flat concrete.

concrete is a permeable material, solar panels not so much.

If you coat your driveway with a resin cover, the stains will probably disappear every time it rains.

But nevertheless, it wasn't a talking point before - of course, with enough observation you can think of all possible failure modes beforehand. Sometimes it's easier to just try things out.

But anyone who has read a book about designing a home solar system can tell you that all of the literature tells you that you have to pick the location of your panels carefully so they aren't occluded by trees over part of the year because the power losses due to occlusion are significant and can make a system non-viable and non-economic. From the book I read [0] (although mine is the 2015 edition), not planning for obstacles is the #1 reason solar power system designs fail.

I'm not sure why they didn't hire an experienced engineer for this multi-million Euro project.

[0] https://www.amazon.com/Solar-Electricity-Handbook-installing...

> because the power losses due to occlusion are significant and can make a system non-viable and non-economic

That depends on how large the individual cells are and how they're wired up. There are panels that have a pass-through if they're occluded too much to avoid them limiting the output of other cells. It's possible that these panels had compensation mechanisms built-in.

> I'm not sure why they didn't hire an experienced engineer for this multi-million Euro project.

This isn't a few amateurs getting a construction grant and slapping the cheapest off-the-shelf panels they could find onto the pavement.

The panels were built by a French company called Wattway, a subsidiary of Colas, a large French street construction corporation. The parent company also did the construction work of actually putting these things on the street.

Apparently the "Institut National de l'Energie Solaire" was involved in this project as well, which is a public research facility (co-run by a university and the CEA, which has a budget of more than 5 billion Euros, and has a staff of 19k employees and 1200 grad + post-grad students).

That "solar road" might have been part of a research grant for all kinds of PV developments and they had to deliver it as a demonstration. That would also explain to me why they give up so easily. From the article: "Wattway [...] told Le Monde that it would not be going to market."

Or they could have just left a square meter outside on the ground for a few months to see how it did. It would have saved millions of dollars.

I'm sure if we invested vast amounts of money into specially curved road surfaces we could make square wheels work[1]. That would still be dumb when compared to round wheels.

The problem with solar roads is it's plainly worse than the obvious alternative: putting solar panels next to roads, or above carparks.

And innovations that made them more plausible as a road surface are also going to make for a better regular road surface, or a better mounted solar panel.

[1]: https://www.youtube.com/watch?v=MQ8PPEKROz4

> It was a failure but I’m glad they tried it.

Maybe next they could design an airplane out of bricks. Or try using water as an automobile fuel. Or that silly experiment where they tried to make a jet fuel that wouldn't burn:



It was a failure but I’m glad they tried it.

I'm not. Research funding is very much a zero-sum game. Because they spent that much money trying something that stupid, it's safe to say that some actual good ideas either didn't get funded or had to make do with less.

we learn more and more with every iteration

There was nothing to learn here. It was easy to predict the outcome based on well-understood models, and countless people did.

I'm all for trying things out, but this idea was always pretty crazy. It sounded nice at a very superficial level. Good solutions usually solve multiple problems, and this "solution" combined some problems... Seems like a smaller trial would have been just as effective

Why is building PV panels into the road better than putting them next to the road? Or in giant empty fields along roads?

Because minimizing ground covered with man-made stuff is a goal worth chasing. Leaves more of that thing called "nature" intact and doing its job, which - among other things - is to keep us alive and breathing.

Hence the idea of dual-using those insanely large areas covered with concrete that we use as roads is a great one in principle. We do the same with rooftops already, and it works great. But roads appear to be much more challenging than rooftops.

Some quick searching reveals various estimates of 1.6% to 0.7% of the US being paved over. That's including parking lots and cities, places that probably aren't good candidates for solar roads anyway.

Seems like you might get greater benefit by sacrificing yet a little more of that thing called "nature" (never heard of it before, thanks for sharing, TIL) and realize actual benefit than using the same amount of resources to solarize roads for a fraction of the benefit.

So I stand by my question.

> Solar roads are a great idea.

But why?

There are plenty of arguments against it and hardly any in favor?

> The French minister for energy said she wanted to have solar panels on one mile of road every 621 miles in the country within the next five years.

You can still do that! Just put them on a rail off to the side, angled to get lots of sunlight.

Why wasn't that strip of land right by the road converted into a solar strip instead? It looks like that shoulder has almost as much physical area to it and would take a lot less wear and tear.

I never understood this idea to begin with.

I think the idea was to take advantage of land that cannot be used otherwise.

Most roads are in rural areas with plenty of room next to them. The inventors were very aware of this, being from Sandpoint, Idaho.

As was foretold. This is all very, very simple.

Solar panels above heavy vehicle traffic: Good Idea.

Solar panels below heavy vehicle traffic: Bad Idea.

If you want to solar panel anything more heavy duty than a bike path, make a roof.

Does anyone but me have the suspicion that the animosity towards solar roads was something to do with a 'nerve being touched', some kind of 'triggering'? Sure, they might not work out, but lots of stupid-sounding ideas ('a horseless carriage? Whatever next?') have turned out to work, just as much as lots of somewhat futuristic but nonetheless sensible sounding ideas have turned out not to be here yet ('flying cars are just around the corner'). Who knows, at some point in the future, with different technologies and materials, different efficiencies and performance, we might indeed find solar energy being collected from roads. Just as we are laughing right now at the current, ludicrously oversold and patently unsuccessful efforts, future generations may be laughing at our arrogant dismissal of an idea that might ultimately have just turned out to have been ahead of its time. Let's applaud the audacity of the solar roadways hubris in the spirit of uninhibited innovative endeavour, just as much as we pat ourselves on the back for having successfully spotted its obvious shortcomings and predicted its seemingly inevitable struggle for survival.

It touched a nerve with engineers because nobody listens to engineers and they’re getting completely sick of it.

Engineers are paid to work things out on paper and determine whether something will work or not. Bridges, airplanes, power distribution systems, those kinds of things. They don’t use arrogance, they use math.

This isn’t particle physics - there are no “unknown unknowns” here that required a real world experiment. The economic infeasibility of solar roadways was an absolute slam dunk case.

So now we have confirmation that it was, in fact a bad idea all along. What’s the reaction? “Well, nobody could have predicted this! We had to try.” No, you didn’t have to waste all that money, you could have just listened to competent people in the first place, who all predicted this.

I mean, excuse the hyperbole, but you may as well applaud the audacity of launching Challenger in temperatures below the booster o-rings’ rated spec. Who knows? It could have worked!

>Sure, they might not work out, but lots of stupid-sounding ideas ('a horseless carriage?

It's a monumentally stupid idea. I'm surprised it isn't outright labelled as a scam. They basically cheated money out of governments and gullible people with a project that was never a good idea in the first place.

Solar is the perpetuum mobile of our time.

Yeah I don't know why the article is so negative. Any engineer would look at this and say, "cool, a few more problems to solve" not "well golly, I guess there's nothing we can do about a few leaves".

Like placing the panels above roads, for example. It helps to get optimal inclination of panels too, and reduce stress levels, and eliminates losses from cars' shadows, and simplifies maintenance, and reduces pavement costs.

Some ideas are just plain stupid.

It is the dumbest idea to use a solar road when there are roofs; like bus shelters. train stations or even sound walls that can be converted. Cars would literally rip these roads apart due to dirt and grind.

Even EENblog made several videos about this in the last few weeks. Just have a look:

* https://www.eevblog.com/2019/08/07/eevblog-1233-the-demise-o...

* https://www.eevblog.com/2019/08/07/eevblog-1234-more-epic-so...

* https://www.eevblog.com/2019/08/18/eevblog-1236-german-solar...

There was a fairly ridiculous promotional video going around YouTube circa 2014 about a couple who “invented” solar roadways. I’ve placed a link here for your amusement.


Yes, solar roads were always the answer to the question of "where is the absolute worst possible place to put solar panels".

This was 100% predictable.

Could be worse.[1] Remember the schemes for recovering energy from traffic on sidewalks and roads?

Pavegen pivoted to collecting info about people walking on their sidewalks, rather than energy.

[1] https://pavegen.com/

>Pavegen pivoted to collecting info about people walking on their sidewalks, rather than energy.

Wow. Switching from saving the world, to spying on everybody in it. That's almost a perfect microcosm of how the tech industry seems to have morphed in the last decade.

The four stages of technology:

- innovation

- productization

- marketing

- milking IP

Ouch, yeah, that's pretty bad. I've actually been at a fair number of events with these folks, as my own startup often gets put into the same bucket with them (also London-based and associated with "green" transport infrastructure). I've always avoided having a conversation with them, because it just seems so ...sad.

As a straight-up marketing device -- say, a way of creating some interactivity at your storefront in order to get people to linger there longer -- then I guess it's fine, or at least no worse than any number of other things. I actually find that less objectionable than painting it with a green "we're helping to save the world" veneer that is either very cynical or very deluded. It takes a trivial amount of cognitive effort to understand that energy recovered from footfall will never, ever, pay back the embodied energy to produce and install the device. (Even moreso if you include the metabolic efficiency of human power in the energy calculations). This shouldn't be hard to figure out: it was pretty well understood by the end of the neolithic. But I suppose people are capable of remarkable feats of mental gymnastics.

Talk about ethical whiplash. I feel especially bad for any engineers that joined to make the world a better place then found out they would be designing tracking systems...

Yeah it sure would be awful if that happened to anyone. Imagine joining a company that claims to help the world and instead you design unbelievable tracking and surveillance systems. Ha ha. Ha. sobs

Yeah, like welcome to tech.

"recovering energy"

I can think of worse places. On top of airliners, for example, or inside active coal mines.

Under airliners seems even worse.

I know, put them on the turbine blades.

Anyone who bothered doing the math knew this was a horrible idea from the very start.


For those who don't watch him, EEVBlog has had excellent videos on the feasibility of solar roadways.

To summarize his videos: solar roadways were never feasible even in theory with quick back-of-the-envelope calculations and all of the known solar roadways projects in the world have failed or are nearing failure.

I can't imagine how hard it must have been, in France of all places, to try something that bold and risky and obvious to oppose beforehand.

We're the country of ruthless self deprecation coupled with perfectionist universalism.

I hope something was learnt here (other than learning not to do it again), and I'm absolutely confident the people who cluelessly pushed for it will go on their public careers unaffected while the innocents are punished.

We've done more insane stuff and survived to tell the tale.

But really, PV in Normandy ? Come oooooon....

>I hope something was learnt here (other than learning not to do it again)

I'm afraid not - the trials played out exactly as the naysayers predicted. Most of the panels cracked under load and failed due to water ingress; those that didn't became woefully inefficient due to soiling. They were dangerously slippery even in ideal conditions, they cost much more than a conventional rooftop installation and they never generated as much electricity as a rooftop installation even when they were brand new.

The whole exercise was a complete waste of time and money.

> We're the country of ruthless self deprecation coupled with perfectionist universalism.

I wonder if there traits make you good at nuclear power. Perfectionism and ruthless self criticism seem like they'd engender the kind of thorough and methodological approach that keeps reactors from getting explody.

The Russian "can't duck it, fuck it" attitude seems to have the opposite effect judging from the Geiger counter readings.

French arent afraid to be weird. Let me introduce you to Renault Twizy - a road legal mobility scooter, and Avantime - the only coupe minivan even made, a 2 door with no B-pillars, sold as good as that description sounds.

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