Why solar roadways won't work

Why solar roadways won't work

Why solar roadways won't work

JeffreyR | June 8, 2014

I think it is healthy, even vital that we attempt to better understand how Solar Roadways is expected to work and question their work. The thing to remember is that this has been a project for several years. Several third-parties have collaborated with them including several university material scientists who have figured out how to make "glass" that meets their requirements for building the Solar Roadway.

The main goal is to improve the roads, not just to generate electricity. So folks that say, "they should do roofs first" misses the point. They are using de-centralized power generation & transmission, engineered "glass", LED lights, heating elements, water treatment, and a "cable corridor" to improve how we build roads. The current roads need to be maintained, so there is existing budget for that purpose.

Check out Samuel Simon's well reasoned reply to this nay-sayer video.

The founders of Solar Roadways are actively responding to posts on Indiegogo, so if you have questions that are not covered in their FAQ (which is constantly updated), that's the best place to ask them.

Timo | June 9, 2014

Whole "better road" fails in one critical point: it is insanely expensive. Both maintain and build. That makes all the rest of the points moot.

Maybe for small scale, like parking lot, but as roads, never. Just plain too expensive.

Detroit SuperCharger | June 9, 2014

+1 JeffreyR. All great points.

Additionally, the Brusaws have setup a to rebuke common statements like "they're too expensive"

@Timo : The FAQ covers, very specifically, the concerns you mentioned.

Detroit SuperCharger | June 9, 2014

a *specific page to* (^looks like that link didn't do quite what I wanted it to)

Dramsey | June 9, 2014

The "well reasoned reply" makes a lot of statements like this one:

The glass surface in question has been tested for wear, load, impact resistance, ability to stop a vehicle traveling numerous given speeds in the required time (the "stop tests" you seem so indignant about,) and everything else a concrete/asphalt surface is required to provide; the glass and texture being used are a product of materials research and have been tried, tested and true for years now..

So I looked at the FAQ and it says:

We backed off a little and ended up with a texture that can stop a vehicle going 80 mph in the required distance.

Really? How did they determine that? Obviously not by driving a vehicle at 80mph on a test stretch of road, because that doesn't exist. So it was simulated. What was the weight of the simulated vehicle? What kind of simulated tires? What, precisely, was the "required distance"? And has it really "been true for years now"?

I don't think there's any way they can make claims like this without real-world testing.

Timo | June 10, 2014

FAQ doesn't cover my concerns. I looked. It just makes unproven claims and has lots of misinformation.

"Years ago, when we were working on our very first prototype, we estimated that if we could make our 12' x 12' panels for under $10K, then we could break even with asphalt."

Um, how? 12' x 12' section of asphalt costs about 0.001 dollars. That's million times more expensive. How an earth that would make it "break even"? Material costs for asphalt roads are microscopic.

That's about 13m^2, if you have around 10% efficiency and get 6 hours of useful sunlight that's 7.7kWh / day. That costs about $0.77.

$10k/$0.77/day ~= 13000 days or about 35 years. That's just for panels. It doesn't include increased infrastructure costs, increased worker time costs, increased maintenance crew education costs etc.

"removal of snow" by heating is just moronic. If you try that you use way, way more energy to do that than you would produce energy by those panels in hundred years negating the very reason to have those.

FAQ has this line:
Each year, 24 percent of weather-related vehicle crashes occur on snowy, slushy or icy pavement.

That makes 76% that doesn't happen on snowy, slushy or icy pavement. IOW snow/ice doesn't increase accident rate, or if it does it is small increase.

That FAQ doesn't even touch the biggest problem: thermal expansion. That's what breaks the roads as flexible as asphalt. These things are rigid. Does it use some sort of flexible seams? How do those handle traffic?

It doesn't cover time to construct the road.

Or what happens when one panel breaks off from the road. You have serious sharp-edged surprise hole into road almost certainly leading to serious accident. Loose panel also might get airborne making that another factor leading to serious accident.

DTsea | June 10, 2014

Good points timo.

Note though the thermal expansion coefficient of plate glass is only 5 microinches/inch/degree F. So for a 100 degree F temperature change (assuming glass stress relieved at 60 F and peak summer aurface temp of 160F) a 1 foot tile would grow 12×.000005×100 or .006 inches. So a .012" joint gap would handle it. Pyrex and hard glasses have even lower thermal expansion. Glass has a much lower CTE than concrete, which for atructural concrete is about 9.5. Plain concrete is about 14. Difference is the steel reinforcement.

the solar road is a silly idea but not fpr the thermal expansion.

Detroit SuperCharger | June 10, 2014

Certainly there are questions to be answered and problems to be solved with this new tech. However, consider these three simple points :

1) The Wright brothers were called "silly" and told "man will never fly". Even one of the brothers themselves had his doubts.

2) "The horse is here to stay, but the automobile is only a novelty—a fad." - Advice from a president of the Michigan Savings Bank to Henry Ford's lawyer Horace Rackham. Rackham ignored the advice and invested $5000 in Ford stock, selling it later for $12.5 million.

3) Here's the most important (to me) : Elon Musk himself, believes that Solar Roadways are feasible, as he donated to the cause, as did Bill Gates (they're probably 2 of the 11 donators that bought one of the functioning models for 10k a piece)

* Not to mention a little entrepreneur of electric cars and space travel, who of course was told time and time again "An electric car that gets over 100 miles is not possible right now." Then when he proved the world wrong. They replied by saying "Ok. Sure. You can build one. But people won't buy because it's won't ever be affordable". He proved them wrong again. And where is THAT guy today? :)

Past examples of "it can't be done, and then it was done" aside, it is Elon's tacit endorsement (IMO) that holds more weight concerning the feasibility of this tech, than any argument for or against it.

Is there a possibility of it failing? Of course there is. However, is there enough possibility of it succeeding to try? I believe so. But my opinion is moot. The important part is, I believe that Elon believes it's possible.

Now, I am no engineer, and cannot argue specific points, at least not ones that haven't already been addressed by the Brusaws regarding feasibility. I am, however, smart enough to know this one simple thing : I am not smarter than Elon. Are you?

AustinAnthony | June 10, 2014

I am surprised that Tesla supporters would bash a bold concept of generating electricity from solar roadways. Right now some of the answers are unknown and obviously the current prototype system can be vastly improved beyond what is even conceived by its inventor. Engineering from many disciplines is definitely needed and each product iteration will increase efficiency, lower costs, and improve wear-ability, serviceability, and all other metrics associated with its performance and cost.
This nation currently spends hundreds of billions every year for electricity. We also spend tens of billions on maintaining our national highways and over 12+ billion more on solar arrays. All these cost are increasing annually. Combined, this is over half a trillion dollars every year. I am sure to replace our national road with solar panels will cost trillions, but what is the threshold for the break even?
Five-years, ten-years, 20-years?
What is the current break-even for a solar array on your roof without including government incentives? It is probably between 10 to 20 years, but it gets better every year with lower cost and better efficiencies.
In my opinion, this is a product worth developing and putting in parking lots and driveways for commercial and residential customers. This market would pay for further development and one day we may be driving on solar-freakin-roadways and wirelessly charging our Li-Air 1000-mile batteries with the electricity coming from it. Sounds like a cool solution to me.
Let us not forget that this nation put a man on the moon 45 years ago with less computing power than your smart-phone. We are a nation of inventors that dare to dream of a better future. This is a defining American trait and has propelled us to be the world leader.

DTsea | June 10, 2014

1- that is a myth. Men had already flown in gliders. Propulsion and stability/control were the needed breakthroughs.
2- I wouldnt ask a bank president about technology trends.
3- If you have $8B i guess a token toss to every green wild idea is ok.

Detroit SuperCharger | June 10, 2014

@AustinAnthony : Exactly. +1

1) Not sure that's accurate, but even if it is, it's just semantics . . . insert "Propulsion and stability control" into the quote / sentiment.
2) All right. Use the naysayers against Tesla as an example then
3) Token or otherwise, I don't believe he would tacitly endorse an idea with THIS much momentum in the viral / social landscape if he didn't believe it's possible, as I'm sure he's aware of the weight his support would carry.

“If we worked on the assumption that what is accepted as true really is true, then there would be little hope for advance”
- Orville Wright

Iowa92x | June 10, 2014

Solar roads = bad idea
Transparent solar panels in place of windows on high rise buildings = good idea

AquaponicsOnMars | June 10, 2014
they raised 2 million so far in donations,
lets not hate on this new great idea
Check out this video on YouTube:

please watch and learn what these amazing real government funded things can do
before this forms goes hating on a new idea , a new idea like the electric car,a new idea like the solar module but better
learn the facts please,
my tesla is not a snow plow , so if solar freaking roadways produces lower and keeps my roads melted and safe then why not save lives!
and the couple who made them are very nice, if you hate on solar freakin road ways then you
might be a bully who hates new great ideas that can save lifes and
create clean renewable sustainable power, also solar modules on a house don't work when covered with ice and snow

AquaponicsOnMars | June 10, 2014

produces power*^

DTsea | June 10, 2014

Detroit Supercharger,

my bachelor's and master's degrees in aeronautical engineering included careful instruction in the history and development of heavier than air flight.

Google "otto lilienthal' to see manned gliders in the 19th century and 'samuel langley' to see attempts at powered flight with steam engines where every interested observer realized that the power to weight ratio of steam propulsion was too low. Also you likely enjoy the Wright Brother's diary. It is a fascinating read (also a nice audiobook) in their own words. They discovered that published airfoil data was incorrect by redoing the airfoil lift and drag curves with their own wind tunnel.

I offer this to you not as a 'neener neener' but because I think you (and everyone else) might enjoy reading about another key invention that required the confluence of several related technologies.

No one thought that stability and control or heavier than air flight was impossible. They could see birds flying... they weighed them.... they just knew they didnt have all the pieces to make a powered glider big enough to carry a man. Noone said electric cars were IMPOSSIBLE either. They just thought they were IMPRACTICAL which is a very different animal.

As to the solar roads... no one here is saying that an embedded solar panel in modular blocks can't work (in the sense that it might be strong enough to hold a car, and might generate some power). Rather I would say it is IMPRACTICAL because the FAR SIMPLER solution would be to erect ordinary solar arrays NEXT to the roads. That is an existing solution. The airplane metaphor doesnt apply because there was no existing solution to the problem the early aviators were trying to solve (although lighter than air flight persisted into the 1940s and there is still a small aerostat industry today).

Timo | June 11, 2014

@DTsea, about thermal expansion, I have understood that glass is only surface of that thing, underneath of it is electronics and other stuff that is fixed part of the whole. While glass expands only slightly, what happens to all of that? If there are seams (like I asked) how durable are those?

A joint gap every few feet would put the underlining structure in huge stress. If you make that strong enough cost of that probably doubles the cost of the thing.

DTsea | June 11, 2014

timo, i am assuming that a glass surface thick enough to carry vehicle traffic would dominate the thermal response, and that electronic modules would be isolated from the mechanical load path.

AustinAnthony | June 11, 2014

Who is to say that this invention will not morph into a thick multi-layered engineered-film applied to existing roadways surfaces with the photovoltaic cells and the electronics all integrated and protected by a transparent nanoparticle film and using carbon nanotubes for additional rigidity and for storage and distribution of the energy. As Americans, we spend over one trillion dollars a year for our gas and electricity alone. There is a huge market for this product and once we are all driving Teslas, our total electrical energy demand will more than double, if not triple. I prefer to invest in ways to reduce our nation’s dependency on fossil fuels and foreign energy resources. Anybody have other ideas to further this endeavor?

Detroit SuperCharger | June 11, 2014

@DTsea, I appreciate you expounding on your reply and creating a thoughtful exchange. Allow me to do the same. Following the line of thought around existing vs non-existing solutions for problems, as well their practicality, consider the second paragraph of the first reply to this thread by JeffreyR

The main goal is to improve the roads, not just to generate electricity. So folks that say, "they should do roofs first" [or windows] misses the point. They are using de-centralized power generation & transmission, engineered "glass", LED lights, heating elements, water treatment, and a "cable corridor" to improve how we build roads. The current roads need to be maintained, so there is existing budget for that purpose.

If the goal was simply achieving as much solar powered electric generation as possible, I would then agree with you - there are better existing solutions. However, Solar Roadways is NEW (non-existing) solution to a confluence of multiple problems.

Regarding their practicality, I believe that economies of scale through production refinement alone could be enough to justify their cost and make them practical (similar to the production of the Model S)

However, we do not have to consider economies of scale and production refinement alone -

1) Job creation (in multiple markets - manufacturing, installation, software, etc), this is where the horseless carriage / automobile analogy would be useful. Jobs weren't lost, industries were shifted and jobs were created.

2) Zero vs Some : There's zero return on current roads.

3) Longevity : I have watched the same stretch of highway, be replaced about every 4 years for almost my entire life. If Solar Roadways really could last for their targeted 20 years before needing servicing/replacement. That would be astounding.

4) Safety : Saving lives, preventing accidents, dynamically directing traffic, these are all amazing innovations.

5) Power distribution : Eliminating brown/black outs in my area would be a godsend. I literally have the power go out, for several hours about every other month, especially in the summer though.

6) Eliminating dirty power : Coal, nuclear, and all other horribly wasteful methods of power production

7) Snow melting : I know this means nothing to most of the country, but living in the MItten, I LONG for the day where snowplows and salt trucks are as useful as milkmen and ice delivery trucks.

The list goes on (really, ^that's^ only a fraction of their potential functions.

If Solar Roadways only intended to be a source of energy creation, then I would also find them to be not practical. But they are not. And while for all of the above problems, there are indeed existing solutions, they are all tackled individually, and very poorly, and a great cost. It is for those reasons, that Solar Roadways is a NEW solution, because it is a multi-solution.

Pursuing them for only one of their features is definitely impractical. But for any 3? or 7? or 12 of it's features? It becomes amazing. It's like if Rogue touched 21 X-men at the same time :)

In a hundred years we've only seen a sliver of improvement in our road production methods. This could have world altering benefits to an even larger degree than the creation of the highway system.

From my perspective, Solar Roadways may very well become a Green Silver Bullet, to not only save our planet, but our economy too, not to mention the positive health benefits.

BTW, I do love history, especially as it pertains to inventions and technology. Hope to carve out some time to look into your recommendations.

Detroit SuperCharger | June 11, 2014

REALLY wish we could edit posts. Ah well. Here's a quick test to see why my blockquote and bullets didn't work . . .

test bq


Detroit SuperCharger | June 11, 2014

Damn it! One more try then I'll stop

test quote


DTsea | June 11, 2014


I hear your point that the vision is attractive. I agree.

I just dont believe the hardware solutiob proposed will realize that vision both because of its high cost and due to impracticality.

Take snow melting. Heat of fusion of water ice is 334 kJ/kg. A kg of ice is one liter of water. A ten cm snowfall is equivalent to 1 cm of rain which is 1000 sq cm per liter or 0.1 square meters. 1 square meter is ten liters... 3340 kJ of heat. Typical road lanes are about 4m wide so for a two lane road plus shoulder about ten meters which is now 33400 kJ. One kilometer of two lane road with a 4"/10cm snowfall then requires 33.4 GJ of energy.

To clear that in 1000 seconds (20 minutes) would require 33.4 MW of power.

Given an average 1 GW nuclear power plant, it could clear 90 km of two lane road per hour, flat out. Assuming your town is 5 km square with 12 blocks per kilometer yields a total road length of (5×12)×2 or 120 km of road. So the nuclear plant could do it in 80 minutes if ALL the energy could go to melting the snow. 2/3 of power is lost in transmission and conversion and the heaters will have to heat the bricks first so it's probably more like 6 to 8 hours.

Of course that requires shutting the power down for that time.

easier to just use a snowplow. 6 plows at 20 km/hr could do it in an hour.

Note the solar road doesnt make any power when covered with snow.

DTsea | June 11, 2014

.you can use an electric tesla snowplow if it makes you feel better.

Takes a lot of power to melt ice.

Brian H | June 11, 2014

Getting to the "economies of scale" would require losing trillion$$ in build-out sunk costs along the way. Not happening.

Detroit SuperCharger | June 12, 2014

@DTsea, appreciate the technical breakdown. On all engineering fronts, I only know enough to defer to those that know more than me. From what I see here, the heating element numbers have not yet been directly addressed in detail. I expect they will be as soon as they have the opportunity to do so.

@Brian H, as far as I'm aware, there are not yet hard numbers to extrapolate cost. More over, if the creators of this tech are uncertain of the cost at this point, I do not see how any one else could be.

It could very well be that the initiative fails, at least in it's current form. For me though, knowing individuals such as Elon and Gates believe in it enough to contribute towards the fund (wildcard that it still is) is enough for me to hold onto hope.

As with all new things though, to each their own. Underdogs and improbable goals have succeeded in the past. I believe this may very well turn out to be another example of that.

At the moment, I am only certain of this one thing - to claim certainty for or against the feasibility of Solar Roadways is to claim to know the future. And that, is the only thing I see here as entirely impossible, even if you guess, and you're guess is right - you never knew. So, we'll see . . .

AustinAnthony | June 12, 2014

Let’s not get wound up over the “potential” costs just yet, or if it will melt snow. Over a trillion dollars have been spent in semiconductor R&D over the last 50 years and another trillion will be spent in the next 15-20 years. That is only for R&D to manufacture smaller/faster/cheaper semiconductor chips! This was possible since there has been an ever growing market demand for better performing chips. No one knows what market trends and technologies will dominate the future. Did anyone predict Tesla, Apple, Google, Facebook, or even the power of the internet 20 years ago? We need to continue to invest and develop many solutions as alternatives to our current dependencies on fossil fuels and let the market decide which one is best. Maybe cold fusion will be the answer.
We already have spent tens of trillions of dollars to support various industries that revolve around extracting oil from miles below the ocean floor and shipping it half-way around the globe to be refined and transported to people so that they can fuel their vehicles, all while wasting over 85% of the energy content and pumping billions of metric tons of exhaust into the air every year. There has to be a better global solution to how we power our transportation and Tesla is just one company. Tesla may be the seed company that drives market demand to EV’s and this in-turn propels the development of new industries to support EV’s with renewable electrical power. Solar-Freak’in-Roadways is just one possible solution, but I am sure there are and will be many solutions and they will compete for market-share through pricing and this will lead to increased innovation. Maybe we will have the "flux-capacitor" in cars of the future.

Red Sage ca us | June 13, 2014

AustinAnthony: Agreed. I for one have been wanting a Mr. Fusion for nearly three decades now. ;-)

aeroscott | June 15, 2014

Behind the house I grew up in is a alley of ceramic glazed brick. It's well over 100 years old and still in great shape . It's seen a lot of heavy trucks and traffic over time.
Heat pipes can do snow removal if necessary.
I was a member experimental aircraft association and one of the big problems is the nay sayers , According to the experimenters.

JeffreyR | June 15, 2014

@AeroScott that's the first example I've seen on this forum of a real-world example of how tempered glass (ceramic glaze in your example) can be tough enough to last. Admittedly the material scientists working with Solar Roadways Inc. already believe they have that issue resolved technically if not practically/economically. I really appreciate your post.

Question: can you post pictures or info about those glazed bricks? I think folks would be interested in seeing more. See my or T.J's posts about Tips & Tricks on how to include images. Quick-and-dirty way is to paste a link to a page w/ pics/info on it.

Thanks again!

Dramsey | June 16, 2014

@Aeroscott: How certain are you of the alleyway's age? Granted, any existing brick road will be old; but even if the bricks can last a century, one would expect settling of the road bed, plants growing up between the bricks, et cetera, leading to cracks and whatnot.

Of course an alleyway gets only a tiny fraction of the traffic a surface street would, so at best this is an interesting anecdote, since we can only guess at the load-over-time.

That said, your point about naysayers is well-taken. As Heinlein notes, one can assemble a history of science in reverse by taking the most solemn pronouncements of the highest authorities that thus-and-so is impossible and will never be achieved.

(Of course, most of the time, they're right, but there are those spectacular outliers...)

aeroscott | June 16, 2014

I'll get some pictures together . The house has been in the family back to my great grandfather. I met the women who's family lived in it first,I was a kid{ 16) in about 1970 she was in her 70-80's
Lt's in Milwaukee,Wi.37th st.and Brown 5 blocks north of Harley Davidson. Davidson lived across the street.
Dad grew up and lived in the house 1918 to 2005 was a metallurgical engineer with A.O.Smith, attempted a ev in 1960 with Smith, BMW and Wisconsin power . Smith opted out, Dad lost his senior engineering position and was demoted to junior engineer for the next 20+ years over this. He was told they worked for GM and they would not like this.He was later promoted to senior and worked on many interesting projects
On the longevity, the conventional alleys in the area have been resurfaced/repaired many times. I think this is do to thermal stress more then load stress. No apparent thermal stress on the brick. The bricks are 2X thicker then conventional and smooth glazed and very dense. There is some settling which is best seen at night with headlights.

abebarker | June 18, 2014

I've done some thinking about solar roads myself. I think solar roads could be an excellent idea with some caveats.
Photovoltaics are impractical to embed in a roadway for several obvious reasons.
1) Roads are dirty. The amount of grime that accumulates on the surface of a well use road way will block most light from penetrating.
2) Silicon solar cells are expensive.
3) Silicon solar cells are inefficient.

The one thing that most current roads have going for them is that they are black. A black body is the most efficient solar collector.

Heat is the best way to obtain solar energy from road ways. Unfortunately it is a low grade heat i.e. the temperature difference from ambient is rather low.

The cheapest and most practical way to obtain solar energy from a roadway is to embed piping within it. Use an appropriate engine, one designed for low temperature. (Example: ORC Waste Heat Turbine)

Heat pumps can be used as a regenerator if the efficiency of the engine is greater than the inverse of the COP of the heat pump. Great care must be taken in this case so as to not remove too much heat and ice over the roadway.