Solar Roadways has been in the press recently about its first deployment of panels in a pedestrian area as a proof of concept. Proponents promise abundant solar power and better infrastructure. Skeptics, however, insist that these are expensive projects that ignore basic tenets of engineering. Are solar roads a disaster in development?

Alternative energy sources have seen a decrease in price over the last few decades, with arguably the most promising power source of the future being solar energy. Back in 1954, Bell Labs produced the world’s first practical solar cell with a 6% efficiency which started the race for solar energy. Now, solar cells can be as efficient as 30%, as demonstrated by engineers at the University of New South Wales, and manufacturing techniques have made them considerably cheaper than in years past.

The prospect of using solar energy as the energy source of the future has been taken seriously by many engineers and inventors alike. Tech companies such as Tesla have invested in inventions like solar cell roof slates and lithium-ion batteries to store power and release it upon demand. But several companies and thousands of everyday people have been supporting a new use of solar: solar roads. 

 

The Roads of Tomorrow

A solar road is a concept where solar panels are embedded into materials used to either replace or rest atop of pathways and roads. There are several major solar road projects presently being developed and/or tested, all sharing the same core principle of roads that collect solar energy.

The first solar road to be implemented, "SolaRoad", was a solar bicycle path installed in Krommenie, the Netherlands, in 2014. The path is 70-meter long (just under 230 feet). It cost over $3 million to install. Over the past year, this installation has yielded 9800 kWh of energy (Dutch language link). It's been considered a success and may be expanded in the coming months.

Another solar bike path was unveiled in Pruszków, Poland in October of 2016 with a hook of glowing blue in the night.

 

Image from TPA Sp. z o.o.

 

One of the only solar roads meant to withstand vehicle traffic, however, is in a small village called Tourouvre-au-Perche in Normandy, France. The road is one lane, 1km (0.6 miles) long, of solar road that opened for traffic in December of 2016. The model is called the Wattway and the current installation will remain in place for two years to test durability and efficiency. The cost of the installation is estimated to be over $5 million.

 


But the solar roadway project that we'll focus on in this article is in the USA. While other solar roads face similar challenges and criticisms, Solar Roadways are unique in their design, materials, and ambition.

 

Solar Roadways: Sandpoint, Idaho, USA

Solar Roadways (founded in 2006) has a vision where all roads, pavements, and parking lots are replaced with smart solar units that contain a multitude of features to cope with traffic-related problems and electrical generation. Simply put, imagine a modular solar system where each module contains a solar panel, battery storage, microcontroller, heaters, and LEDs. Then, replace the asphalt on roads with such modules and, by doing so, create road systems that are intelligent and positive for the environment.

 

A mockup of the Solar Roadways concept. Image from Solar Roadways

 

Some of the technical data given by Solar Roadways is given below:

  • 230-watt solar cells with 18.5% efficiency
  • Energy output for solar roadway roads up to 15.847 billion kWh (assuming all roads fitted)
  • Cuts greenhouse gas by 75% if installed

You can see the calculations used to reach that last bullet point on the "Numbers" page on the Solar Roadways website.

Roads that can change layouts instantly, respond to traffic, alert users of people crossing roads, automatically defrost, and all at the same time providing electrical power sound incredible.

But if it sounds too good to be true, it probably is. Some of the criticisms that follow are inherent in the concept of solar roads while others are unique to the ambitions of Solar Roadways.

 

Criticism of Solar Roadways

Solar Roadways promise a lot but their feasibility is dismal from an engineering perspective. It is at this point that some readers will flock to the comment section and start defending Solar Roadways as the future roadway system. Some may even make comments such as “people thought x was stupid or y was unfeasible but we made it happen”. However, true science relies on hard evidence and rational thinking. So before coming to any conclusions, please consider the following issues.

 

Problem 1 – Angle of Solar Panels

The first problem with Solar Roadways comes from the inbuilt solar panels, themselves. Since road surfaces need to be flat, the panels need to be as low-profile as possible. This means that the solar cells inside the panels are laid flat.

This isn't ideal because solar cells generate the most electricity when directly pointed towards the source of light (in our case, the sun). While the sun does move across the sky as the day progresses, every single place on the planet has an optimum solar panel inclination and orientation. For example, my hometown (Ringwood) has angles of maximum efficiency at 16 degrees during the winter and 62 degrees during the summer. By comparison, the angles for Houston, Texas, are 36 degrees during the winter and 84 degrees during the summer. More advanced solar systems use tracking mechanism to keep the solar cell constantly pointed towards the sun. You can investigate the optimal angles for solar in your area here.

Solar Roadways, however, will always be fixed pointing directly upward (or, to be more specific, they will be at the same incline as the road). Keep in mind that this is before the system has even consumed power.

 

Problem 2 – LED Visibility

The mechanism for creating road markings and information displays is to use LEDs as they are commonly associated with high-efficiency light sources. However, using LEDs in such an environment comes with many problems.

The most important issue with LEDs in this scenario is their tight viewing angle (typically ranging between 10 degrees to 60 degrees), which makes them difficult to see at extreme angles. For example, an LED pointing vertically upward is rather easy to see from above (as shown in the Solar Roadways adverts), but seeing that same LED from an angle commonly involved with driving will be next to impossible for common LEDs.

 

Image from Solar Roadways

 

There are LEDs that have much wider angles (typically by incorporating a lens). However, these are not only significantly more expensive but most of the light emitted is still beamed perpendicular to the ground. One solution would be to mount LEDs at an angle to point towards drivers but such a solution still has problems. For one, multiple LEDs would have to be used per “pixel” all pointing in different angles to guarantee that the information can be seen from all angles. The second problem is the significant increase in energy consumption. This viewing angle problem is likely why all footage of solar roadways is taken in either dark conditions or from a high angle.

The second problem with LEDs the amount of power needed to make them visible during the day. LED billboards know this struggle well: a single LED billboard can utilize hundreds of thousands of kWh of energy every year just to stay bright enough to stay visible.

See the Solar Roadways LEDs in action in the live stream of the Solar Roadways installation at Jeff Jones Town Square in Sandpoint. Visibility demonstrably changes depending on the time of day.

 

Problem 3 – Solar Panel Cost

According to the US Department of Transportation, the US has over 2.7 million miles of paved roads as of 2013. When purchasing solar panels in bulk, the price of solar panels drops to around $0.74 per watt which is $740 per kW (this is the price of solar panels that are used in residential power and not those found in calculators or low-power applications).

Using a 20% efficient solar panel puts the energy generated by a single panel at 200 watts per square meter (assuming that the earth’s surface receives 1000 W/m2) and therefore the cost of a square meter panel is approximately $148 for a meter square. With this in mind and with over 2.7 million miles of roadways to pave, the cost of the solar panels alone blasts up into the trillions. This doesn't take into account the energy losses and consumption by the modules, themselves, nor installation costs.

 

Problem 4 – Heating

Solar Roadways boasts how these roads will prevent the build-up of ice and snow which will massively benefit cold climates. However, as calculated by thunderf00t, the energy needed to melt ice is considerably more than the designers may have realized. 

 

Image from Solar Roadways

 

To turn 1kg of snow into 1kg of water requires 334kJ of energy which comes to 92.77 Watt hours. Let's say that there's 13cm of snow on a 1-meter panel. That would be around 0.013 cubic meters of snow. Assuming that freshly laid snow has a density of 100kg per meter cubed (10% water content), then the total weight in kg of snow on a 1-meter square panel is approximately 1.3kg.

Therefore, the minimum amount of energy to melt the snow (keep in mind that this is from 0°C ice to 0°C water) is 434.4kj or 120.6-watt hours. With solar panels that obtain 200 watts per square meter in the best of conditions (which winter is not), the spare energy is around 80 watts. This does not consider the power consumption by the LEDs, power converts, or any circuitry.

If snow falls at a temperature lower than 0 degrees then the energy increases. If the snow was -10°C and it has to be raised to -1°C (just before it melts), then the total energy needed is 18.81 J per gram which would correspond to 7 watts of power (which takes you from 80 watts to 73 watts of free power left). 

 

Problem 5 – Maintenance Costs

One argument for Solar Roadways is the sheer number of engineering jobs that it would create. This particular point is spot on because maintaining such a system would be incredibly difficult, if not impossible. Assuming that a panel has a lifespan of a typical solar cell (which is very generous to assume, due to the unforgiving environment they are in) of 20 years (the time until 80% power output is reached), then the entire road system would need repair every 20 years which puts the average cost of the project at $1.15 trillion every year—and that's only calculating for the replaced solar cells, excluding workforce costs.

But this assumption relies on all the panels working til their end of life. What about individual panels that get broken? Considering the number of panels needed to be implemented (1.57×1011 where each panel is 1-meter square), a failure rate of one in a million still results in 1,570,000 panels needing to be replaced within that failure rate time.

 

Problem 6 – Wear and Tear

Roads are made of asphalt for a reason. It is a cheap, widely abundant material made of oil industry by-products and pieces of stone. The surface of Solar Roadways is to be made of glass which, in itself, contains many problems not yet addressed, including the danger of glass dust if damaged tiles are crushed.

How long a glass surface would last has yet to be determined but heavy traffic would quickly bring the surface of the glass to bear. Even if this is not a problem for the road, itself, it is a very big problem for the solar panels under the glass. For the panels to work at their maximum efficiency, the glass must be as optically transparent as possible to allow light to fall onto the panels. However, scratched glass has a horrid tendency to diffuse light and send it in random directions which reduces its optical transparency and hence impede the solar panel's ability to generate electricity.

But this optical transparency has a more devastating potential that has not been considered.

 

Problem 7 – Glare Safety

Safety is perhaps the most important concern and the danger lies in the glass. If the glass is toughened and has a cloudy look to it then the electrical output of the panels will be reduced. So, to get around this, the panels use clear glass to allow as much light through as possible. However, this leads to a very dangerous situation that occurs when the sun is low in the sky.

Light from the sun (when it is low in the sky) will hit the panel at a low angle, reflecting light like a mirror or a puddle on the road. This means that entire roads will reflect morning and evening light up into drivers' eyes and potentially cause accidents.

 

Image from Solar Roadways

 

Solar Roadways Now

Despite these shortcomings, the Solar Roadways project continues to receive government and Indiegogo funding. The system has been demonstrated in several places including a driveway and the first public installation of Solar Roadways found in Sandpoint, Idaho. However, the Solar Roadways system began to show signs of failure days into its operation with most panels non-functioning within two weeks of installation.

More importantly, the reveal of the installation was rushed and flawed, meaning that the panels were able to "provide a light show" according to Scott Brusaw. "The solar cells and the heating elements are unusable in their current state.”

A website was supposed to be created to show live energy production from the system but the website address does not exist yet which leaves the question: “Does the system really generate electricity?” 

The lack of a road test and real energy production numbers leaves an impression that Solar Roadways is more of a fun project as opposed to a problem solver. This does not mean that new ideas should be snuffed out or laughed at. What it means is that new ideas should have facts and figures in hand before they are pursued and funded with abandon.

If the $2 million raised on Indiegogo was used to purchase high-efficiency solar panels, then the energy generated from such a farm would be approximately 1.48 million watts, which could potentially provide power for up to 160 homes until the end of life of those panels. In fact, that money (along with the $750,000 grant from the government) could have been used to build a solar farm.

 

Summary

Unfortunately, when new and exciting ideas—such as self-filling water bottles and hyperloop transport—captivate the public imagination, logistics seem to fall by the wayside.

After considering the costs alone, solar roads are currently impractical. Instead of spending trillions on roads that may or may not work, proven solar farms could be built at a fraction of the cost and provide more (and real) power.

Regardless, research, funding, and support for these solar roads is likely to continue. Whether the movement finds a niche in parks and bike paths or expands into functional and permanent roadways will be partly determined by how much public interest it gets. But make no mistake—whether such projects succeed in their goal of efficiently harvesting solar energy is a question of engineering. At present, the odds don't look good.

 

Comments

21 Comments


  • Bryce Morrison 2017-04-21

    Although this post is dated one day ago (April 21st) on this site, it seems much older.  Some of the issues have already been addressed.  For instance, the webcam has been live again as of several months ago, when the nearby PC along with the public restroom became powered by the 15 panels in downtown Sandpoint.

    Point 1 regarding the angle of the sunlight had also been addressed, although I don’t recall whether it was from a public post, from a report on the Solar Roadways website (which is more likely), or from a personal conversation in downtown Sandpoint when I visited to attend the ribbon cutting ceremony.  The study had been conducted with panels flat on the ground versus panels angled towards the sun (south-facing).  Weather patterns and seasons were also recorded in the study, which found that angles didn’t make any noticeable difference.  In some cases, such as during the cloudy weather, I think I even saw the flat panel acquiring more power than the south-facing panel.

    For point 4, the accumulation of snow, I do wish the author would have observed the outdoor tests that had been done over the winter. Without any external source of heat, and even during the intense winter we had in the Inland Northwest, the SR2 model prevented any accumulation of snow.  It’s not meant to remove pre-existing snow, but to melt snow as it’s coming into contact.  In support of the sun-angling issue, these panels were located in front of the office’s entry door, which is on the northern side of their building (blocking direct exposure to the sun).  If you’d like to go back on the 2016-2017 timeline of the SR facebook page, you might see a picture of it.

    Thank you for sharing your insight on this sensitive topic, Robin.

    • ledsales 2017-04-23

      Problem 2 is also incorrect, standard common SMD LEDs (the most popular in OEM equipment), with packages such as 3528, 1206, 0805 etc, have beam angles of 120 degrees or greater, no optics required. Indeed, it’s the narrower angle LEDs that have optics, for example, common through-hole LEDs have optics built into the LED case to collimate the beam, LED chips by design have wide dispersion angles.

      If you want to reduce light emission straight up then you just fit two side emitting LEDs back to back, one facing each direction down the road, there’s nothing to it.

      However, I agree that overall, solar roadways make little sense, they are far more expensive and energy intensive than putting PVs on the millions of unused rooftops across suburbia, or making PV “canopies” over bike lanes and even roadways, which would use standard PV panels and simple framing. There are many places that PV panels can be mounted that are better options than in a road surface, indeed almost any other surface is a better option than in a road surface.

  • Vish Ram 2017-04-25

    Hi,

    I got some different solar road Concept, which solves 2 major issues of Solar Energy Early Implementation i.e. Land & Funds Issue,
    for complete details just check once in DETAILS

    http://lightenmyways.blogspot.com

    or

    search for Clean & Green Future !!!

  • p al 2017-05-05

    Previous posts supposedly addressing the well founded criticism in this article are mere wishful thinking. This is a pie-in-the-sky boondoggle idea. The money required for even a fraction of this wacko idea to work, would be better spent on the only real, proven and feasible renewable energy source….HYDROELECTRIC. (and perhaps also existing nuclear with more safeguards, and fusion with more research $$, that being diverted by these bonehead, fantasy ideas.)

  • Spark_36 2017-05-05

    One thing that came to mind reading the article and comments: These roads are supposed to be carrying cars and trucks ? If so, how will the sunlight reach the panel with a lot of cars either driving or standing on them ? Or maybe traffic jams are all ended with electric cars and solar roads ?
    I might be missing something here, if so, please enlighten me.
    The article is very good, but it should maybe have mentioned the total cost of solars….. mining the minerals, energy used processing the wafers (which is considerable), transportation of panels (shipping)..... which actually all in all gives no netto gain in reducing emissions.
    I totally agree p al .....wishful thinking and probably “invented” by people with very little experience in how to make things work in reality, and too much time on their hands.. But when asking for funding to a project, just mention CO2, and the world is at your feet.

    • Vish Ram 2017-05-08

      Hi,

      I got some different solar road Concept, which solves 2 major issues for Solar Energy Early Implementation i.e.

      Land &
      Funds Issue,

      Its “Solar ROOF on Roads With Rain Water Harvesting System & Advertisements”,

      for complete details just check once in DETAILS

      http://lightenmyways.blogspot.com

      or

      search for Clean & Green Future !!!

    • Doktor Jones 2017-05-15

      Solar roadways would be least feasible in congested places like Los Angeles… however, on freeways outside of cities, rural roads, and the like… there’s lots of sunlight falling on empty black asphalt. These are the places where solar roadways would have the most benefit because they spend 90% of the day baking in the sun with only periodic passing cars.

  • jrj90620 2017-05-05

    As long as there’s still plenty of roofs without solar,why not put these up first,before doing roads,which have so many problems?

    • Vish Ram 2017-05-08

      Its Because, Public is not too much aware of Benefits of Clean (Solar) Energy & also its investment return is taking too long, yet another way we can more efficiently use Roads by putting Solar ROOF on Roads, which solves 2 major issues for Solar Energy Early Implementation i.e.
      Land & Funds Issue,
      Its “Solar ROOF on Roads With Rain Water Harvesting System & Advertisements”,
      for complete details just check once in DETAILS

      http://lightenmyways.blogspot.com

      or

      search for Clean & Green Future !!!

  • grahamed 2017-05-05

    I look forward to driving on smooth, wet glass

    • Spark_36 2017-05-05

      lol ... spot on grahamed ! Add 1 cm of 0 degree snow and disaster is imminent.

    • mgksmoke 2017-05-05

      LOL. That was the 1st thing I thought about this concept. The whole concept has been thoroughly debunked.  11 years later were past the wishful thinking stage and headed towards scam territory.  Rationally engineered solar has it’s own issues. This boondoggle is damaging to legit solar applications.

  • cuyler1 2017-05-05

    I first read of solar in the ‘70s in an old book from the ‘60s. I built solar water heaters , then solar air heaters for my shed then home. then the ‘80s pased-the ‘90s,‘00 and into the 20teens. I live in Florida where nosnow below orlando and I wonder what even 1 mile of panels installed above/along the interstates power has been lost. Lost forever!

  • raconst 2017-05-05

    If the idea is to reduce CO2 emissions, imagine how much could be saved by NOT manufacturing these horrendously expensive gadgets.  And what is the coefficient of friction of glass?  And how quickly will the efficiency of these things diminish when coated in road grime and rubber?  Fantasy.  Now, roof tiles may just be the answer Mr Tesla.

  • jenden2005 2017-05-05

    This all sounds, well, crazy. Why try to get PV from roads? Make roofs of PV; use the power where its made, and not complicate it with 2000lb cars driving across it. Its not like we don’t have room for panels, its the cost of protecting those panels that gets in the way. This idea just makes that cost even worse.

    That said, a simple pipe network embedded in current asphalt would be a virtually unlimited supply of hot water for buildings alongside said roads .. and add much less engineering issues.

    Judicious use of embedded LEDs to create smart roads sounds promising though .. imagine a road that adapted to incoming morning traffic and exiting evening traffic by changing lane directions/quantities .. now that might make some sense. The optical angle is not that hard to solve; mount angle, simple reflective devices, whatever. Just put the LEDs into existing lane marking reflectors even.

    • Rick Glimmer 2017-05-06

      The answer is actually pretty simple. Roads are built and maintained by government, rooftops are owned by individuals and companies. Which would be easier to extract money from. A bunch of politicians or the rest of the population. Solar roadways is precisely targeted to government and non engineering people on indiegogo. You throw in a few sentences like ‘save 75% greenhouse gases’, ‘free enrgy from the sun’ and boom you have the support. Throw in a easy to understand but full with lies and unsubstantiated claims presentation and you win over a lot of those targeted people. You just say what they so desperately want to hear.

  • hgear 2017-05-07

    There are so many unmentioned problems too.  What about all the cars sitting on the roadway (especially during rush hour) or on a parking lot, shading most of the panels?  What about a car accident, which damages a large section of panels?  In terms of melting snow, you also have to remember that when it’s snowing, it’s necessarily cloudy, and there won’t be any solar energy being generated to melt the snow.  What about traction on the glossy, clear glass?  Roughening the glass for traction will seriously impede light transmission.  On and on with the neglected problems in the whole concept.  Solar farms are a far better solution - put in areas where sun shines, angled optimally towards the light, no obstructions, no damage from accidents, easier to replace, etc.  And, it has been shown that the area needed for enough solar farm panels to power the country is relatively small.  Let’s keep roadways as roadways, and solar farms as solar farms.  Attempting to mix the two is just bad engineering.

  • Vish Ram 2017-05-08

    What You all Say About putting Solar Panels as ROOF on Roads i.e. “Solar ROOF on Roads With Rain Water Harvesting System & Advertisements” ???

    It solves 2 major issues of Solar Energy “LAND” & “FUNDS”, & it also helps to Implement Solar energy around the World in Very Less & at the Same Time.
    Complete Project Details can be checked below,
    http://lightenmyways.blogspot.com
    or
    search for Clean & Green Future !!!

    • Doktor Jones 2017-05-15

      Really dude, we get it. You don’t need to copy/paste your post 3+ times in the same comments section.

  • freesoftDX 2017-05-08

    i’m sure that some of these issues can successfully be addressed, but there is still a good chance that it won’t be economically viable.  were the glass-covered solar panels to be replaced by nanomachines, however, things could be addressed differently.

    first of all, the nanomachine would need to use a molecule like chlorophyll for capturing energetic photons.  after that, or perhaps as part of that (i remember few of the details of chlorophyll’s energy capture and transmission), the energy would have to be converted to a minute current, perhaps using a charge pump of some sort.  the flagella of escherichia coli are driven by electrostatic motors, so i suspect that this charge pump could be borrowed from the biosphere as well.  the charge would then need to be sent onto a bus of some sort.

    this bus would have to be formed by the nanomachines connecting to one another.  my guess is that they would have to hand off charges coming into an intake “port” to an outgoing “port,” adding its own charges as well, and at some point, there would have to be either a different nanomachine, or a group of nanomachines working together, to act as a charge “sump.”  if this is large enough, it might be able to detect and connect to fine wires leading to a macro-sized port which could charge a battery.

    besides having charge-passing ports, the nanomachines would have to strong bonds to one another, because they would form the pavement.  since they would most likely be built from modified proteins or enzymes, the bonds forming the mechanical connections would probably be strong covalent bonds.  i can’t see such nanomachines being very cheap to produce, at least at first, and because only the top layers of the pavement would be able to capture photons, it would probably pay to make the pavement a two-phase material, with something like a high-tech concrete (or even asphalt) underneath the nano layer, with the two bonded together by slight mixing at the interface and the second material (fiberglass, perhaps?) bonding them together.

    some residential solar energy installations are all about generating hot water, not electricity, so to keep the pavement ice-free, it might be desirable to bury a network of small heat pipes in the pavement below the solar photon-capturing surface.  the heat transfer fluid would have to be environmentally friendly in case of line breaks, which pretty much requires that it be water with some relatively harmless chemicals in solution.  U can only take the temperature down so far with this, however, so it would also be necessary to embed heating wires (or something like that) in order to bring extremely low temperatures up to a level at which the heat pipes could take over.  even then, there are likely to be temperatures so low that ice forms anyway, but it would be really nice if *most* of the pavement could be kept clear most of the time.

    of course, all this is blue-sky until somebody actually tries it, which is why i’m throwing it out there.  as Solar Roadways and others have found, confirming the experience of innumerable governments, roads are expensive, even if built with the cheapest materials and badly maintained.  i can barely keep my own head above water, let alone providing millions for power-road prototypes!

  • mgksmoke 2017-06-23

    We’re YEARS past (5th grade back of the envelope calculations) stupid idea and into scam territory.