Solar Roadways - Working prototype and pictures!

[doug]

But a far, far better way of knowing what's on the road is by using a SmartSensor HD

Yeah, my only point was that this was already being done, for decades.

 

[c041v]

I look forward to this response, since I keep hearing arguments from both sides on this and unfortunately for my simple mind (at least simple minded on this subject) both sides seem to make sense to me... Which has made it all the more confusing since I don't know which side to believe now.

Background:

I am a University educated Civil Engineer that has worked on three major Highway Improvement Projects in Canada, all of which were over $500 million in value. I have been directly involved in Pavement design, roadway removal, reconstruction, rehabilitation and new construction.

Just wanted to get this out of the way first - Skid marks are not solely created by rubber tire. It is a combination of the rubber tire and the asphalt binder (oil) used to hold the aggregate together. When a non-rotating tire travels across the road surface, the heat generated melts a localized area of the asphalt below, bring some of the binder to the surface as well as sometimes leaving a rubber deposit, which is why you see an area that is typically darker than its surroundings.

I imagine that glass roadways would not suffer from this problem, or at least the only skid marks you would see would come from rubber deposits, and they would last for a much shorter period of time.

I took the time yesterday to read all of the responses watch all the videos and, read each FAQ on the Brusaw’s website. After having read a number of the responses so far, I think a couple of very good points have been brought up by a number of members. I do want to say that I really like that someone has taken the time and energy to develop this technology as I do see some limited applications for it.
That said, I believe these to be the key takeaways from everything that’s been said so far;

1. Parking lots & driveways are likely the only application that solar roadways will work for.
2. There is a lack of information concerning some of the design specifics, so I’ve made some assumptions in my responses.
3. I don’ know enough about electricity and how much is involved to heat a road, but I just cannot see it being worthwhile in rural or lightly used applications, especially in the great white north where you could be heating a road for up to 4 months in sustained subzero temperatures, so I’m not going to touch on the heating aspect. That Australian fellow ran a lot of numbers on the power generations aspect anyways, so I’ll stick to roadway engineering.

In no particular order, here are my thoughts;

Adjacent trenches for Drainage/Componentry

These look pretty nifty in the video, but in reality, trying to incorporate this into an existing road would be an absolute nightmare. We normally cut ditches for;

a) Room to recover if you leave the road and
b) Because it’s the cheapest form of drainage
c) There is some Road design formulas concerning the amount of open space you need to have in order to feel comfortable driving at X speed.

Installing a concrete trench for drainage along the side of a road is extremely expensive. We had to do this for a 2 kilometer section of the last project I was on as the existing highway we were matching to was too wide. We basically would have been promoting sheet flow to the outer lanes by linking the two roads together so we needed to put a trench in the middle of what were ultimately 6 lanes of existing/new road. This was by far the most expensive drainage system that I have ever been involved with, and it could only be done at night due to the area required for the machines to work. Any way you cut it; this was something that nobody I’ve worked with has any desire to ever do again.

Additionally, we built a drainage reservoir that was about twice the size of the duct that the Brusaw’s show in the video. We’ve actually done a lot of these, in both Precast and Cast-in-place (CIP) concrete. Precast is infinitely faster, but does require significant grading and larger equipment to handle the sections. It is an extremely rare application to run any sort of channel parallel with the roadway given the cost and difficulty associated with constructing it.
On the flip side, running conduit lines along a road is a much easier thing to do. If they could somehow make it would with conduit and junction boxes, this makes things quite a bit easier in terms of constructability. You could even upgrade this to a something in the neighborhood of a water or storm main (600 – 1200 mm pipe) that would potentially allow for some access, but it would still be an expensive proposition.

Settlement

Roads are heavy! I’ve carved highways into mountains, across peat bogs and on plain old sedimentary soils over bedrock. As AudubonB mentioned, the subgrade strength comes into play when designing a road and accounting for what it will eventually do, especially in extreme weather conditions. Roads in areas of compressible soils or weak subgrades will settle under their own weight over time, which is why rehabilitation is such a practical solution where differential settlement inevitably occurs.

This is aside from any temperature factors that I do believe will play a much larger role than what the Brusaw’s have indicated in their FAQ. I can only guess what happens when you have a warm chunk of land in between two frozen ones that are much larger. It may not freeze locally, but I think it’s folly to assume the road is immune to global lateral/heaving forces.

As someone else pointed out, the earth is constantly moving. Rigid roads do exist, but not really in Canada, partly because of our huge temperature differentials. However, there may be some environments where the geography is seismically and climate stable enough that these effects would be minimized (South states). You can get around compressible soils by applying the cubic dollars principle. Good luck with tidal zones, where you have a constantly varying groundwater table that is sensitive to not only daily events, but fluctuating seasonal changes as well. Those areas are also not some place I’d want to install a channel full of electrical wiring.

Materials and Production

I can’t imagine trying to introduce a new product that may have an extremely slow installation rate on any sort of major roadway. Our paving crews needed to put done at least 1 lane kilometer of road to be profitable each day and they had the benefit of a reasonably close aggregate supply that could primarily barged within a few kilometers. Trucking costs can easily account for the majority of a material’s placed cost. I would think that even recycled glass would be an inconsistent supply at best, and it would need to be sourced from Recycling facilities.

I have no idea where the cost figure of $10,000 for a 12’ x 12’ square came from or what it includes. I can tell you the material cost of a standard 4 lane highway is probably an order of magnitude less, even with multiple rehabilitations factored in. Some of the indirect factors like design and management are unavoidable whether you are building a solar or asphalt road. There are also some life cycle savings that come into play when roads are milled and old asphalt and/or gravel is recycled.

Further, I am curious as to how they intend on incorporating their product into an existing roadway. The material requirements for new road construction are staggering. My last project saw some 400,000 MT of asphalt and 2,500,000 MT of gravel for ~ 40 km of 4 lane highway. All pavement design is done with an eye to locally available materials. Everything we used came from local quarries and was transported in the largest possible devices we would economically use, i.e. 4,000 Mt barges. I don’t know what the Bursaw’s envision in terms of production equipment, but I’d wager it will be very slow and of limited capacity, meaning that the road will take a long time to complete.

I am not able to tell from the existing literature on solar roadways if they intend to build new roads, or modify existing. Either way, you are bound to run into a Traffic Management or Material procurement issue. Even if they could entirely eliminate the asphalt material component (Not likely due to the structural integrity it provides to an overall road structure) you need to source a massive amount of glass, metal and all of the other components that go into producing each hexagon.

Braking Forces

I’ve consulted a few studies and I believe the concept of Shear Spring Compliance is something that has not been considered in the initial trial so far. This is basically the measure of the bonding between asphalt layers. Think of it in terms of plywood, where you have several layers of wood bonded together to create and end product. It you apply enough friction force to the top layer, while keeping the lower layers relatively fixed, it will slip from the bond. The same principle applies to asphalt.

There is a practical limit to asphalt layer thickness, which is part of the reason why most major roads are made up of several layers of asphalt anywhere from 40-125 mm in thickness. These layers are often bonded with a product known in the industry as “Tackifier” or “Prime”. It is a hydrocarbon emulsion that is blended with water for application, that chemical evaporates to leave a glue like residue that bonds asphalt layers together, and also prevents (to a degree) capillary action from water in the gravel layers below to resist cracking.

This slippage between asphalt layers is most noticeable in areas where trucks accelerate or decelerate. Hills are the worst, are they are travelling at low speed and constantly changing gears, which create uneven friction spikes as axle torque is constantly adjusted to allow the truck to perform the desired changes in motion. Highly experienced road builders can actually point out where trucks change gear on a hill based on the ribboning you can see in the asphalt profile where the layer has slipped.

My concern in terms of solar roads are that they may have the necessary hardness, and compression strength, but the hexagon panels are not likely to be able to resist these tremendous lateral forces particularly well. I’m mostly concerned since each panel is only bonded to the next by a generic “mastic”. The advantage, as highlighted by in some of the FAQ, is that each panel may be individually serviced or replaced. A disadvantage is that the road surface does not possess any sort of uniform strength in resisting lateral forces. The contact patch of any tire is small enough to fit on one of these panels, and I would be very curious to see how well it held in place over time as a fully loaded truck is changing gear going up a hill. I’m thinking that the hexagons will act like a macro version of cobblestone in that they will all end up doing their own thing over time.

I understand they are positioned in some sort of grid, but I am somewhat skeptical about their ability to remain in place after years of lateral friction trying to shift them around. You’d have to cast a concrete pad underneath to keep them in place, which would cost even more money.
Alternatively, if you were to cut them into existing asphalt, you’d need to somehow replace the strength of the layer you just removed. I can’t see the hexagons adding any additional strength as they don’t act as a structurally cohesive layer. I’m not an expert on layer strengths, but I can tell we couldn’t get our engineers to assign a structural value to a top lift mix that had a high air void content (20+%) that was still a designed asphalt mix, so I could not see something held together by mere mastic getting anywhere near a structural value.

Rutting resistance

In a similar vein to the above point, cars/trucks travel in fairly set wheel paths defined by a proximity level of comfort to the lane markings. As most people drive within the lanes, you’ll notice defined rutting as only a portion of the pavement takes nearly all of the abuse.
I am curious to see how they intend to design for this. Ruts are a fairly common occurrence on most major roads, and often most notable at intersections where a combination of the aforementioned lateral forces combine with the defined travel lanes to amplify stresses.

Cleaning

It’s nice that we won’t need snowplows anymore, but vehicles are still extremely dirty. I’m not sure if any dirt or other matter will have an effect on the output of the solar cells if it reduces the transparency of the glass.
There’s also the matter of oil/other fluid leaks from ICE’s that can sometime be very difficult to remove. Luckily these are usually relegated to the travel paths I mentioned above, but it is a concern nonetheless.

Traffic Management

To give you an idea of how big of an issue this is, we spent tens of millions of dollars designing, implementing, and maintaining detours on each of the projects I’ve worked on. It is one of these largest contributors to a project’s construction schedule and when it comes down to it, there are some very rigid requirements we must adhere to when shifting traffic patterns.

You simply cannot close a lane on an active highway without having a suitable alternative designed. This may involve the construction of a new road, modification to an existing shoulder or a dozen other things. My point here is that you cannot touch any existing road for any sort of rehabilitation or new construction without having to spend a serious amount of money to accommodate the existing traffic. The travelling public is also not terribly appreciative of the effort we go to improve their commute in the long run. Material cost of road construction is arguably the same in terms of overall project percentage as the traffic management process. We had nearly 100 engineered detours for one 12 km section of existing (albeit, major) highway in order to go from the existing configuration to the new design.

Asphalt is a unique and wonderful material in this regards that it can be used to fill very odd shapes and elevations to get traffic reconfigured. I cannot envision any other way in which road construction could occur without the usage of granular materials that can be placed either by the kilogram or ton. You never know what you’re going to need until you actually out there building it.

Summary

I don’t mean to sound negative, as I mention in the beginning, there are certainly some applications, like parking lots and low traffic areas where the end user will not be disrupted. It would also be much easier to connect the componentry to some localized control point rather than running a continuous trench/duct. The dynamic forces would also be greatly reduced as the speeds would be significantly lower.
I’d like to see them start with those applications rather than going for roads/highways.

 

[wart]

Kudos to you, c041v! That's the kind of analysis we needed.

I think it's possible we'll see solar paving tiles like this at something like an amusement park where they will only see pedestrian and light vehicle (i.e. golf cart) traffic, and the "gee whiz" factor might be valuable enough to justify the cost. Even at a parking lot I'd be concerned about the effects of occasional heavy delivery trucks. I'm pretty certain at this point that we will never see solar interstate highways.

 

[AudubonB]

Thank you c041v for re-injecting a badly-needed dose of reality into this discussion.

 

[dsm363]

I'm always amazed at the depth and level of knowledge so many have here. Thank you c041v for such an excellent analysis.

 

[chickensevil]

I learned some new things about how roads are built and the forces that destroy the roads and such, so very informative piece, thank you!

To answer your question about if they would build on new or existing infrastructure. Their website mentions that they can start with the available foundation and then build up from there. Depending on how good or bad that foundation is, as to how much work would need to be done. It looks to me from their pictures and such, that they are built on top of concrete. If I am not mistaken isn't that what the base layers are of the roads already? So seems to me like all they would actually be replacing is the asphalt on top... which doesn't seem like the most expensive piece.

Anyway, thank you for your insights, everything you posted makes sense as to why it would not be feasible for major roadways.

 

[c041v]

Chickensevil - I have an answer to your post, but will submit it tomorrow after I quickly spend some time with my secret love, Trimble's (formerly Google) Sketchup to properly illustrate the constituents of a road structure, as I have some renderings from an old job and nothing I could find really details it as well as I can. It varies a great deal regionally and does not typically contain concrete, at least in Canada. Much different story in the US and International situations, again dependant on local material supplies.


I've also thought of a couple more things, and will add them too.


edit: New info below.


Definitions:


CGSB: Course Grade Select Base (75 mm and smaller aggregate with a bias towards bigger bits of rock)
WGBC: Well Graded Base Course (25 mm and smaller aggregate with no bias towards the smallest bits of rock)
HMAC: Hot Mix Asphalt Course (Two types, the upper course has a slightly smaller aggregate size (19 mm) to increase the tightness of compaction as it it he material vehicles will travel on)

There's probably at least a dozen other types of aggregate layers and sizes that can be used, but I am only really familiar with Western Canada. Floridians should look closely at your parking lots and roads, sea shells are often used as as a supplementary aggregate In HMAC courses. That is but one example of how creative some markets get in hunting for suitable building materials. I know recycled glass is available in a lot of places, but I really don't know about the quality, consistency, supply levels, or proximity in terms of solar panels applications.

The attached picture is a typical section of the most recent highway I built in Vancouver. The asphalt structure is only 150 mm, Base course 150 mm, Sub-base variable at 385 mm and the sand sub grade was anywhere between 1000 - 2500 mm. The cross section is typical for BC in that we have access to a LOT of gravel. In Alberta and the Prairie Provinces, it would be more common to see the HMAC around 250-300 mm and little, if any gravel as they simply don't have geology. It is cheaper to add more asphalt (which is stronger) than try to find and quarry gravel. BC uses gravel as it is cheaper and does provide some structural support/cohesiveness that sand doesn't.


We we also have some sedimentary clays, but the issue with clays is that they don 't drain very well although they are extremely strong. Some clays work very well for sub grade layers. The sand sub grade I have illustrated is an embanked layer in that we built it above the existing ground (which was a cranberry field) composed of weaker saturated soils and peaty type organics. There's a bit more to it than that, but it gives you the basics.


Where I see a lot of difficulty in placing solar panels is that each of these layers are optimized for strength and cost. We actually fine tuned them a little more than what I've shown, but my point is you certainly can't eliminate anything without compromising the strength. You could place them atop this structure, but you're not exactly eliminating any road or saving any money. This is basically a budget version of what it takes to build a highway.


I also indicated the the lanes as they would be paved, as one must keep in mind the machines that build highways are sized to do it as efficiently as possible and for many kilometres. It is very slow and expensive to pave anything <5m wide, so we don't often do it.


Noise


Others have wondered about what a bunch of these panels strung together might sound like at highway speed. I don't know what it would be for sure, but I would think it would be similar to cobblestones or relief textured concrete. Roads do have unique noise signatures depending on the surface treatment. Concrete roads have a raked finish (to provide traction, parkades have a polished finish) and there are actually some types of asphalts that have anechoic properties due to their increased air voids. Any sort of raised texture is likely to produce a unique signature.


Drainage


I put the jersey barriers on my illustration below as they are an important part of how roads drain. It is rare to see more than a couple of lanes at a time angled in any one direction due to the problems encountered with sheet flow during heavy rain events. By draining the entire road in one direction, you can run the risk of ponding, thus creating a risk of hydro planing if the cross fall is not steep enough. In addition to keeping in attentive motorists on their side of hype highway, barriers help to Chanel water to catch basins, located in the centre of the road.


How does this affect solar roadways you might ask? Over time all the stuff that the rain picks up collects along the barriers. It's mostly dirt, which you can easily notice the next time you're out driving. Maintenance crews rarely remove it as it isn't a safety hazard, and it would take a lot of dirt to actually stop the drainage that is still occurring. This results in a dirty median that would likely severely compromise the transparency were a solar panel to be placed below.


Again, I think these panels would be great for driveways, where people tend to take more care of hype cleanliness, in addition to driving lighter vehicles at low speeds. Parking lots would also work, but roofs are just so much less work.

Lastly, to answer your question chickensevil - There exists something called a Cementious Base Course, or Cement Treated Aggregate that would be about the closest thing to the underlying road already being concrete. It is a process that utilized unreacted (non hydrated) cement mixed with aggregates to ultimately produce a much stronger sub base layer. It is used in areas where a stronger sub base layer is desired, usually for higher loads or a longer service life. I would also imagine it is fairly impermeable unlike the gravel layers I have illustrated.

To a degree, capillary action from water below can penetrate untreated HMAC layers causing them to slowly break up from below in environments where freeze/thaw cycles are present. We get around this by applying tackifier between the WGBC and HMAC layers. It is also applied between HMAC layers and greatly aids to reduce the aforementioned slippage between HMAC layers generated by heavy braking and acceleration forces. For those who are curious, it is generally either an emulsified hydrocarbon cut with water that evaporates over time to leave an extremely sticky tar, a chemically activated hydrocarbon that releases moisture when temperatures are too low for evaporation to occur.

 

[Mookuh]

Thank you for the very informative responses, c041v! There's a lot more to roads than meets the eye it seems

It might be worth installing Solar Roadways (or walkways) in places where you want the reconfigurable LED interface for show etc., but I don't think it would be a good idea to put them into parking lots (at least not under the actual parking spaces), because then you're putting solar panels in a space that is meant to have something cover it for extended periods of time.

 

[Robert.Boston]

Leave it to the Dutch to leapfrog the Americans on this issue. Interesting to see that it's going on a bicycle path first, rather than a motorway. That addresses a lot of issues with wear.
Renewable Energy: Dutch install world's first solar bike path

 

[AnOutsider]

Leave it to the Dutch to leapfrog the Americans on this issue. Interesting to see that it's going on a bicycle path first, rather than a motorway. That addresses a lot of issues with wear.
Renewable Energy: Dutch install world's first solar bike path

Solar Roadways response: But we've been SO busy filming thank you videos we haven't had a chance to work on the product yet!

 

[derekt75]

Leave it to the Dutch to leapfrog the Americans on this issue. Interesting to see that it's going on a bicycle path first, rather than a motorway. That addresses a lot of issues with wear.
Renewable Energy: Dutch install world's first solar bike path

Did that quote say $3.7 million for 70 yards of bike path that will last 3 years? Am I misreading something?

70 yards of bike path should cost more like $1k.
Generating 10,000 kWh per year (70 kWh/yr/yd² * 2 yards wide * 70 yards long) in California would cost under $20k. Netherlands gets less sun, so maybe $50k there?

So $1k + $50k = $3700k? Surely I'm misunderstanding something?


I'm amused that this is being done in a northern country where it rains about once every two days. I suppose it could have been Edinburgh or Prudhoe Bay or something, but the number of cities that get less sun is not large.

 

[liuping]

Did that quote say $3.7 million for 70 yards of bike path that will last 3 years? Am I misreading something?

The test is 3 years. I would think the path should last longer.

At $3.7 million for 70 yards, their 35km of bike paths would only cost $2.023 trillion. :scared:

 

[doug]

The cost just illustrates what a poor idea this is. There are smarter places to install PVs.

 

[basvk]

I guess the development cost are part of that 3 million euros, it's probably not the price of just that 70 meter stretch. I agree that there are probably more efficient ways to harvest electricity from sunlight than this...

 

[HVM]

Time to kill this thread also..

 

[wk057]

Time to kill this thread also..

Yeah, I'm pretty sure this solar roadways nonsense has been thoroughly debunked....

 

[Zextraterrestrial]

More BS

 

[doug]

Turns Out A Road Made Of Solar Panels Was, In Fact, A Bad Idea - Jalopnik

Obviously bad idea is bad.

The French newspaper Le Monde reported that, after two and a half years, some things have gone wrong:

• The road had to be shortened by 100 meters because a portion was too damaged to be repairs
• The protective resin is peeling off the portion that remains
• Leaves and trees fall onto the panels and, you know, block the sunlight
• The noise from cars and trucks driving over the panels is so loud the speed limit had to be reduced to about 45 miles per hour
• It is generating less than half of the electricity expected because the panels could not be angled directly at the sun and Normandy isn’t exactly known for its year-round sunshine

 

[nwdiver]

Turns Out A Road Made Of Solar Panels Was, In Fact, A Bad Idea - Jalopnik

Obviously bad idea is bad.

*Sigh*

Well... at least we still have our Hydrogen cars.... right?