Solar freakin' roadways? Why the future of this technology may not be so bright | RenewEconomy

Solar freakin’ roadways? Why the future of this technology may not be so bright

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When we are not driving, cycling, or walking on it, a road is just a waste of space, right? Not if it is a solar road!

Might the sun set on this technology before it’s even taken off? [email protected]/flickr, CC BY-SA
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The Conversation

Might the sun set on this technology before it’s even taken off? 129664508@N08/flickr, CC BY-SA
Might the sun set on this technology before it’s even taken off? [email protected]/flickr, CC BY-SA

When we are not driving, cycling, or walking on it, a road is just a waste of space, right? Not if it is a solar road!

What a perfect combination. When it’s exposed to the sun, the road is generating clean electricity, mitigating our production of CO₂, and hence our impact on global warming.

The American Solar “freakin” Roadways is an internet phenomenon raising over US$2 million in crowd funding. They have an attractive marketing campaign and make compelling arguments for their technology. Also, the Dutch SolaRoad project has produced a 100m cycleway pilot project, which demonstrates the technical feasibility for light traffic.

Solar FREAKIN’ Roadways!

Are we seeing a tipping point where the explosion in solar growth is now going to be cross-pollinated to parts of our road networks? Not likely with the concepts above.

These projects are based on PV modules made of cells and a cover glass about a centimetre thick. Without a complete technological change, it will remain a niche industry without significant impact.

Reason 1: Price

Per square metre, bitumen/asphalt roads are cheaper (around $5/m²) than centimetre thick slabs of toughened glass (around $15-20/m²), and this will not change. Asphalt is a mixture of waste products from the refining of oil, and fine gravel or aggregate. Glass, on the other hand, is formed by melting silica, and is energy intensive to produce.

Perhaps recycled glass could be used instead of refining new silica, but with a big performance hit. A centimetre of solar glass will transmit 91% of usable light; typical recycled glass will transmit only 35% (you can perform this calculation here, by comparing transmission of a centimetre thick glass substrate of green sodalime and low-fe glass).

The energy requirement of making thick solar glass is far higher than that of the glass used in standard rooftop PV. So, no matter the innovation, it will be considerably more expensive than the status quo. Does the energy generated form a solar road make up for this cost, not when you compare it to building a road and installing rooftop PV separately.

Reason 2: Performance

Roads are not orientated to face the sun. At best this is a 20% loss from traditional rooftop PV installations (see the Desert Knowledge Solar’s solar clock’s yearly performance, comparing the flat orientated system 16b to the north orientated system 16a), but it could far higher.

For example, most roads are at ground level and are easily shaded, meaning they cannot take advantage of most of the sun’s usable energy (i.e. direct sunlight). And as roads are prone to collecting dirt, this would further shade the modules.

PV panels work best when they are cool; this is why their backing is typically exposed for ventilation. It is likely that solar roads would operate at higher temperatures, further reducing their performance.

Simply put, a solar panel on a roof will perform far better than a solar road.

Reason 3: Safety

Imagine driving on a smooth glass surface, in the rain.

Road surfaces wear with use. As asphalt roads wear, layers of the fine gravel are removed, exposing further layers of rough gravel/aggregate, maintaining the surface consistency and grip.

Conversely, glass is a malleable network of homogenous material. Hence over time it wears smooth. Because of these material properties, even if the glass road surface were given a textured pattern to provide traction, it would eventually be worn away.

For real applications, where vehicles are driving over it in all weather conditions, solar roads with glass covers will not provide sufficient traction to ensure the safety of its users.

Why we need to rethink this technology

Reasons 1 and 3 are deal breakers. The key requirement of a road is that it safely and cost-effectively provides a pathway for vehicles to transport the people and materials we need to run the economy and our everyday lives. Reason 2 is important as the perceived benefit of these roads is often overstated. Sure, solar is very cost effective when compared with conventional generation in many parts of the world.

Where solar is cost effective, it is: well set up (orientation, shading, ventilation, and so on), not required to be a structural element (hence a standard module is sufficient), not displacing economic assets, and there is an electricity demand it can directly supplement.

These conditions are often well met by rooftop solar systems and small scale solar farms, they are not well met by most roadways. For solar roadways to be effective, it needs a complete technological rethink. A solution may exist, but it probably isn’t solar electric. Perhaps solar chemical reactions will come to the rescue, inspired, for example, by air cleaning pavements. For now, a road that is covered by a roof that supports solar panels, or perhaps roads that are simply lined with solar panels could suffice.

Of course, it is important to explore all alternatives for green electricity generation. But let’s not allow our excitement for a technology that appears far from viable on a large scale detract from the fact that rooftop PV is fast becoming the cheapest method of generating electricity.


Source: The Conversation. Reproduced with permission.

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  1. Miles Harding 5 years ago

    There’s no need to get steamed up about this.
    Simply let the promoters go wild, but don’t use superannuation or public funds for it.

  2. Albert Sjoberg. 5 years ago

    Oh what a load of codswallop.
    1. Price – initial costings will always be high. The roadway offers several advantages that are not considered in the simple first blush glass costs more than asphalt argument. Costs like running overhead cables, where the Solar roadway includes trunking channels that can carry power and communications. Cost of maintenance and ice/snow removal also stacks up here. Costs will come down over time.
    2. Performance – This is known and addressed. less production is still more production than a road surface with no panel…
    3. Safety – addressed in the very first prototype. The surface is textured. The texturing provides good traction and drainage. The cost of laying salt and removing snow is not insignificant. A heated roadway surface is a safer surface. The possibility of warning motorists about hazard ahead is also a major safety factor in favour of Solar Roadways.

    So not deal breakers, but considerations the manufacturers/designers have already addressed. Unlike the lack of thought that apparently went into writing this article, the proponents of solar roadways have never advocated their product to the exclusion other uses of solar, but rather to augment the other uses.

    • john 5 years ago

      This is not exactly a good idea honestly
      There are far more simpler and cheaper places to place PV not in a road this honestly a dumb idea

    • Pedro 5 years ago

      Point 3 is the real application of this product. Micro power to warning devices set in the road and you may only need a couple of road pv panels every 10 meters or so.

  3. Jo 5 years ago

    I am grateful to see a critical comment on this technology. There is a danger in doing things that deviate from the main path of solar PV. If there are principle deal breakers we should rather use our ingenuity and resources on better options.
    This is true for PV roads, for artificial trees and for lots of other fancy ideas that appear in this context from time to time.

  4. Peter Campbell 5 years ago

    Build a solar roof over every large unshaded car parking area using light-weight solar panels, unconstrained by any need to double as an adequate road surface.

  5. Jacob 5 years ago

    It never passed the common sense test.

    Roads are so dirty and often unpainted.

  6. john 5 years ago

    A total dumb idea
    In car parks cover them in PV and the result will be far more output
    This is a totally not a good well thought out idea.
    Frankly deluded and not going to fly end of story

  7. Albert Sjoberg. 5 years ago

    “Never interrupt someone doing something you said couldn’t be done” Amelia Earhart. I am fascinated that so many people appear to be anti innovation.
    Yes, it is a radical idea. And yes it may never amount to anything. But it might just work or It may simply be a stepping stone to another technology.
    If you have not invested in his idea, then you certainly do not really have a stake in the game.
    I have no problem with giving Solar roadways the space and time to prove or disprove themselves. There are certainly worse ways to spend money.

  8. ROBwithaB 5 years ago

    Old story.
    Debunked months ago.

  9. Ian 5 years ago

    There is a concept we can salvage from this mad idea. Dual purposing of land use. Both road and solar plant . As others have said, put a roof over a road or cyclepath, or car park and cover this with solar. Shading and solar . Railway lines would be very suitable for this purpose: transportation, energy production. Rainwater capture could be added: transportation, energy and water. Roads could be used for solar heating . Heat capture, and storage for district heating , plus transportation .

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