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Wattway: A Photovoltaic Road

20 March 2017

Solar road. Credit EFESolar road. Credit EFEA year ago, France's Ecology and Energy Minister Ségolène Royal announced that within five years it was planning to pave 1,000 kilometers of roads across the country with solar cells. Well, this week the project was inaugurated with its first kilometer "paved" with photovoltaic panels. This first kilometer of road premiered in Normandy and is covered by 2,800 square meters of solar panels, which are able to generate the necessary energy for the operation of the public lighting system of the town of Tourouvre-au-Perche, with 3,400 inhabitants.

The idea behind this project by the French government is to be able to promote sustainable energy and use this technology to supply power to homes or public infrastructure systems, especially in those sectors where distribution is more difficult. Making the project viable is the fact that between 10 and 20 percent of the time the roads are covered by the transit vehicles while the rest of the day time the surface is open to solar energy. In addition, the roads provide an opportunity to take advantage of the solar energy without having to invade the agricultural surface or to modify the natural landscapes.The panels can withstand heavy vehicles. Credit: ColasThe panels can withstand heavy vehicles. Credit: Colas

This technology is the product of five years of research by the company Colas, subsidiary of Bouygues, in collaboration with the French National Institute of Solar Energy (INES). Colas manufactures the panels that form the—what they call—Wattway, a term that implies the road’s capabilities to produce electricity. The panels are very thin (a few millimeters thick) and can be installed on top of any road surface without any additional civil engineering work, and can withstand all types of vehicular traffic. Every 20 square meters of panels can supply power to one house (not including heating).

“Today, our Wattway process is unique on a global level. The Solar Road will play a part in the energy transition and is a building block for smart cities,” said Colas chairman and CEO Hervé Le Bouc. This technology can be construed as a next technological step for the roads of the future.

“The roads of the future will be intelligent and able to communicate thanks to widespread development in sensors making it possible to provide real-time information on traffic, to manage traffic dynamically and to roll out automatic diagnosing programs in the pavement itself. One can also imagine electric vehicles being charged via induction technology,” adds Le Bouc.

Solar road in Normandy. Credit: COLAS-Yves SoulabailleSolar road in Normandy. Credit: COLAS-Yves SoulabailleThis first project, however, should be taken with a grain of salt. At present, the great disadvantage of this technology is its high cost, something that manufacturers intend to change over time, as their production increases and their use becomes more massive.

“This is a prototype that still has to answer several questions: its cost over time, its production and its lifetime given its conditions of use," said Jean-Louis Bal, president of the Union of Renewable Energies of France. “At the moment, with this technology, producing one watt costs 17 euros while photovoltaic plants on the ground manage to reduce the cost to about one euro per watt. It's still early, we're waiting to see how it evolves."

However, the great advantage of this technology is that the electricity produced can be connected directly to points of local consumption, such as traffic lights on the road where they are installed, or can even be connected to a distribution network or storage energy. In any case, the first step of this ambitious project is already taken. The first kilometer of road built will benefit 3,400 people with self-sustaining energy. It now only remains to be seen what can be achieved with the next 999 km to be built. Depending on that outcome, perhaps this initiative is an alternative worth emulating in several countries.

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Discussion – 2 comments

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Re: Wattway: A Photovoltaic Road
2017-Mar-25 1:43 PM

I have always talked about how it would be marvelous if someone could design a way to efficiently accomplish this.

Another idea I have always had and, something that could be run even from this photo-voltaic grid is a series of wires similar to those used in the rear windows of automobiles to defrost the rear window. I have always felt that if a grid like that were to be installed in the construction of the highways that it could be used for the purpose of melting off the ice and snow as it happened in areas where that is a problem thus cutting reducing or possibly eliminating the use of snow plowing equipment and corrosive salt on the highways.

Of course there would then be a need to come up with a way to run the water from off of the highway so that it would not become a problem.

This is an excellent start though and one that I would like to see more of in the future.

Re: Wattway: A Photovoltaic Road
2017-Mar-30 3:08 PM

@DarrylS I have always talked about how it would be marvelous if someone could design a way to efficiently accomplish this. ...

It has already been done, and this is NOT it!

To efficiently use expensive solar panels, you want them oriented to the sun, and never covered by shade. And you certainly don't want to drive vehicles over them! Everything about these "Solar Road" approaches are backwards - it adds expense and reduces efficiency and creates reliability problems for no reason. Triple-lose.

Simply mount large installations of solar panels on the flat roofs of commercial sized buildings. Mount them at the optimal angle, which you can't do with a flat road. They won't have the sun blocked by cars driving over them, they won't need to withstand the weight and wear of traffic.

@DarrylS This is an excellent start though...

No! It should end here! This is the wrong way to do solar! Anyone who wants to see more solar should plead to end these silly things, it gives solar a bad name.

@DarrylS ... a series of wires similar to those used in the rear windows of automobiles to defrost the rear window. ... it could be used for the purpose of melting off the ice and snow ... cutting reducing or possibly eliminating the use of snow plowing equipment and corrosive salt on the highways.

Actually, that is sometimes used for limited areas like sidewalks or drives approaching a building entrance, where keeping it clear is more important than cost. And it has been experimented with for some short stretches of steep, icy roads (some place in WA state IIRC). But it takes vast amounts of electrical power to melt even an inch of snow, and those panels won't be producing power during a snowstorm. Plowing is much cheaper, probably more effective, outside of maybe a few niche application. Try doing the math on taking 4" of snow (roughly 2~4 # per sq foot), on a mile of 2 lane highway through its melting point, which takes ~ 144 BTU per pound, or 42 watt-hours. And factor in large heat losses (it's not like you can insulate that snow as you melt it). Well, let's see (assuming zero heat loss):

24' wide * 5280 feet = 126,720 sq feet

times 3#/sq foot = 380,160 # of snow

times 42 watt hours to melt it , which is ~ 16 Mega-Watt-Hours. Before considering losses. For reference, a mid sized home in the US uses ~ 1 MWHr for an entire month.

A snowplow would probably use less than a gallon of gas for those 2 miles of roadway - and that is ~ 32 kWh. For easy math, assume half the energy is lost in heating the snow to melt it (probably much more), that makes the snowplow 1000x more efficient! And that assumes you could have 16 Mega-Watts available, per mile, during a snowstorm!

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