The sun's rays can hit some roads for up to 90 percent of the daylight hours, so companies in Europe and the U.S. are experimenting with building solar panels along or above roads. But are such projects worth the cost? In France one company is hoping to distinguish itself—and reduce costs—with solar panels that are laid directly on the pavement
There is a project in the United States called Solar Roadways, which consist of concrete slabs including the solar cells plus tampered glass on top of it. There's a quite similar project in the Netherlands called SolaRoad. A section on a cycle pass was built about one year ago but it's large concrete slabs, which mean that in fact you're completely rebuilding a road. Our technology is different in that way that in fact we just placed our solar panels on an existing pavement; it does not require all that amount of preliminary works.
The first idea was generated about ten years ago and it came from the feeling that in fact the road looks of the sky for more that ninety per cent of the time. So during that ninety per cent of time it can collect energy from the sun.
We had very good opportunity to work together with the people at the national institute of solar energy. Their knowledge is photovoltaic technology, our knowledge is how to build roads, and we worked together to find the solution to the several problems we had to face to be able to integrate this technology on top of an existing pavement.
We had pages and pages of questions, what will be the grip on such a surface, which type of material should we use, which ratio between the active solar surface and the road surface, how can we maintain it, how could we recycle, and so on.
We tested several mixes of resins, of glass beads, of broken glass and so on, until we find a good compromise between the grip level and the light absorption.
These solar panels will produce electrical energy and the use will be quite similar to the one you could have with traditional PV panels placed on rooftops. You can either connect them to the global electricity network and in that case you're re-injecting electricity into the network or in case of more isolated locations, you can simply store the electricity in batteries and then use it for example public lightning, or you could even also imagine in a longer term that you could also supply electricity to electrical vehicles, for example either through traditional plugs, or even trough wireless technology such as induction.
The concept of solar road try to face two major problems of development of solar energy. The first problem is the lack of surface to produce enough energy, and the second problem is a problem of cost of the systems.
And when you use a solar road of course you take advantage of large surface of existing roads, so most of the work has been done, and you just have to integrate your component on a road.
I can see two problems with solar roads. The first one comes from the heating of the solar panels, because when the temperature of the panels increases, the efficiency decreases, and the aging process are accelerated.
And the second one is that for the prediction of the solar energy production you will have to integrate the traffic road modeling to be able to predict accurately the electricity production.
Another interesting parameter to look at is the energy payback time, which is the time necessary to produce the same energy that has been use to produce the panels. So it's a real challenge for engineers.