France's Solar Roads Plan a Costly, Inefficient Boondoggle

Joel Anderson  |

And lo, the idea that wouldn’t die raises its head once again. That’s right: Solar roads, the impractical concept that has nonetheless captured the imaginations of many well-meaning Indiegogo users and even the Dutch government, is back...again.

This time, it’s France. The French government has revealed plans to install some 1,000 km, over 600 miles, of solar roads using the Wattway system, technology developed by international roading company Colas. This is, by far, the most practical and realistic stab at the concept thus far. However, the evidence seems to suggest that this is a massively expensive boondoggle, putting government funds into an inefficient and expensive form of solar power, despite readily available options that are clearly and obviously superior.

A Road in the Right Direction?

So, for starters, it really should be emphasized just how significant an upgrade this is over the ridiculous plans from the Brusaws of Idaho. Wattway is a thin layer of photovoltaic cells, treated with a protective coating, that can simply be rolled out over existing roads. Rather than a suggestion for ripping up trillions of dollars worth of infrastructure, Wattway is designed to work with what is already there, which immediately puts it in an entirely different category.

Colas claims that the panels have a lifespan of last 10-20 years, depending on the speed/level of traffic over it, and has even proven that it can handle snowplows (though Colas has stated that drivers would need to “take more care”).

Reality Creates a Roadblock

This solar road project, though, unfortunately relies entirely on those people who seem obsessed with the idea of driving on their solar panels. As long as your response never goes beyond “YAY! SOLAR!” and “hey, roads are just THERE, man,” you likely see this as an exciting step towards a future powered by renewable energy.

Unfortunately, if you’re a person who is really interested in reaching that future, actually thinking about the most practical and economic methods for installing solar becomes crucially important. As such, the continued obsession with this idea of converting road surfaces to solar generation is a horrifying distraction, pulling attention away from the very real advances of the solar industry in favor of an expensive and fanciful pipe dream that will hurt the advance of solar power more than it helps it.

I am not an electrical engineer (like this guy), but the reasons why this concept doesn’t deserve serious consideration are obvious even to me.

Costs of Solar Shrouded in Darkness

The first issue is a simple one: cost. Given the relatively limited resources available for solar installation even in countries committed to its role in their future, getting the most solar capacity for every euro or dollar spent has to be a priority. And in each and every case, solar road projects have completely ignored the issue of cost.

So, let’s review the very basic issues that prevent solar roads from being a viable technology.

  1. Solar panels laying flat on the ground rather than angled towards the sun generate 15-20% less energy.
  2. Protecting the delicate panels from things traveling over them inevitably add cost and typically reduces efficiency even further.
  3. There is absolutely no evidence that a lack of available space has played any role whatsoever in limiting the expansion of solar capacity anywhere in Europe or the United States.

That third item is key. In the event that there was a lack of available space for solar panels, finding solutions for using other areas exposed to the sun could have potential applications. But this simply isn’t the case. Building solar arrays on empty roof space is a much more cost effective method than a solar road is or will ever be. And building utility-scale solar plants is a significantly better option than that.

Dave Jones of the popular EEV Blog and its accompanying YouTube Channel has already thoroughly debunked the solar roads concept, both in the form proposed by the Indiegogo campaign and the Dutch bicycle path SolaRoad. Notably, Jones compared the stated yields of the Dutch project with nearby solar rooftop arrays to show that the project was yielding a fraction of the electricity at many times the cost.

“As the pilot program in the Netherlands proved, with undeniable empirical test results, the best case output of a solar road (when used as just a footpath & cycleway, not even used as a road with its inherent issues) is only half the power output of a typical rooftop solar installation,” he said to in an email. “This fact alone makes it a ludicrous choice to even think about employing solar roads on any mass scale until such time as all available rooftop and other more viable areas are covered with traditional, proven high efficiency, low cost, and very low maintenance panels.”

A Concept as Costly as it is Impractical

The Brusaws continue to get pretty huffy at any suggestion that replacing every road in America might require money in addition to happy thoughts and good feelings. Their response is to not offer any estimate of potential costs and then simply insist that “economies of scale” will make it all work. The Dutch SolaRoad project did reveal a $3.7 million cost for a mere 100 meters, which pretty much confirmed that it was a wildly expensive and inefficient way to generate power.

Unfortunately, Wattway is continuing in the fine tradition of solar road projects in this area. The costs it proposes are much too high to receive any serious consideration from even the most ardent solar advocate.

A look at Wattway’s FAQ section reveals that the company is anticipating a cost of €6/watt-peak for Wattway. For comparison, the installed cost of solar plants in Europe is currently in the €0.80-1/watt range. Rooftop arrays are two to three times more expensive, but costs still typically come in at about half what Wattway is at.

Roadways Can’t Compete with Today’s Solar Options

From this point, it’s entirely unclear how the French Ministry of Ecology and Energy could have arrived at such a catastrophically misguided decision. It appears that a significant lack of due diligence has been done.

French energy journalist Olivier Danielo has been a leading voice in criticizing the project.

“Franck Barruel, head of PV Systems Laboratory at the National Institute of Solar Energy (INES), which is at the heart of this project, told me that no business-model has been studied by Bouygues-Colas for this technology,” Danielo said in an email to “The Energy Return On Energy Invested (EROI) has not been calculated. At this stage, it’s possible that the energy required to produce and install a Wattway plant will consume more energy than this system will generate during its lifespan.”

Danielo also pointed out that the €6/W figure hasn’t been disputed despite seemingly showing the project to be entirely indefensible from a cost and efficiency standpoint.

“The €6 figure has been confirmed by Colas CEO Herbé Le Bouc in the French journal Le Monde, and also by INES,” he continued. “At INES, they think that CAPEX could be divided by a factor 2 in the middle term with industrial volumes. But it will still be far more expensive than ground-mounted PV (€0.8 – €1/W) today, and also more expensive than rooftop PV (€1.5 – €2.5/W).”

So, to review, both public officials and the company that they are working with have confirmed that the project will cost six times as much per watt as spending the same funds on utility-scale solar. They seem to believe that maybe, with economies of scale created by placing a massive order with a single company that has a monopoly on the technology and no competing bids, they MIGHT be able to reduce that price until it’s merely a third as cost-efficient and just 20% less cost-effective than rooftop arrays.

Solar Roadways Could put Environmental Progress in the Slow Lane

It’s difficult to ignore the tortured logic on display here: “If we spend a lot of money on this bad technology, in a few years, it might be almost as good as the good technology we could just as easily invest in today.” Especially so when you consider just how rapidly the cost curve is sloping downward for every type of solar installation. By the time Wattways has achieved its perceived potential cost reductions, the superior rate it’s chasing will likely have dropped as well.

If anything, projects like this stand to hurt the expansion of solar energy, not help it. Craig Morris, Contributing Editor of Renewables International and the Lead Author of, wrote about how the project doesn’t pass the smell test, particularly when so many viable options are readily available.

“My main concern, for the record, is that this project will go forward and then become another Solyndra -- an example of how PV doesn't work or is too expensive,” he stated in an email to “We don't lack the space for PV, so we don't need such extravagances. The crystalline solar we have will get us to 2050. By that time, it will provide power for a few cents per kWh -- quietly, without emissions. What's not to like? “

When asked how the French Minister of Ecology and Energy, Ségolène Royal, could be making such a poorly-researched decision, Morris said, “There is nothing in particular to understand about why the French government wants this except that Royal is a lawyer, not an engineer. The company that will manufacture this particular solar technology is a struggling French firm that could use the business, and as you can tell from the press reports the French public does not yet understand the power sector enough to realize how blatantly bogus this is.”

Dave Jones was equally concerned about how the decision to back this technology might actually hinder the continued deployment of solar power.

“Solar power is still arguably a somewhat marginally viable technology in terms of full ecological production life cycle assessment and financial payback,” he said. “Therefore it is prudent that we (as an energy-hungry civilization) extract the most efficiency, the lowest cost, and the best longevity and reliability for any solar power installation on a mass scale like this. Solar Roadways is a technology that, at best, halves the power output, quadruples the cost, drastically lowers the reliability, and introduces innumerable issues with usage as a road surface. Solar roadways is pure engineering folly."

Solar Roadway Advocates Might as Well be Climate Deniers

The very real advance of solar technology is arguably one of the most important stories for humanity at the moment. As populations increase, and the middle class in China and India rapidly expands, energy demands are increasing at a rapid rate, even as international governments seem to be ready to recognize the incredible peril represented by global warming. Finding a solution that will allow the worst consequences to be avoided means investing all available resource in viable technology.

That’s why it is so deeply disappointing to see the government of France, the nation that hosted the all-important United Nations summit this fall, engaging is such a foolish endeavor. Even the simplest review of this project from an engineering and public policy perspective should reveal it to be a colossal mistake. And yet, critical and limited public funds that could and should be invested in proven solar technology is getting committed to a wildly impractical boondoggle.

As someone coming from a nation where global warming skeptics continue to be able to block important progress despite holding a position that science has repeatedly proven to be utterly indefensible, I find this sort of decision to be wholly demoralizing. Even as American environmentalists are fighting a tough battle over public policy, the French government is opting to provide anti-solar skeptics with more ammunition in the form of a costly and ineffective government program that is wasting public funds. When even the simplest decisions about deploying solar energy can be botched so badly by a major public official, it’s hard hold out hope for the necessary investment in real, cost-effective solar power.

Much as some people love the concept of solar roads, it simply does not represent the sort of innovation that warrants investment. In the meantime, every penny sunk into this absurd idea simply because it’s fanciful and fun is a blow to the continued growth of solar power.

That is, perhaps, the greatest irony of this incredible chapter of the solar story. The advocates of these expenditures are frequently among those that should be green energy allies. They believe firmly in a future powered by renewable energy and want to arrest the progress of global warming. Unfortunately, their willful naiveté has resulted in their energies becoming counterproductive to their ultimate goal.

DISCLOSURE: The views and opinions expressed in this article are those of the authors, and do not necessarily represent the views of Readers should not consider statements made by the author as formal recommendations and should consult their financial advisor before making any investment decisions. To read our full disclosure, please go to:


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