French solar roads – silly walks

France’s environmental minister Ségolène Royale is rolling out 1,000 kilometers of a technology that will both be bad solar and bad road. Craig Morris critiques.

(Photo by Craig Morris)

(Photo by Craig Morris)

Despite plenty of warnings, the French government is going ahead with a costly, wrong-headed project that will unjustly give solar a bad reputation. When this project is finished, expect reports on how “solar is expensive” to reference the price tag of French solar roads.


Apparently in need of a showcase project, the French government is throwing its full weight behind the idea, with a lot of videos embedded on its own press release (in French), which is quite unusual.

French solar expert Olivier Daniélo is having none of it. Repeatedly, he has shown that the numbers the government is using do not even add up. For this report, he told me:

“It’s deeply false. 1 km of road with solar 2.8 m wide is equivalent to 2,800 m2 of PV. That comes out to a mere 340 kW for the entire kilometer of road, and Royale says that’s enough for 5,000 households. But a French home needs more than 68 W of PV!”

(Note that it’s unclear whether the solar part of the road 1.8 or 2.8 m wide; reports conflict.)

The problem is that solar has a capacity factor of around 10% in France (the number is rounded off; let’s keep the math simple). It’s dark half the time, cloudy a lot, etc., so a panel rarely reaches its maximum output. If 62 W is available per household at a capacity factor of 10%, we are talking about the equivalent of 6.2 W constantly – enough, as Daniélo puts it, “to power a single small lamp.”

Daniélo also previously pointed out that reports of a possible 17,963 kilowatts-hours of electricity from a kilometer of the road (such as this report in French, where the error was subsequently corrected thanks to him), were wildly off the mark – a more likely daily output is 790 kWh. Estimates of the road’s power production potential were thus 24 times too high (also see PV Magazine’s report, which calls the initial estimate “bizarre”).

We also know that the price tag is 5 million euros (report in French). And we know that 50 households are to be served, putting the price tag at 100,000 euros per household. Keep in mind that, as Daniélo points out above, those households will in no way get all of their electricity for that money, but it’s an improvement at least; the Dutch spent 1 million euros per household for their solar bike lane.

Might this project lead to affordable solar roads in the future? A new report in the Financial Post (which recently mistook big German utilities for the drivers of the Energiewende, not the obstacles) says that the French company already has plans for new solar roads in Calgary and Georgia. But the report closes with the warnings of a Bloomberg analyst: “On roads, I don’t think [solar] will really take off unless there is a shortage of land.” And, one is tempted to add, a shortage of roof space.

What this new project in France demonstrates most of all is that French decision-making structures do not have enough internal review mechanisms. “Is there really no one within the French Environmental Ministry who understands that at least 6 euros per watt for just the panels is an awful deal?” Daniélo asks. In comparison, roads could be shaded with solar – put solar on stuff, not stuff on solar – at a cost of only 1.5 euros per watt, and ground-mounted arrays now cost less than a euro per watt in France.

In order to build nuclear, France relied on its elite system of experts, which tolerates no outside criticism; if you want to have a career as an engineer in France, you toe the line. We will also probably (and unfortunately) see solar roads going up in other jurisdictions (like the Netherlands, Calgary, and Georgia) that have little experience with solar. Furthermore, politicians need showcase projects like this, and the public is far, far too eager for technical breakthroughs – the news that the wind turbines and solar panels we currently have are good enough just isn’t sexy.

Notably, this solar road garbage is not (yet) planned in Germany. The country probably has enough experienced experts to stop this, many of them in the general public.

But please, don’t take my word for it – here’s the Australian video blogger on the French Silly Walk:

Finally, solar roadways are not just bad solar, but also bad roads:

A silly walk, indeed.

Craig Morris (@PPchef) is the lead author of German Energy Transition. He is co-author of Energy Democracy, the first history of Germany’s Energiewende, and is currently Senior Fellow at the IASS.


Craig Morris (@PPchef) is co-author of Energy Democracy, the first history of Germany’s Energiewende.


  1. Edmund Wood says

    “…the price tag is 5 million euros… we know that 5,000 households are to be served, putting the price tag at 100,000 euros per household.”

    Surely this is a case of ‘the pot calling the kettle black’ and you have got your own dose of false accounting here? I make it only 1000 euros per household.

  2. OD says

    Dear Craig,

    You write:

    “We also know that the price tag is 5 million euros (report in French). And we know that 5,000 households are to be served, putting the price tag at 100,000 euros per household.”

    It’s wrong. Here the good data:

    “In fact, Segolène Royal, French Minister of Ecology, announced that one kilometer of the solar road will deliver enough electricity for 5,000 houses. This is also wrong. With 767 kWh per day – official data from Michel Salion – it will just be able to power 50 French homes. The cost of one kilometer of the solar road is EUR 5,000,000, which works out as EUR 100,000 per each home that is powered by the road.”

    Olivier D.

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