Solar Roads -- Remember These When Environmentalists Accuse You of Being "Anti-Science"

I have written about the horribly stupid but oddly appealing idea of solar roads many times before, most recently here.  As a quick review, here are a few of the reasons the idea is so awful:

 Even if they can be made to sort of work, the cost per KwH has to be higher than for solar panels in a more traditional installations -- the panels are more expensive because they have to be hardened for traffic, and their production will be lower due to dirt and shade and the fact that they can't be angled to the optimal pitch to catch the most sun.  Plus, because the whole road has to be blocked (creating traffic snafus) just to fix one panel, it is far more likely that dead panels will just be left in place rather than replaced.

But the environmentalists are at it again, seem hell-bent on building solar roads with your tax money;  (hat tip to a reader, who knew these solar road stories are like crack for me)

France has opened what it claims to be the world’s first solar panel road, in a Normandy village.

A 1km (0.6-mile) route in the small village of Tourouvre-au-Perche covered with 2,800 sq m of electricity-generating panels, was inaugurated on Thursday by the ecology minister, Ségolène Royal.

It cost €5m (£4.2m) to construct and will be used by about 2,000 motorists a day during a two-year test period to establish if it can generate enough energy to power street lighting in the village of 3,400 residents.

The choice of Normandy for the first solar road is an odd one, given that:

Normandy is not known for its surfeit of sunshine: Caen, the region’s political capital, enjoys just 44 days of strong sunshine a year

Wow, nothing like a 12% utilization to really bump up those returns on investment.

The article follows the first rule of environmental writing, which is to give the investment required or the value of the benefits, but never both (so the return on investment can't be calculated).  This article follows this rule, by giving the investment but stating the benefits in a way that is impossible for the average person to put a value on, e.g. "enough energy to power street lighting in the village of 3,400 residents".  Since we have no idea how well-lighted their streets are or how efficient the lighting is, this is meaningless.  And by the way, they forgot to discuss any discussion of batteries and their cost if they really are going to run night-time lighting with solar.

But, the article does actually give something close to the numbers one would like to have to evaluate another similar investment, and oh boy are the numbers awful:

In 2014, a solar-powered cycle path opened in Krommenie in the Netherlands and, despite teething problems, has generated 3,000kWh of energy – enough to power an average family home for a year. The cost of building the cycle path, however, could have paid for 520,000kWh.

As a minimum, based on these facts, the path has been opened 2 years and thus generates 1500 kWh a year (though probably less since it likely has been open longer than 2 years).  This means that this investment repays about 0.29 percent of its investment every year.  If we ignore the cost of capital, and assume unlimited life of the panels (vs a more likely 5-10 years in this hard service) we get an investment payback period of only 347 years.  Yay!


  1. Ike Evans:

    When I show up to meeting with other engineers, we tend to come to the table with different ideas. Through the course of discussion, bad ideas are tossed out because, well, they're bad ideas.

    Politics is the same way, except the process is much, much slower, and it usually involves some people dying and a lot more suffering before the bad idea is eventually discarded.

  2. Jim Collins:

    I tend to go the other way Ike. We think that this is a bad idea, but there are two groups of people who think that it is a good idea. One group is the people who design, manufacture and install these roadways. The other group is the politicians that benefit by the payoffs from the first group, whether it be cash, jobs or votes.

  3. BobSykes:

    I think the capacity factor would be about 5%.

  4. Not Sure:

    "If we ignore the cost of capital, and assume unlimited life of the panels (vs a more likely 5-10 years in this hard service) we get an investment payback period of only 347 years."

    You didn't mention the value of "Feeling Good About Being Green" to idiots. Factoring that into the equation, it would seem to make the payback period 347 years.

  5. mlhouse:

    Payback???? It ain't their money so why would they worry about a payback period or rate of return?

  6. Q46:

    Here is a puzzle.

    Today in France at 14h22 CET

    Grid demand:-



    Nuclear... 51,42GW (76,93% of demand)

    Hydro... 5,04GW

    Gas... 7,33GW
    Oil... 0,20GW
    Solar 2,57GW
    Wind... 1,84GW
    Biomass... 1,18GW

    Given that France can produce 90% of its demand from nuclear (59 reactors) and hydro, and nuke and hydro emit negligible CO2, why spend taxpayers' money on solar roads and subsidising wind and solar?

    Is any more proof needed that soi-disant climate change has nothing to do with science, just political posturing?

  7. Ike Evans:

    I wonder what the actual numbers would be, but I suspect you would be right.

  8. Ike Evans:

    Bad behavior is generally good politics, I'll grant you that much. But reality is reality, and even Soviet Russia had to face the music after so long.

    I'm sort of glad the French are doing this. It isn't like they are building miles and miles of solar roadways. The small section they are building will (hopefully?) demonstrate reality and they will abandon it as nothing more than an experiment that didn't work like some had hoped.

  9. CC:

    If you simply understand that solar is GOOD and fossil fuels are BAD, then this makes sense. All this worrying about numbers is just boring. (/sarc for those humor impaired).
    But the BADNESS of fossil fuels is so clear in some people's minds (without any evidence) that no measure is too extreme if it will save us.

  10. slocum:

    Yep, those are the 'bootleggers' in the deal, but you forgot all the 'baptists', namely those people (and there are unfortunately a LOT of them) who think it's a great idea because it seems nice and green and futuristic and they're so infatuated that their critical thinking skills on the subject have completely switched off.

  11. SamWah:

    Do the French use studded tires or chains in snow? Will they spread salt on that road to melt snow and ice? What about snowplows? (Waves hand.) Oh, that's NO problem.

  12. herdgadfly:

    I am not sure that the cost numbers of the bike path are well organized. There is first the consideration of the need for the bike path and exactly what a (fill-in: asphalt, crushed stone, concrete) bikeway would cost. Get past the the need perception (which is usually more imagined than real) and you can discover the added cost of the path itself. Now examine the life-cycle of the path (5 years, 10 years, etc.) and you can amortize the cost of the extra spending over the life of the asset. I would expect that the assessment of the reworked data is just as bad as the raw numbers here , but at least the overview of spending other peoples money to help friendly contractors will become clearer.

    Bicycle paths should be paid for by bicycle riders because there is no overall public good in such a project.

  13. What the...:

    The Guardian story links to a Le Monde story that has some helpful figures, likely assuming that this Wattway road achieves its rated output and, based on the cycle path in the Netherlands, that seems extremely unlikely. There is a noticeable lack of reference to cost of electricity from other traditional sources (e.g. nuclear).

    From the final sentence of the penultimate paragraph of Le Monde story:

    Electricity cost (watt-peak; maximum power)
    Tourouvre-au-Perche, Normandy solar road: EUR 17.00
    Roof mount PV solar: EUR 1.30
    Ground mount solar installations: less than EUR 1

    The Le Monde story also mentions an output expectation of 790 kWh per day for the road, which works out to 288,350 kWh per year. This seems wildly optimistic.

    Something to consider is that Wattway is a product of Société Nouvelle Areacem (SNA) companies (the manufacturer of the solar slabs) and Colas (a division of Bouygues, which is a large French construction firm). Best to view this project through a Solyndra lens, but with French taxpayer money ...
    ( )

  14. Jaedo Drax:

    You know we could improve these solar roads by giving them a non-stick coating so that dirt would not adhere to them. /sarc

  15. Jason Calley:

    What would help even more is to keep all the traffic off of them. Maybe the cars could use a service road parallel to it... :)

  16. Tom Nally:

    On YouTube, the debunker known as Thunderf00t has discussed them on several occasions. He's very good at it.

  17. irandom419:

    I see why they want it. It doesn't cover any additional land, so nature is preserved.