Coyote Blog

Long-time readers know that solar roads are like catnip for me -- I can hardly think of a better example of a technology that makes absolutely no sense but gets so much passionate support and funding.  If you are not sure why, here is a primer on why they are predictably awful.

So it turns out that the solar roads I was sure would not work have actually now been built and... they don't work.

One of the first solar roads to be installed is in Tourouvre-au-Perche, France. This has a maximum power output of 420 kW, covers 2,800 metres squared and cost €5 million to install. This implies a cost of €11,905 per installed kW.

While the road is supposed to generate 800 kilowatt hours per day (kWh/day), some recently released data indicates a yield closer to 409 kWh/day, or 150,000 kWh/yr. For an idea of how much this is, the average UK home uses around 10 kWh/day.

The road's capacity factor – which measures the efficiency of the technology by dividing its average power output by its potential maximum power output – is just 4 percent.

In contrast, the Cestas solar plant near Bordeaux, which features rows of solar panels carefully angled towards the sun, has a maximum power output of 300,000 kW and a capacity factor of 14 percent. And at a cost of €360 million, or €1,200 per installed kW, one-tenth the cost of our solar roadway, it generates three times more power.

There is much more.  I am embarrassed to say that when I slammed solar roads all those years, I actually was missing an important problem with them:

Unable to benefit from air circulation, its inevitable these panels will heat up more than a rooftop solar panel too.

For every 1 degree Celsius over optimum temperature you lose 0.5 percent of energy efficiency.

As a result a significant drop in performance for a solar road, compared to rooftop solar panels, has to be expected. The question is by how much and what is the economic cost?

I will add this to the list, thanks.

When I write stuff like this, I get the same kind of mindless feedback that I get when I point out operational issues at Tesla, ie "you are in the pay of the Koch brothers" or "you have no vision."  Well, I am actually putting solar on my roof and will get (hopefully) 45,000 KwH per year, which is about a third of the energy they get from this road but installed for a bit over 1% of the cost of the road.  And the panels are all ideally angled and placed, they are up in the air with absolutely no shade on them at any time of the day, and they don't have any trucks driving over them.