I am not missing the point, I'm bang on. Only an idiot would put solar panel on the road instead of on roofs and poles.
In my opinion the whole point there is not that it´s solar panels, but the road part of the "solar road". Therefore it´s funding of ...
roads. The municipal areas probably promise themselves or imply "free road maintenance" by using solar panels funded by private investors plus some tax money, instead of tarmac. Maybe the model is based on some strange butterfingering via the energy produced.
To investors such a project might be presented as a solar farm, calculated by their expected values. To the city it is a road. To the tax payer it is a futuristic thing/new street lights that kind of vibes/implies compatibility with electric cars. What is done there is a mix of concepts and neglection of downsides (like lack of redundancy, electrical supply/grid suddenly becomes road).
So if something breaks, they don´t fix the pothole, they exchange the panel after all, which is then - road maintenance(?), electrical work(?), warranty case?. All they need is a manufacturer unwise enough to guarantee their specs for a road grade panel. Which - given the grooves that heavy trucks do leave in roads (even those up-to-spec) after some years - sounds quite adventurous, even with a concrete base that has it´s own issues. Compensation strategies, like disallowing the users that do cause damage to protect the panels, kind of does not serve the purpose of saving you from cost. It skews the calculation because the damage is then done elsewhere and more concentrated than before which a city needs to pay for as well. You can´t lock out a whole city from road based freight transport.
Probably private investors usually would not invest in a typical, public tarmac road or in fixing potholes, but burning it in a solar installation project seems to sound better.
I assume they only got that far because you can always juggle the numbers between road installation cost, road maintenance, energy output and tax money to make the calculation look good by throwing all costs in the same pot and claiming to compare to that, problem is, it isn´t competitive in any of those. For a solar farm it is too inefficient by design (they didn´t reinvent the solar cell itself), for a road it is too expensive to build and maintain and too complex in structure. All thats left is an impression of a futuristic design, but it is not durable enough for that to last a certain amount of trucks rolling, braking, accelerating on it all year long to keep that impression before it became self financing.
Admittedly the idea itself sounds very compelling (sunlight is quite cheap), but having the solar cells above or next to the road would make a lot more sense in terms of durablity, ROI and financing of roads. Probably does not work that way in the US, where whole houses are transported on streets.
Population density comes with more traffic and therefore more infrastructure and therefore less unused space. I don´t see a reason to exaggerate such considerations as long as there are more viable alternatives. So roof installations, installing it in less constrained spaces like bike ways or pedestrian walkways or seperate solar farms are usually the way to go, if seen from the energy production point. Even if there was a magic bean that turns roads into ever lasting constructions, then a) it could be used to build any road that way b) consider the job loss for road maintenance. As long as that is impossible, roads and infrastructure itself probably needs to be cheap or at a certain price/performance ratio and kind of separated to stay redundant and good in it´s core purpose. E.g. a typical accident spills quite some liquids on the ground, i wouldn´t assume that to be spec´d into a solar panel and have a super road that is good in everything.
Same goes for things like inductive charging in roads, altough more simple, but still a mix of concepts, adding up the downsides.