I'm not seeing it happen any time in the next 50ish years, maybe longer or even not at all. There are a handful of reasons why I can see this idea failing:
1) Cost. This will be an extremely expensive project that will require constant maintenance. How will they combat wear and tear due to environmental damage, tire damage, oil, etc.
2) Efficiency. Once the roads get some use and are covered in dirt, tire rubber, oil, etc. will they still be efficient without an incredibly budy maintenance program? Oh, with a heavy maintenance program will the roads still be able to be used as much as current roads?
3) Environmental. Every winter roads are salted, sprayed with brine, plowed, or otherwise treated somehow for snow and ice. How much can these roads take before a bajillion dollar "Solar Freaking Roadway" becomes an expensive plastic and silicone road that no longer produces electricity?
4) Technology. Who's to say that we will have road driven vehicles 50-75 years from now? How long do these roads need to be in operation for them to pay off? I'm not suggesting that we will have flying cars but you never know where technology will take us and these roads will have to be around for a while before they pay for themselves.
5) This one is kind of a reach but I have been told by multiple people that solar panels are a scam. For one, they take much more electricity to build a solar panel than what they will produce in their life time. Second, the savings a solar panel will net someone will barely pay for the purchase price of a solar panel by the time the panel has reached its life cycle. I say this one is a reach only because I haven't ever dug into the legitimacy of these claims but I have heard it from more than one person.
I think "going green" is a great thing and taking better care of mother earth should always be a priority in everyone's mind. I'm not a tree hugging hippie but I don't like to shit where I sleep either. Maybe some day there will be a more efficient roadway but the solar panel roads are nothing more than a pipe dream for some people.