It's an interesting idea, and not poo-pooing it by any means (all great ideas get mocked at first), but seems cost prohibitive. It's fine to say 'it pays for itself' - but how does it 'pay for itself'? It's one thing to create panels that are both solar batteries and can serve as building materials, it's something altogether to build the infrastructure to collect and use that energy. And what about reliability? Asphalt doesn't do anything, other than last for decades with very minimal upkeep requirements. You trying to tell me that these panels are going to have anything close to that kind of durability and sustainability. I'm very skeptical that this could really be practically put into place anytime soon.
I think replacing all roofing materials with solar versions would make a lot more sense, as it would be much easier to harness the energy collected for practical home purposes... I think that kind of paradigm shift, away from shingles to solar roofing materials, could happen very soon and make a big difference in energy use. Building roads with solar panels - seems a lot more challenging just at a glance...