If you want some interesting reading, look back through popular science magazines for the last hundred years or so and see how often articles pop up regarding how new tech should allow us to power everything by solar in the next 10 years or so. The articles from the 1800's read very similar to todays articles.
Problems still needing to be solved. Efficiency of solar energy collection. Solar panels are still very inefficient, and you need a significant surface area to collect significant power, especially during less than optimal conditions. Battery storage is the biggest issue though. Batteries have only made small incremental improvements over the years, with the newer technologies relying on raw material that aren't readily obtainable should we try to go into very large scale production. We're also no where near the point where we have the capability to store in a size/weight package enough energy for high use things like HVAC, or propulsion of heavy non aerodynamic vehicles.
Who can predict what new technologies the future holds. That said, somehow I doubt I'll see anything close to a self sustainable vehicle that I would consider practical popping up prior to RVing as we know it being banned, regulated out of being, or driven out of existence by economic reasons.
