I think several of us are possibly being a bit absolutist in thinking. Certainly the highest currently available commercial efficiencies in solar panels are around the Sharp triple-junction at 37.9%. The latest developments seem to show Perovskite layers could add as much as 50% to efficiency, assuming the durability and other issues can be resolves, so might end out with commercial efficiency of more than 50%. Assume that happens, still a car will not have enough space for that to be useful in most populated latitudes.
Think a bit differently though. Say, an over the road truck, operating in areas near equatorial, with a long trailer or two. Then you'd have copious space, operation with high sunlight intensity and fairly controllable use variables. That could make enough difference to be highly useful in some conditions.
Even being optimistic I do not think it is likely that we'll have solar powered surface transportation within the next decade. I am confident that we will see special purpose solar powered aircraft within the next decade.
I will happily wager that we will have some disruptive technologies in this are within the next decade that we do not currently see. Among the candidates:
1) superconduction at normal operating temperatures that will increase operating efficiency of BEV's by 10% or more;
2) when combined with other measures to reduce internal resistance through batteries, connections, inverters, straight DC, motor redesign and so on I fully expect to see the same sort of efficiency improvements that we have seen in turbine and ICE engines, i.e. 5-7% per annum.
3) increasing energy density coupled with reduced total weight using lighter materials ought to be good for another 2-4% per year;
4) improved material such as carbon fiber nano-scale reengineering improvement to a wide variety of metals should be good for at least 3% per year improvement.
If we, following the path of battery development since li-ion, the auto industry in the last decade, and aerospace in the last three decades it seems those projections probably are realistic.
of those things happen, then solar cells on cars might do more than look pretty on the Fisker Karma. In the meantime solar power in stable locations is now a quite sound economic decision in residences, industrial plants and Superchargers.
So, yes, there will be some solar panels on transport vehicles of some sort within the next decade.
Now, I will record my predictions and will happily make book that these things will happen one way or another.