Article on "Well to Wheel" efficiency, and points out that while from plug in to use Electrical vehicles are more efficient by a factor or 3, if you look at it from the Well to use, it is dead even given the greater loss of energy just producing the electricity AND the loss of electricity as it is used to charge the batteries (Thus direct wire hookups, as used on LRVs and Trolley-buses exceed both diesel powered vehicles AND Hybrids that rely on batteries).
http://en.wikipedia.org/wiki/Well-to-wheel#Well-to-wheel
http://en.wikipedia.org/wiki/Electric_vehicle
Article on Solar Powered Vehicles:
http://en.wikipedia.org/wiki/Solar_vehicle
The volt carries on it 16.5 Kilowatt hour (kWh) of electricity storage capacity. As a test people installed Solar Panels on a Prius and was able to produce 215 watt per hour and thus extend the electrical range about 20 miles per day (Given that the power is used up in 20 minutes in a Prius that is NOT much).
http://www.chevrolet.com/volt-electric-car/features-specs/options.html
Please note the Volt has an electricity only range of 38 miles, almost twice as far as the Prius , thus will the addition of the Solar Panel we are talking about 58-60 miles tops. Given that most trips are below 50 miles, may be sufficient. For people who need longer range (for example, the population Center in my County is 20 miles away from the County seat, where the court house is located, thus I have to travel 40-50 miles a day on any day I have to go to the courthouse PLUS my commute from my home, thus something with a 58-60 miles range, WHEN IT IS SUNNY, 38 on all other days is not usable by me. The better option for me would be a high mileage small engine car, like the Chevrolet Cruze.
In short, except in areas with more sunny days then over cast days (Southern California and other desert areas), the addition of a Solar Panel on top of an electric car will probably NEVER pay for itself, and worse due to the additional weight being hauled around, may actually reduce the range of the vehicle on overcast days or if one drives at night (Through this excess weight van be neutralized if you make the car panels the solar panels, increase the cost of such body parts, but minimize the gain in weight).
Furthermore of marginal use in any vehicle that goes more then 50 miles a day, for example tractor-trailers. Great Idea, been done, but if you look at the numbers of marginal usability. Possible to go clear across the US is a Solar Powered car, at 20 mph and travel only during daylight hours (and then in the summer without A/C, see wikipedia above that mention that this is possible). The problem is NOT that installing Solar Panels in a Car is possible, the question is such an installation worth it? Unless people start to accept lower performance in vehicles (i.e. fully willing to go 20 mph on the interstates) the answer is NO. On the other hand if people are willing to accept such reduction in performance, then it is a possibility (but then, human powered vehicles, i.e bicycles, may just pass such solar power vehicles up). I am afraid the Solar power vehicle is headed for the worse possible of graveyards, Caught between two technologies that it is superior to it in some ways, but in their own niche Superior to Solar Powered Cars.
Being Caught between two other technology is a graveyard, The best known example of this is the Stirling engine. The Sterling was a more efficient external combustion engine that could burn anything but losses out to the Steam Engine (And the later Steam Turbine) when heavy power was required AND to animal power (and the internal combustion engine) when constant power was NOT needed but some power was needed. The Sterling is still is use, but in very narrow range of uses due to the fact what it can do well, no one else can do as well, but people who want to be able to use MORE POWER OR QUICK Power on demand, opt for some other power source.
Solar Powered Cars seems to be heading down that same road, not enough power being generated to compete with charging based electrical system as in the Prius and the Volt, but requiring more care and money then riding a bicycle on the other end of the spectrum. It may survive as a supplement to a charging based system as on the Volt, but even they it will be marginal except in desert areas.
One of the problems would be a better option then Solar Panels on the Car, would be to park the car in a Garage with solar panels on the Garage. Such a Garage would provide more area for the Solar Panels and when the car is out, the electrical panels on the Garage can charge the house or some other electrical storage system till the car comes back and gets plugged back in.
http://en.wikipedia.org/wiki/Stirling_engine
http://www.chevrolet.com/volt-electric-car/features-specs/options.html
Just some comments why the Solar Car will always be with us, and will always be a "Few years aways". It is headed for a very narrow niche that people in that niche will opt for plug in or bicycles instead due to each covering the niche (poorly compared to the Solar powered cars, but covering it) AND covering their own niche without even a threat of the Solar Powered car competing in their niche. This is what happened to the Sterling engine and I am afraid the Solar Powered Car is headed for the problems the Sterling faced, caught between two Superior technologies, each capable of doing the niche the Sterling (and today the Solar power car) was in, but poorly, but the Sterling (and the Solar powered Car) doing even worse when used in the niche of the other two technologies.
Note on The Chevrolet Cruze and Volt, both were developed at the same time, to use the maximum number of interchangeable body, frame and interior parts. For every Volt GM intends to sell it plans to sell 10 Cruzes (And this seems to be the numbers GM is operating in, GM sell roughly 10-11 Cruzes to every Volt). In fact if you look at a Cruze and a Volt and ignore the paint job that says one is a Volt, you can NOT tell the difference from the outside OR even riding it. The exteriors and interiors are the same. The difference is in the engine, transmission and Trunk. The Cruze comes with a 1.7 liter engine, the Volt a 1.4 liter back up engine (if you opt for the Eco version of the Cruze, you get the same 1.4 liter engine as used in the Volt, but it is Turbocharged in the Eco). The Volt uses its engine to re-charge the battery when they run low, thus is nothing more then a generator, thus does not need to be turbocharged. The Cruze has a much larger trunk, for the simple reason the Volt's Batteries had to go some place. The transmission is front wheel drive in both vehicles, direct electric battery drive in the Volt, through a transmission in the Cruze.
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I can think of a lot of things one can do with preheated oil. That too is a dream of mine. When you are solo it just becomes all about minimalism. Peace. lmsp
