Size to power trade off with solar panels
This is dependent on what you are willing to pay. A remote controlled car pulls Amps of power normally, you will not be able to sustain this with a solar panel you can afford and is not too large.

If you want to use a solar panel for recharging the battery during down time this is very possible.

Solar panels are based on a watts per square inch they can achieve. They are still normally sold with a wattage rating.

The amount of available power is quite variable. Most marketing give you an absolute best case. Things that cause great variance are...


Alignment to light source. Yes,
being off-angle from the sun is bad.
Amount of light available. Small
variance of conditions can have a
large affect.
Light source. florescent and the sun
are very different, there are panels
for each.
There can be many more variables, but these alone will account for  you getting less than 10% of what it is rated in most cases.


If I get a chance tomorrow I will look up more information for you.