Very rough, off the cuff numbers: let's say you have a huge 100W portable solar panel, let's assume it's magical and has 100% efficiency, let's also assume that you live in a land which gets sun for 12 hours a day every day, in an average day you're going to make 1.2kWh. Let's also assume that roughly 75kwH is usable in an 85kwH battery, so you can charge ~4 miles in a day.
When you factor in realistic numbers and inefficiencies, you're probably looking at 1mile a day, totally not worth the hassle for a portable solar panel (if it was even doable).