Under ideal conditions, solar panels generate approx 15 watts per square foot or .1 watt per square inch. Determine how many watt capacity your battery pack is and google will assist you with the math from there.

Now I am sure my calculations are way off but first run-through for a 1 Sq/Ft panel, you would need to have 127 peak sun hours to charge a Specialized Creo e-bike. Hopefully, there are some smart engineering types who point out how wrong I am but its a start.