That's a very good question.
If you are using an EF110W solar panel we don't suggest you use 1 or 2 sets of it as it will take a very long time to charge the unit fully. We suggest using a minimum of 3 sets. If you use 3 sets of EF 110W solar panels it will take 7.5-15 hrs, and if you use 4 sets of EF 110W solar panels it will take 5.6-11.2 hrs.
As for using EF160W solar panel to fully charge the unit, if you use 1 set it will take: 17-34 hrs, if you use 2 sets it will take: 8.5-17 hrs, if you use 3 sets it will take:5.6-11.2 hrs, and if you use 4 sets it will take: 4.2-8.4 hrs.
Lastly, if you choose to use EF 400W solar panels, we only suggest using 1 or 2 sets but not more than that as it doesn't support more than 2 solar panels input. Using 1 set of EF 400W solar panels will charge the unit in: 6.3-12.6 hrs, and using 2 sets will charge it in: 3.2-6.3 hrs.
Please keep in mind the solar charging time provided above is only applicable to EF solar panels and if you are using a different brand of solar panels the timing will vary.
Hope this was helpful :)