You should also be aware that standard USB cables are *not designed for high power applications*. See this discussion for example: https://electronics.stackexchange.com/questions/170292
Given the tiny wires in a standard USB cable, it really should be limited to 500 mA (two Octolively panels). If you have a special cable rated for 2 A of power, then you can power up to 10 Octolively panels. However, you should also make sure to check what the maximum current draw allowed on your USB power bank is. Not all are rated for that much current.