I think you make some good points
that gives a maximum of 5W
I’d say less than that, probably more like 1W @ 5v in the real world.
3) you're disaggregating the storage-and-charging functions from the Lantern
It seems to me there are two separate ‘modes’ to the device.
Grabbing data from space approx 0.5w @ 5v
Providing data over Wifi to local devices: additional 1-2w
We have established that given the form factor (or budget) it’s not possible to build a in built solar/battery system that does both satisfactorily.
However I do think it could do 1) directly solar powered, for much of the world, for much of the year. Making the device direct sun powered would involve putting a capacitor in it and a simple circuit to boot the device when enough power is received & shut it down cleanly off the capacitor when voltage grops.
So install 1w of panels @ nominal 8v, set the device to boot at 6v & shut-down at 4.5v.
Then put a usb socket in the side of it for external power and people can sort out whatever solution they want for 2) (including not bothering and swapping the sd card between lantern and phone)
Robust solar power systems are a well understood technology. I’d suggest a partnership with people who already do this would make sense, rather than trying to fix both the ‘data from space’ & ‘remote power’ problems at the same time
I’m a fan of: http://www.solar-aid.org/how/ & think they’d make a good partner.
Standards for lights/ charging stations are defined: