I didn’t go into the calculations, just have been constantly scaling up until it starts working 
The tomo didn’t arrive. I’ll get both the 2x and 4x version however in the meantime I’ve just received my new Xiaomi 20000mah Power Bank:
Took 7 hours to charge but now ready for some experiments. It also accepts pass-trough however when a power source is detected there is a little interruption which causes the Xiaomi camera to restart itself.
As for solar panel, yes they are probably also underscaled.
I have 2x 21W (anyway cannot connect both at the same time or do a serial mount, there is again probably an adapter or something which allows to connect 2 usb power source to have 1 output with more power but didn’t look at that yet).
This is what i’m using:
By themselves one of them is enough to power the Xiaomi cam (of course when they are on sun :))
But I have enough material to start playing a bit. I’m still waiting for my usb power multimeter:
http://www.ebay.com/itm/YZXstudio-ZY1271-Colour-TFT-Dual-USB-Power-Monitor-QC-3-0-Dual-Type-C-Micro-USB-/132104417161
To be able to monitor the “real” consumption and output at different stages.
but the bigger solar panel you’ll have to more “loss” you can afford not being full sun optimal exposure.