Solar Cell to USB Charger

I started building this at the end of the summer (UK). Because my room gets the sun in the afternoon and evening (3PM+). So at night it becomes very hot and wanted to power a couple of fans.
I used 7" (1W) USB fans and even at lower light levels they start to spin, although it needs to be a bright day to have any effect. They can also be folded down and put away if you wish.

The sizes of the cells/mini panels are:
12V, 1.5W, 115mm x 85mm, 12V, 3W, 145mm x 145mm and 18V, 3.5W, 165mm x 135mm