How to convert battery powered roller blinds to be solar powered?
A solar panel by itself isn't a charge controller.  It will keep putting out whatever voltage and current it can.
NiCd cells are pretty tolerant about being overcharged at low currents up to about 0.1C, where C is the capacity of the battery in amp-hours (or milliamp-hours).  So you could trickle charge an 800mAH pack of cells at 80mA.  However, NiCd cells are harder to find these days, because they contain toxic cadmium.
NiMH cells are much easier to find, but don't like being over-charged and need a proper charge controller.  If you constantly trickle charge them all day, they will soon fail.