How could i connect a 18650 Lion to be able to supply my embedded device while charging?
As Finbarr says - a BMS should NOT be used as a LiIon charger.
Even if the cutoff voltage at full charge is correct it has no mechanism for formally implementing and terminating the "CV" portion of the charging cycle. 

You need to specify 


The PV panels Wmp, Vmp and ideally anything else you know about it.
The battery mAh.
Brand and model a useful bonus.


In many cases the arrangement that you have shown but using a proper LiIon charger is "good enough".  

With no load, if the PV panel has enough capacity the charger will charge at designed Imax.
If the load draws current 


The charger will supply current to the load up to a max of Imax or whatever the sun allows at that point.    
Load current above that level will be provided by the battery.  
If the load draws less current than the PV panel can provide the charger will use the difference to charge the battery.  
The only point where some "dancing" will occur is if the panel can provide more than the load requires and the battery reaches charge termination point. The charger will cease providing the load - the battery will seamlessly take over supply - battery voltage will drop - the charger will at some point restart charging and this cycle will then repeat. This will probably work without problem, except that the constant battery cycling (albeit over a small range) will add a little to 'wearing it out'. In most cases this will not be a problem.




A suitable charger would (probably) be a TP5100 eg see here. Up to 2A charge, 1 or 2 cells, up to 18V in.

TP5100 datasheet