So, if there is no PWM in the BMS, then are you just connecting the PVs to the batteries on and off? If this is so, how do you achieve the various segments in the charge cycle?
Lithium cells require only cc and cv charging that is if you want to take advantage of the battery entire capacity and do not care as much about the cycle life.
For long cycle life you can only use one stage the cc ( bulk ) charge.
The most common Lithium cells used in most portable electronic devices and recently electric cars will only charge up to 85% if you are using just one stage cc charging (you stop the charging as soon as the voltage gets to in this case 4.2V).
If you do that you almost double the battery life cycle while you are losing about 15% of the stated capacity. Since in mobile electronics energy density is important that 15% is way more important then cycle life that is anyway good enough for this type of applications.
I recommend and use LiFePO4 batteries for stationary solar energy storage systems and those will charge to at least 95% with just a single stage charging cc and have a much better life cycle than the more common Lithium-ion mentioned above so cost amortization over the life of the battery is way better.
Typical LiCoO2 cells (usually found as small 18650 cylindrical cells) will last 500 cycles at 100% DOD and if charged with just cc up to 4.2 they can do 700 to 1000 cycles while just around 85% of capacity is available cost in volume is at around $220/kWh
So for a 1kWh battery 500 cycles x 100% x 1kWh = 500kWh over the usable life of the battery $220/500kWh = 44 cent/kWh stored (this is the theoretical amortization cost of this battery charged with cc to 4.2V and cv until current drops to 0.02C)
If the same 1kWh battery is charged with cc only 800 cycles x 85% x 1kWh = 680kWh better than first case $220/680kWh = 32cent/kWh
LiFePO4 costs more at around $400/kWh but you can find large cells hundred of Ah capacity and can last 3000cycles at 100% DOD (even 6000cycles for quality Sony cells) and around 7000cycles at 70% DOD for Winston cells that I usually recommend for solar storage
So same 1kWh capacity will be 2x as heavy as a LiCoO2 so not good if energy density is important but 7000 x 70% x 1kWh = 4900kWh so $400/4900kWh = 8 cent/kWh and the life of the cell is probably 20+ years in typical solar application.
In real life you will not be able to use 70% of the battery capacity every day so over 20 years (about 7000 days with one cycle every day) with an average of 30 to 40% DOD per day you can not realy get to use 4900kWh but still it will be close and probably real life cost of storage will be around 20 to 30 cent/kWh still will be way better than LiCoO2
Sorry for the long explanation the idea is that in stationary offgrid storage cost of storing each kWh over the life of the battery is important and for that you need to only use cc charging so stop the charging as soon as the cell gets to the set level 3.55V for LiFePO4 or 4.1V or even 4V for long life using LiCoO2 the PWM or other methods of constant voltage charging will be detrimental to battery life.
Since last time I wrote here the new SBMS model was done. Here is a video I just uploaded about the last version if you are curios