I'm building a small PV system to charge 18v tool lithium ion Ryobi battery packs (both 2AHr & 4Ahr). I have two possible Scenarios that I'm considering.
Scenario #1
PV (87w, 12v) -> CC (PWM) -> Battery (XAhr) -> Load (12v DC "vehicle" charger)
Scenario #2
PV (87w, 12v) -> CC (PWM) -> Battery (XAhr) -> 150w Pure Sinewave inverter (90%) -> Load (85w 120v AC Gang Charge).
Back of the napkin I figure the PV array can supply something like 36Ahr (assuming a 5hr day)
Considering that the sole purpose is to charge the Li Batteries, my basic design assumption is that I'll need to charge 6 4AHr batteries on a daily basis or nominally 24Ahr (4Ahr x 6). If I assume an efficiency of say 90% for the chargers that would work out to be something like 27Ahr. Therefore:
In scenario #1 since I don't have an inverter that's a load of 27Ahr per day (75% of PV).
In scenario #2, based on 90% efficiency of the inverter the load goes to 30Ahr per day (83% of PV)
As this will have long periods of non use I intend to trickle charge while stored.
What size and type of battery should I be looking at? Do I even need a battery?
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