Regarding Charging (SOLAR PV) while LOADING 48V... does it affect SOD AND DOD?

There are several basic things that help extend battery life... Discharging to 50% maximum (do not go deeper if you can avoid it), recharge reasonably quickly (something like 10% to 13% rate of charge), when discharging, try to go to at least 25% discharging (75% state of charge--shallow discharging is not good for lead acid batteries), keep batteries cool (hot batteries, shorter life). Monitor electrolyte levels to prevent exposing plates to air (oxygen) and use distilled water (filtered rainwater, etc.) when refilling batteries. And avoid "over equalizing" your battery bank (equalizing generates heat in the battery bank, "uses water", the bubbles can erode the plates, and the oxygen which forms on the positive plates can cause plate and grid corrosion.

When operating in Hybrid mode--The solar panels do supply power directly to the GT inverter--However, the battery bank does act like a "capacitor"--For single phase inverters, because your inverter is outputting power at 60 Hz (or 50Hz outside of north America), it is drawing power at a 120 Hz "pulse train" (really a sine squared wave form). If you measure the battery voltage, you will see the voltage change by a few tenths (or more) of a volt at 120 Hz. If your battery float voltage is too low, it is possible for the "discharge pulse" to take the battery bank into a "micro discharge", and then a "micro recharge"--Which will cause the battery to fail sooner.

If your system does go Off Grid (utility fails), you discharge the battery bank (to 75% to 50% state of charge typically)--When the sun is up and your bank is charging (while still off grid)--Then your solar panels are supplying power to both your AC loads and Battery Charging at the same time--Nominally, for an off grid home, they usually charge the batteries during the day (sun is up), and discharge at night--So your solar panels quickly and properly recharge the battery bank (10% rate of charge nominal recommendation).

If you have daytime loads (business, busy house during the day), then your "base loads" do take some percentage of your solar array's output and may prevent the batteries from being fully/completely recharged during the day (if your array is 10% rate of charge, and your base load is 1,000 Watts out of a 1,500 Watt array, then your charging current is roughly 3.3% of battery capacity. Way too low for a "comfortable" battery recharging current (long term grid outage or being full time off grid).

Since batteries are expensive and solar panels are "cheap" these days--If you have a large base load and are trying to prepare for a long term grid outage/off grid event, then I would suggest your "ideal array" be 5-10%-13% rate of charge 10%+ rate of charge for full time off grid) + additional array wattage to carry your base load.

Part of it depends on how deeply you cycle your battery bank--Lead Acid batteries really work well for daytime charging and night time loads. If your profile is reversed, you may get away with a 5% effective rate of charge (day time loads, very little night time loads, so battery bank does not cycle deeply during normal use). And when you have a couple cloudy days--You can always fire up the genset to assist with charging. (many people prefer to add solar panels and keep generator use/fuel storage to a minimum).

Does this help?

-Bill