Hi Lloyd,
Boy, I'll try to answer all this the best I can.
I have two Morningstar MPPT controllers on the solar arrays that keep track of their power. I have a Doc Wattson with an external shunt on each wind turbine. I have a regular old utility kWh meter (an old one with gears and the big wheel in it) between the inverters and the main panel. That old meter does not have the dials on it - it has numbers on it like a car speedometer and it only shows our usage in increments of 10 kWh.
On the voltage drop issue, the wires from the bank to the bus are only about 4-5 feet long. At the full 375 amps that the inverters can draw, there's only a little over 60 amps flowing in each of the #2 wires, which is well within the safe limits for #2 cable at 4-5 feet.
The wires to the inverters are a little longer - about 10 feet. Those come from the bus and are 4/0. All the turbines and the solar arrays feed the bus.
Voltage control on the bank is done with two methods - I have Morningstar MPPT controllers on both solar arrays, which handle bulk, absorption and float charging. And I have a Morningstar RD-1 Relay Driver that turns on water heating elements in the water heaters to control excess power from the turbines. The primary water heater's bottom 2,500 watt element is on all the time and has a thermostat on it set at 125 degrees. That provides us with 55 gallons of water at 125 degrees at all times. The top 2,500 watt element in that heater is turned on by the RD-1 if the bank reaches 30.0 volts and the thermostat on that element is set at 170 degrees. The top element (also 2,500 watts) in the water pre-heater comes on at 30.5 volts and its thermostat is set at 125 degrees. The bottom element (2,500 watts) in the pre-heater comes on at 31.0 volts and its thermostat is set at 170 degrees. If both water heaters are hot and no auxiliary heating load available (happens very rarely) I got a second RD-1 that shuts the solar arrays and turbines down in stages starting at 31.7 volts. It shuts the solar arrays down first to prevent the open voltage on the arrays going over 150 volts into the MPPT controllers, then it shuts the turbines down. When the voltage comes back down to safe levels, then it fires the turbines and solar arrays back up.
I have never measured the voltage at the batteries with the inverters fully loaded. I just go by what the inverters say they see for voltage and I know I can load them at 7.5-8 kw and with a fully charged bank the voltage stays above 24. The inverters show actual voltage and compensated voltage, and I always look at the actual voltage.
Yes, when the gen is running it uses the inverter's chargers to charge the bank.
Every two months for the last seven years I fully charge the batteries on a poor power day with the generator, then pull each battery out and test it and service it. I leave the house on gen power so there's no load on the inverters or bank, then I put a piece of masking tape on the battery and hook up my Sun AVR to it. I record the at-rest voltage, apply a 25 amp load for three minutes and record the loaded voltage, then let the battery recover for one minute and record the at-rest voltage on that piece of tape. The numbers I like to see, respectively are 12.85, 12.35, and 12.65. That tells me I have a healthy battery. I just serviced our new bank for the first time about a week ago. Every battery was just about dead on the nuts perfect. None of the readings varies by more than about .03 volts between the different batteries. That tells me after two months in service they're all pretty equal and there's nothing bad happening with my wiring system to get them out of balance.
I'd really like to keep all the batteries in one bank to simply it. Having to manage two banks would be a pain. If it's best to connect the new ones like I got the old ones connected, I'll just buy the extra wire to do it. I was just wondering if that was necessary, or if could add them in pairs to the six groups I already have. I got these 12 batteries for $310 each, including truck freight to my door. For that price, and the additional 16,000 watt-hours they can store pulling them down to 50% SOC, I figured I couldn't go wrong. And it will improve my heavy load times like when my wife runs the clothes dryer because each battery doesn't have to deliver as many amps. The amp-hours a battery can deliver at light loads is a lot more than what it can do at heavy loads. So with the additional 12 batteries I figured that at 1.5 kW nominal load each battery only has to deliver 3.5 amps to the inverters. At that amp draw the 36 batteries will supply 1.5 kW nominal for about two days and still be above 50% SOC. I NEVER draw my batteries below 50%. If the loaded voltage drops below 24 for more than two hours, the inverters bring the gen online.
So my thoughts were that by adding the extra batteries that it won't work the bank as hard, won't as deeply discharge them, and they'll last longer.
--
Chris