24V system alterations/questions

I see perhaps more solar panels to charge the batteries, but honestly if its working now and you are really replacing soon, might not be worth the effort.

I am putting together my first system and I seem to have come up with numbers similar to what you have, and the difference I have is that for 24 Volts whit 400 ah batteries, I wanted 1200 Watts of power, but it seems you have a generator set to come on automatically, which I don't that may make up for it.

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This is what I'm basing my system off:

At 12 Volts and 400 AH I would have 600 watts of panels and a 1000 watt inverter being able to power my setup with the expectations of watching TV and running some LED lights all day, and possibly brewing a single cup coffee maker
If I expand to 24 Volts and 400 AH, I would have 1200 watts of panels and a 2000 watt inverter with the expectations being the same except I would be able to use a 1700 watt electric kettle to boil a cup or two of water.

I don't know the particulars of the forklift, but I think running a generator for hours to charge a forklift battery is a bit much, and seems that battery matches what you are putting out for the solar output you're making now, so I'm wondering if a propane forklift may be better. I'd use about 4 gallons of gas which is one or two refills of my generator for 8 hours of charging.

The biggest problem I see it that using a PWM type CC you are turning that 640 watt system into maybe a 425 watt system. That is way too little to properly recharge your battery system which is probably why you are using your generator so much.

As your batteries are at 5 years old, in parallel and have been under charged/ run low, I think you will find they are in very poor health. Test them with a hydrometer to give an idea of where they are at.

Then depending on the generator Voltage set point you may be able do an equalize charge or at least an extended bulk charge, which will tell you via your hydrometer how good/bad they are. You would need to monitor battery temp during this charge as if there is a bad cell it may cause issues. You may also be able to do one bank at a time.

I would just make sure the panels are clean, not shaded, check all connections and charge and test the batteries. I would not be putting any real money into the system. With the KWH you are using and the set up of the system I would put any cash toward a new bigger system.

You may be correct. The description of "2 banks of 12 2V - 400Ah" equaling a 24V system sounds like there are 24 2V batteries (2 sets of 12 wired in parallel). But if each 2V battery is rated 400Ah then his system is an 800Ah and the OP has way to little panel wattage or proper charging to keep it happy. Especially after 5 years.

Sorry should have been more clear on the batteries. Yes they are 12s2p 2V batteries. It's an old forklift battery with the 24 batteries in one container.
I just double checked the label and it actually states 511Ah and I believe it was originally a 48V battery as it looks like one of the interconnects has been cut to make two 24V batteries which are then wired in parallel...
On a full charge I get roughly 300Ah at 24V out of the battery set-up before the generator kicks in. So probably fair to assume the battery is pretty stuffed.
One set of batteries also seems to be doing the majority of the work, on a 4A load one set of 12 batteries is supplying more than 3A and the other less than 1A.

I may consider testing each battery, finding the reasonable ones and making one 24V battery from the best of the 24 batteries available.

Well if it was once a 48V 511Ah system but now it is a 24V 1022Ah system. So you need about 100Amps to properly charge it. That sounds like you will need 2 60amp chargers if you go with solar. That will require a much bigger panel wattage then that 640w system you have

The uneven discharge worries me a little. I am not sure how but there is a resistance difference between the 2 parallel systems. That will cause an early failure in the system doing the most work.

Is there any issue in using a common negative and a common positive charge controller together on the one system?
An older epever tracer which is common positive has come up cheap whereas a newer charge controller I also plan on using together is common negative.