Wire Size For Interconnect Cables in 24V Battery Bank

[joeyp]

Joey, a C8 discharge rate on that battery bank at 24V is only 700 watts. If you try to suck much more than that out of them you'll get voltage sag at the inverter (regardless of cable size) and eventually the inverter will shut down due to low input voltage. You can probably run 1000 watt loads for short periods of time (like maybe a circular saw to cut a couple of boards) but don't expect to be able to run a 1500W space heater.
When I was putting mine together, I compiled a binder with over 200 pages of electrical code and studies. I found the Sandusky labs PV power systems report to be very good reading and I incorperated all the labeling from it into my system. You're going to have to get into the code for PV disconnect requirements, fusing, breakers, labeling etc. It's no small task to figure it out without any help.

What effect would creating another string (exactly the same) and connecting it in parallel have, aside from the obvious of doubling the capacity? Would that allow a higher draw without as much voltage drop?

[thastinger]

Yes, in theory that would give you 1350 watts at a C8 discharge rate. The problem becomes the life expectancy of parallel battery strings and all the problems that come with that.
If 2000W is really your desired output than you should consider a larger Ah capacity 24V battery configuration in a single string or go to a 48V battery bank buy buying 4 more 105REs like you have now.
The system in my sig has been working well for me for a bit over a year now with the 8 T-605s in series to make a 48V 210Ah bank.
If you're dead set on 24V then you might look into the L16 style battery at 370Ah each. I believe the 105REs you have are 225Ah.
To figure the C8 discharge watts just divide the Ah capacity of the battery bank by 8, then multiply that by the battery voltage then multiply that by the efficiency rating of the inverter (i.e 92% becomes .92).
All this is based on the 20hr rate, the Ah rating is higher for the shorter hr times but the capacity will go down the harder they are drawn on.
Just think of it in pounds of energy storage potential, double the poundage from the 4 you have now and roughly double your capacity out the inverter, you can configure the weight in several ways (i.e. 4S2P give you 24V 500Ah or 8S gives you 48V 225Ah) but the weight is the same, and the weight is what matters.