Newbee at solar..

Batteries that are listed for float service, often do not have a very long cycle life (UPS batteries are frequently replaced every 2 years, or after a deep cycle or two).

Do you have a link to a website/product description that talks about cycle life vs cycle depth?

In general, I am not a big fan of placing a bunch of 12 volt batteries in parallel (8x 200 AH = 1,600 AH @ 12 volts).

For a 1,600 AH 12 volt deep cycle flooded cell lead acid battery, I would suggest that such a bank would be good for about a maximum of 4,000 Watt AC inverter. For AGM, you might be able to get 10,000 watts from AGM batteries, but your wiring would have to be pretty hefty:

• 10,000 Watts * 1/0.85 ac inverter eff * 1/10.5 volts cutoff * 1.25 NEC derating from wiring+breaker = ~1,401 Amps "branch circuit"
  

That is some very heavy copper bus bars (or multiple heavy cables).

Realistically, for a 12 volt battery bank, ~1,200 to 2,000 Watts would be more practical:

• 1,200 Watts * 1/0.85 inverter eff * 1/10.5 volts * 1.25 NEC derating = 168 Amps rated "branch circuit" recommended max current design for 12 volts
  
• 2,000 Watts * 1/0.85 inverter eff * 1/10.5 volts * 1.25 NEC derating = 280 Amps rated "branch circuit" recommended do not exceed for 12 volts
  

If you look around, that is already some very heavy cable (that you have to keep very short to keep voltage drop low, and you should have fuses/circuit beakers installed to prevent short circuit fires).

Nominally, a 10 kWatt AC inverter would be 48 volts or ~1/4th current of a 12 volt system--I.e., 350 amp NEC branch circuit... Still a  lot of current, but not 1,400 amps worth. Plus, instead of 0.5 to 1 volt wiring drop, you have closer to 2-4 volts of allowable voltage drop for a 48 volt battery bus system. Bad side, 350 Amps @ 48 volts DC is a darn nice arc welder. 12 volts is just on the edge of "supporting" a steady arc.

For an emergency backup system... It is hard to beat a genset that runs from natural gas or propane. Or diesel or gasoline (with fuel preservatives) to manage the heavy loads. And, a small (say 300 watt AC inverter) solar power system to give you lights at night, cell phone charging, and laptop computer access.

Building a large solar power system for purely backup usually does not make much economic sense (solar power still costs you money even if you do not use it--Batteries typically last ~5-8 years, electronics around 10+ years).

Tell us a bit more about what you would like to do... Perhaps we can help point you to something that will work well for your needs.

-Bill