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Or why not use DC for the entire data center and put the battery at the Data Center level?

12VDC, each unit needs 300W at least... That's 25 amps per unit. Think wire gauge. That's the reason, long and short. That, and you can't run 12VDC very far before power loss becomes a significant consideration.

Tesla figured this out over a hundred years ago -- AC powers and transformers = more efficient.

Since becoming a ham several months ago, I started learning all about batteries and 12V power and while I was at some solar energy stuff. Starting with a shed project is a great idea. I am assuming you are looking to light things, not run a planer.

• All electrical should be 12V dc if you don't have to run 120V AC for anything. (no conversions!! yeah!)
• Use a good quality deep cycle or marine battery. Car batteries are intended to give lots of amps for a short period of time.
• You will need a charger manager that can reduce the charge to nothing from the solar panels so you don't boil you battery. Well, just go to Battery University and learn all about batteries.
• http://www.batteryuniversity.com/
• Look at using 12volt lights
• 12v side of life: http://www.ccis.com/home/mnemeth/12volt/12volt.htm
• Battery FAQ http://www.windsun.com/Batteries/Battery_FAQ.htm
• 12v CFL http://www.unlimited-power.co.uk/low-voltage-lights-12v-dc-CFL.html
• Very good inverters from Astron http://www.astroncorp.com/dc2ac.shtml with modified sine, not square sine if you want to run more than just lights.

Oh yeah, treat all large batteries like they are bombs ready to go off. Store them outside, and if it gets below 0C then you might have to figure out how to keep them warm. Good luck with that.

From the link:
"a deep-cycle battery is designed to discharge down to as much as 80% of its charge capacity"

80% is not "almost completely".

I may be wrong but I think that it should be it can be discharged up to 80%, in other words until it only hold 20% of it's charge. I think this page does it better:

Deep cycle batteries are designed to be discharged down as much as 80% time after time, and have much thicker plates.

if you actually had any experience with deep cycle batteries, you'd know that discharging past 50% drastically reduces the lifespan

"A good quality deep cycle lead acid battery will cost between $50 and $200 and, if properly maintained, will give you at least 150 deep discharge cycles."

"All the articles I read on battery usage recommended that lead-acid batteries not be discharged to a point where less than 20% of capacity remains."

I've got one for my backup server, it cost me like $300 at a boat accessories store. 89 AH and it runs for hours (something like 10 on a fairly power hungry old skool Athlon TBird, or something to the effect - might be a duron, come to think of it). Oh, and watch out for thermal runaway during charging, or you won't have to light a smoke to be toasted.

More Info:
Deep Cycle Battery FAQ

Depends on your current draw. Check out this table. Remember that by time you wire your entire house, there will be several hundred feet of wire.

There's a reason we feed houses with AC.

Solar Insolation Maps

Avg. solar radiation is surprisingly uniform. Sure, the southwest is higher, but it's at most 2x anywhere else in the U.S.

Bringing the information to a thread more specific to the subject, i'd like to inform that #7806067 previously posted a link to a interesting Battery FAQ

Along with CPU power consumption, review hdparm configuration of ATA power management and spindown of the hard drive, e.g. IBM/Hitachi drives.

A shorter drive duty cycle reduces power consumption of both drive and cooling fan. With bios support, boot from ATA compact flash into a tmpfs filesystem for shortest OS-attributed duty cycle of mechanical parts. Or shrink the mechanics, circa IBM Microdrive or iPod-scale 1.8" drive.

External deep-cycle batteries must be power regulated, fused, sealed AGM or safely boxed and externally vented to remove discharged hydrogen.