Here is a link to lots of free battery and solar information. A good understanding of off grid systems saves lots of money in wasted batteries, etc.
http://www.windsun.com/Library_Index.htm
Another fine site, whether you're mobile (boat or RV) or fixed (house or hole in the ground ;)):
www.amplepower.com
What these people don't know about 12V power systems probably isn't worth bothering about.
I started with 12 volts but as I got to wanting more and more power I found that 24 or 48 volts was more efficient. For a 4000 watt inverter the input cables have to carry 333 amps at 12 volts, 166 at 24 volts and 84 at 48 volts. The cable from the batteries to the inverter and between batteries get very large. I am at 24 volts because my wind generator is 24 volts. 12 did work great when I had a small system though. 12 volt solar panels can be series, parallel or series/parallel wired as necessary for any of the systems as can 6 or 12 volt batteries. The 24 volt wind generator is stuck at 24 volts.
The ample power people know about higher voltages too! ;)
Even cars are starting to use higher voltage systems. I think I read that BMW is starting to use/standardize on 32V.
Dijano that the fastest rated Pentium 4 chip uses an astonishing 119 AMPS @ 12V at full power - just for the CPU? ;)