However, it is my understanding that for the purpose of keeping the cells equal, a single series string is even better than two parallel strings. The guy I talked with even recommended splitting my bank once in a while and equalizing the series strings separately.
I have to agree with ClockMan on part of this... Two parts to it:
1 - GASP! There's no way a single string has better balancing behavior than parallel strings. When a cell gets slightly off balance, a single string keeps the
entire load passing through that weak cell. With parallel strings, the weak string still
contributes to the load without having to support the entire drain. Higher discharge rates exacerbate weakened cells, as do higher charging rates; the reverse also happens as well. A weakened cell will reach full before the others, and at higher currents, this will happen faster and faster, straining not only itself, but preventing the remaining cells in the chain from reaching full charge (or at least boiling itself to death during the process).
2 - On the other hand, I agree with you that breaking strings down into smaller chunks for equalization
can be beneficial. It also will help you isolate any weakened cells so that you can get rid of them.
On a
third, surrogate hand, having multiple (parallel) strings will allow you to disconnect one string at a time for things like maintenance, troubleshooting, individual equalization etc
without power interruptions at the output of the inverter (for example) in the process.
This will play more of a role as the size of the system increases. Large banks are expensive, but can be more expensive to keep replacing if they aren't designed right. Gotta do the homework for sure.
Size of system and the like, I cannot comment really on which is best, although I'd shy completely away from 12V (others will strongly disagree, thats fine) for powering an entire building. Just the copper costs alone can offset what you might save on things like inverters.
I
have done some looking into the idea, as I intend to be completely off grid one day, and the conclusion I came to is that my system will be a 48V deal. Currently, I'm learning on a 12V system, and also have a 24V system (that is not RE powered) for backing up my servers. That system was 12 originally; had to upgrade it to keep up with the demands of the load. Luckily it was small enough at the time, it didn't cost me that much to do so. I can
easily imagine that I would NOT want to have a sizeable 24V system and have to upgrade to 48. That could get very expensive very quickly (in terms of overall cost).
Everyone's needs are different. And as pointed out, availability in your location for a given price plays a role as well.
My $0.02
Steve