Gas off from Batteries for PV

[beckhamk]

We are seriously considering looking into a PV system. I udnerstand that the wet batteries give off gases which need to be vented. I wanted to know if the sealed/AMG/gel batteries also give off gasses or not?

Also does anyone have any sites they can point me to to better understand  typical usages and whats required.  I am really trying to figure out  the amp hours for batteries.  For example you  can get 100 amp hour battery which can draw 5 amps for 20 hours or 20 amps for 5 hours.  But thats for one battery, how does this change when you have a bank of batteries (i understand there is a difference for series vs parrallel). Just trying to determine how this all fits together.


Thanks in advance!

[MountainDon]

AGM do not off gas when used correctly. Over charging or at too high a rate might cause that.  AGM's sound great but IMO have a huge drawback. You can not use a hydrometer to obtain the specific gravity which is the best indicator of the state of charge.

In series you add up the volts and the amp hour rating for the series string is the same as for a single battery.

In parallel the voltage stays the same but the capacity (amp-hours0 of the parallel string is added up.

Google "battery FAQ" and you should find the faq section at Northern Arizona Wind-Sun. Great resource.

[Native_NM]

AGM batteries do not gas, and can be used indoors.  They typically cost twice as much than wet batteries.

There are dozens of websites on estimating usage and need.  Amp hours for batteries are pretty simple - the amps a given battery can deliver at a given voltage and discharge rate before it is dead.  Most people use half the rated amp-hours as the useful capacity to ensure that the battery DoD (depth-of-discharge) does not fall below 50%.  This ensures the longest battery life. 

Batteries are wired in banks in either serial or parallel, but usually both for solar.  Most batteries are 12V.  The most efficient solar banks are 24V or 48V.  Residential power is 120, or 10 times 12V.  A 48V bank is only 2.5 times the bank's voltage, which means much lower amp draw, smaller wire, and cheaper install.

If you wire (4) 100 AH, 12V batteries in parallel, you will have 400 amp-hours at 12V.  If you wire them in series, you have 100 amp hours at 48V.  You can wire them in series and parallel, and have 200AH at 24V.  Nothing changes in terms of the total energy available.

[rick91351]

Have you gleaned anything from the forum's tread OFF GRID POWER; various thoughts on...   

http://countryplans.com/smf/index.php?topic=6059.0