the math is easy enough to figure out, a lot of people gave you some
good information on this thread. for my own deep cycle systems i've
noticed it never works out like the math says it should though, never,
not in actual practice. you kind of imagine all these perfect numbers,
12 volts and 100 amp hours and that means you can do this task for
such-and-such a time and it'll take your solar cell such-and-such time
to recharge and all this. and there are even charts that give you an
idea of the danger areas for depth of discharge, that is, discharging
the batteries too much and too often, and how many times you can go to
certain levels before you have to get new batteries, etc. my
experience has been that in the end the math is ok for like a really
general idea, but that's about it. the math quickly turns into
non-sense in the face of harsh reality. in actual practice your
battery bank is always in some weird state of charge that's hard to
measure because it varies so much with temperature, battery age, what
angle the batteries are sitting at, how much water you put in it last
time you serviced them, etc. and who knows what your solar panels are
doing depending on time of day, cloud cover, etc, and the same for your
wind generator, and even your alternator, none of it has very much to
do with what it's rated at, or what the specifications claim it's going
to do. then your loads are so variable too, which lights will you have
on at which times ? how often is the compressor going to flip on in
your refrigerator ? how many amps is your starter going to draw ?
does humidity affect any of it ? etc. in reality it's a crap shoot,
and nobody really has any idea what their system is doing most of the
time, and it's even hard to measure the voltage on the batteries
because power is going into them from the solar panels and things most
of the time, even on shady days. and even if you could measure the
battery banks voltage it doesn't give a real measure of the state of
charge. so you design it the best you can, fit in as many batteries as
you have space for, try to minimize how much power you are wasting, try
to keep everything maintained (especially your batteries), try to put
in as much power generation (solar and wind) as you can, then cross
your fingers and hope for the best. i mean, really, does anyone really
have any idea how many amp hours are in their battery bank right now ?
lol. yes, yes, i know, your battery power meter tells the whole truth
G. my personal experience has been that it's a bunch of voodoo.