I'm going to diverge from the group here and say the adding parallel strings of batteries is not a great idea. For a lead acid battery to live a long healthy life, you should try to not pull it down below 80% capacity and then charge it back as fast as you can when you can. So basically you only get to use 20 percent of your battery. Now most of us probably run down to 70 percent and 60 percent on bad days just because the convenience of electricity outweighs the harm we know we are doing to the battery bank.
If you add parallel strings of batteries in order to obtain higher capacity, you run the risk of of not being able to charge the bank back up at all. Without a larger solar array, you could get into a pickle one day of needing to pull out 50 percent of your battery bank and a month of good sun cannot get your bank back above 70 with charging your batteries plus your daily load. A perpetual state of under charged batteries is really hard on their life.
To correct this you need more panels. Then you end up with so many panels that on good days, your batteries are charged by 11am and your making so much power that you cant use it.
There are really only two solutions to this. If you want to be off grid, you must have a generator. This has maintenance costs and is expensive to run, and I'm going to say it, they will put out far more pollution then burning coal at a power plant to produce the same amount of power.
The other better option is grid tie. I've been off grid for 8 years and have sworn that the electric company is evil etc etc. I have changed my opinion on this 180 degrees and now I believe that the ONLY option to have the most efficient solar system is to be grid tied with battery backup. For a small monthly fee/ service charge. Mine is 27.50 usd and is pretty high around here, you are basically renting a battery of INFINITE capacity, NEVER goes bad and has ZERO maintenance issues, and very minimal losses. When you batteries are charged at 11am, instead of you panels putting out zero electricity, you get to charge the grid at full capacity.
There is a point where batteries simply cannot accept any more electricity as they get up to 80 and 90 percent charged. You may have an 80 amp solar charger and 2000 watts worth of panels, but when your batteries can't physically take more the 15 amps in full sun it's almost sickening and extremely wasteful. Grid tie fixes this and increases the efficiency of the system 10 fold. WITH GRID TIE YOU CAN ALWAYS CHARGE 100 PERCENT OF THE SOLAR PANELS CAPACITY! That's a huge statement that should be yelled from roof tops!
Do not hesitate to get grid power !
This less then ideal charge profile of batteries where they wont accept much as they become fully charged is really bad for generator run time as well. It's a horrible feeling to have your batteries refuse to take anymore amps as they approach fully charged. You can watch the battery gauge accept 400 watts for 2 hours while your 3000 watt generator is wasting fuel.
If your hooked to the grid and you need your battery bank charged, something that may cost you 2 dollars of fuel in a generator will cost you cents in grid power. For example, I ran a bank of 4 batteries of 1200 watts each for a long time. If you pull them down 1200 watts, your at 75 percent to charge this up with a generator is about a half a gallon of gasoline for me. Right now that's about 1 dollar. But there are hidden costs with the generator, oil changes, spark plugs, fuel and air filters, the time servicing etc.
To purchase the 1200 watts I need to go from 75 to 100 percent from the grid costs me about 12 cents, with no maintenance costs and if I stored that power in the infinite battery that is the grid, it could potentially be free!
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