John61CT said:
So start small on the bank, big on the panels, see how you go on those goals, then expand the bank later to give yourself a cushion.
It is much better to not have to add new batteries to older ones. Old and new in parallel quickly weakens new to state of old. Better, imo, to add more solar Mid battery life. How detrimental adding new to old is to the new batteries, varies.
Health of the old battery is the big variable when doing this.
If a bank is relatively new and has under ~40 deep cycles and proves insufficient capacity wise when proper recharging was mostly attempted and achieved, then adding New to old can work much better together. But , the Old batteries should be given a full charge( extended absorption), then an equalizing/reconditioning charge (few hours at 15.5to 16V) and allowed to rest before being put in parallel with the new ones. If all New and old Resting full charge voltages are within 0.02v, they should be good to be put permanently in parallel. If they are 0.05v or more apart they will not be as happy. If the new rest 0.1v higher than old, they will be unhappy.
Brand new batteries usually need a deep cycle or two before they will read their normal fully charged resting voltages.
I'd suggest milking initial unsufficient battery bank until death, spend money to increase solar, or alternator contribution with thicker shorter copper, then after battery failure, expand capacity with all new house batteries, and perhaps charging sources too.
If a New pair of 6v in series can't run your microwave except when absolutley fully charged, then you will likely need a second set, so it would be wise to plan enough space for 4, but see if two is sufficient and if not, then add 2 more quickly.
Ideal, need not be achieved, but one should be aware of what is downright detrimental and try and avoid committing premature batterycide. The problem is that the process of committing batterycide is not obvious to most Newbs, until that day when 'just fine', no longer is.
That day can certainly come too soon and be too expensive. if when it does, the Newb either replaces batteries and upgrades charging sources, or resigns their next set of batteries to a similar death.
The other option is using less electricity by being more efficient and living without. It is certainly less costly to conserve, than it is to expand and complicate, to generate enough juice, that one has no concerns.
But solar is kind of addictive too.
So if one is going to go crazy on Solar wattage, or battery capacity, I say more solar wattage.
