I am offgrid these days (on a 'temporary' system at the shed that runs the shed and my caravan, while building the house) that supplies 100% of my power here- only 1.5kw of panels (3 250w facing north, and 3 250w facing west), charging the 20kwh lithium (LYP) battery bank that feeds the 12v lighting circuits, the 12v tv (inbuilt lol) in the van and the 12v water pumps for the sink and the shower in the van on-suite, there's also an rather elderly 8kw 12v inverter (I bought it back in 2014 or so, to fit to my ute lol)- this system allows me about 7-8kwh a day in spring and autumn, a fraction less in summer and in winter drops to about 5-6kwh per day... (the summer heat kills the panels outputs by anything up to 20-25% when the summer air temps are over 40C lol- just when running the aircon hits the hardest)I think we can get 4 panels on each side for 12 total and with a largeish battery should be enough for for our fairly low usage except in the dead of winter and with the octopus flex tarrif we will buy at cheap rate to top up in winter. Long term it is certainly a wise move but we need to find the right system.
Helpful hints- avoid L/A (lead/acid- ie gel/flooded/AGM) batteries- go for the lithiums (LFP (LiFePO4) are ok, cost about twice as much as L/A but last MUCH longer and have more usable Ah of storage than L/A with the same 'label' Ah) LYP (LiFeYPO4) are slightly more expensive than LFP, but have a much wider temperate range than LFP- with L/A and LFP needing to taper off their charge rate when the battery temp goes higher than 40C, where the LYP can still charge at its full rate up above 60C and doesn't start to temperature taper until it hits a battery temp of 80C!!!! (important when we get temps over 40C for weeks on end here in summer) (they also work better than L/A or LFP in sub zero temps)
Batts- don't be fooled by the 'label' Amphours rating...
You won't get it!!!
L/A should really never be taken below 50% DOD (depth of discharge) on a regular basis, or their life expectancy will be very short indeed- at 50% DOD a L/A will have around 3-5 years life expectancy before needing replacement, where you reduce that to 25% DOD and you are looking about 5-7 years, at 10% DOD its 8-10 years- but that means you are only capable of using 10% of your storage capacity (eg a 100Ah battery, only using it as a '10Ah' one
Lithiums (dont use li-ion/LiPO) like LFP cost about twice as much per 'label Ah' as L/A, and LYP about 2.5 times what L/A does, but you can get 13-15 years at 80% DOD, and 18-20 years at 70% DOD- making them much better long term value that L/A or Li-ion ones
Use only MPPT charge controllers (and the higher the PV input voltage the better), mine are 150v PVmax rated for a battery bank between 12-48v- the battery bank voltage will set the total array wattage they can handle
(in my case, they are 60A each, at 12v they can handle 750w per controller, 1.5kw at 24v or 3k at 48v)
12v nominal x 60A means 13.8v charge voltage 13.8v x 60A = 828W, the manufacturer derates it by 10%, making its 'rated limit' 745.2w- they say 750w is good lol