I live off-grid in Southern Arizona (~30 miles South of Tucson airport and ~40 miles East.) I originally setup a ~4kW array (panel specs) and saw peak production hit about 3.3kW (partially due to my choice in CC - Schneider MPPT-60-150 and having the panels setup in a 4 strings of 3 panels in series - 3S4P to a Midnight Solar combiner box.) I went all-in w/Schneider as you can see by my signature. With this setup, I could produce over 26kWh a day in sunny conditions (it could have actually produced more, but the CC went into float mode by 3PM and most days by 12PM, so solar input was limited to what we could consume after the batteries were full.)
We noticed during Monsoon season (rainy season - yes we get rain in AZ) that we could not power everything we wanted: 2x air conditioners, power tools, household appliances (fridge, freezer, etc.) with that single array and keep our batteries full due to cloud cover and 100+F temperatures. We added a second array (~3.7kW - panel specs again) and now produce 6.5kW and over 43kWh/day peak (when batteries went low) with most days topping out ~35kWh (this was Aug 2020 during Monsoon season.) We now produce more PV power than we (currently) need. We are getting ready to start building our permanent residence, but I have calculated our future usage and I think this configuration will suit our needs as far as PV input is concerned. If you find you are hitting the full mark for your batteries before you run out of sun, best to invest in more batteries.
We currently have used BYD 25.2V/220Ah nominal batteries (8 modules.) I can push them to produce ~25kWh as needed. This is the area we've invested most in and have just purchased 64 new 272Ah cells to build a 55kWh battery that should be able to fulfill our current needs (we use a lot of electricity for just about everything currently: cooking, heat, refrigeration, tools.) It can get down to the 20's F here in the high desert of AZ overnight. I should mention our configuration is 48V - for peak loads like 6kW, that means your 24V system will need to push 250A. You'll need to size the cables/bus bars appropriately to handle that. This is why I went 48V. My system is sized for 250A peak as my inverter can sustain 12kW for 60 seconds.
I'm curious when you say you need 6kW of house usage? Is that peak, cumulative, average, mean? What I did initially was to create a spreadsheet of all the electrical appliances we use with their wattage and a rough guess at how many hours a day we'd need to use them. This gave me a good guess at kWh usage. That's how I originally sized all of my components. Unfortunately for us, I didn't calculate in enough time to live comfortably without sufficient PV input during extreme temperature swings (hot and cold - hence the 2nd array) and system maintenance/upgrades (we do have 3 generators - the largest being a Generac XC8000E for backup/emergencies.) Another consideration I missed was how much usage I'd need during night time hours. When you consider this figure, do one for Summer and one for Winter. Do you need air conditioning during summer nights and/or heat during winter nights? This will help you decide on your inverter size (sustained/peak) and battery storage needs.
Of the three components, plan the majority of your budget to go towards batteries (unless you plan to exercise a generator to take up the slack.) Depending on your DIY'er skills, you could pick up used cells/packs and build your batteries. If used cells are the path you want to follow, a good BMS is a must. For my new batteries, I'm 99% sure I'll be purchasing an Orion Jr. 2 BMS, as it has basic support for Schneider and can control multiple relays - again, planning for peak loads of 250A and I don't want to rely on the BMS for that kind of throughput. I actually used this forum to get in on Group-buy pricing for my new cells ~$86 per cell. Since I'll have a significant amount of the system cost invested in these cells, I didn't want to skimp on the BMS/critical path configuration. It didn't make sense to spend $5,500 on a battery and use a BMS that costs less than $100 - that works out to be less than 2% of the cost for what I like to call battery insurance.
In that aforementioned spreadsheet, I setup tabs for Inverters/CC cost/efficiency/capacity analysis, panel data, wire calculations, panel mount configurations/costs, equipment installation layout, overnight calcs and BMS options/costs. I analyzed things down to the cost/watt with inverter efficiency baked in as well as cost/wH for batteries using rated capacity and real/guess capacities (100/80%) to help narrow the field.
I can share the spread sheet if anyone would like. It's in a Google Sheets doc, so I can share if you have a Google account.
I think I've rambled on enough and I know others will have some good input on this topic as well.
