I have a 12.8kw PV array and 81kwh battery bank in an off-grid configuration - and nearing 3 years of operation - so I have good solid numbers as follows:.
*The array produces 18,000kwh/year or 49kwh/day. I get 15,000kwh/year of usable power - e.g. 83% overall efficiency and 41kwh/day. Note: I have AIMS ETL inverters and this is the biggest loss of efficiency in my system.
*Spring/summer I get 2000kwh/month of useable power
* Winter is 500kwh/month - about 25% of summer.
* My average consumption is 3000watts/hour over 5,000hrs per year. This is an average of 13.7hrs/day @ 3000w = 41kwh/day of solar power.
* My average DOD on my 81kwh battery bank is 40%.
By extrapolation, to get 13kwh/day (on average) of useable power at 80% DOD you'll need at least 32% of what I'm running which is:
1) 4.1kw PV array
2) 13kwh battery
If you want this thru winter - e.g. 13kwh/day, you'll need
1) 10.3kw PV array
2) 33kwh battery
but of course you'll have 39kwh to 50kwh/day in summer - e.g. significant excess over 13kwh in winter.
13kwh/day * 3 days = 39kwh/day of useable battery. At 80% DOD that's 50kwh of battery. 48v@2000ah = 96kwh of battery - e.g. more like 13 * 6 days.
20 * 450w = 9kw PV array. My estimate is 10.3kw - so this is in the ball park.
Suggest PVwatts
https://pvwatts.nrel.gov/ web site as a way to compare your area to my numbers for adjustments.
If you run PVwatts for your location on 9kw PV array you can get a percent of 18,000kwh/year that I get and adjust from my numbers and be pretty close. Here's the breakdown of how my numbers add up to 18,000kwh/year of PV production.
View attachment 65455
**Best advice: If you can - start at your 20 (or whatever you decide) panels but try to leave room for more - more panels, more charge controllers / inverters, more wiring, more batteries, more everything for future expansion. Once you get a system running - its SOOOOO COOOOL - you may very well want to expand it. That's what I did. Started with 24 panels and 30kwh of battery and expanded to 45panels and 81kwh of battery