I was looking back at reddit posts (while deleting them), and I realized I’d written a book worth of stuff about this topic. I would write it all again, if it is helpful. But for a brief synopsis of “how it works”, here is what one does:
Assess power needs - look at your living standard and catalog all the devices you power, and estimate the time they operate - power is measured in watts, and time in hours. Multiply to get watt-hours; then divide by 1000 to get kilowatt hours. Compare with your utility bill.
I strongly recommend to have a look on this website:
https://re.jrc.ec.europa.eu/pvg_tools/en/tools.html#SA
You can input your location, your daily consumption, your battery capacity and the amount of panels you have.
From that the website will use a database including the weather in your area and the mountains around you to generate a report that tells statistically you how many days per month your batteries will be empty.
It’s taking into account the fact that you can have several days with no sun, the fact the in winter the sun might set behind a specific mountain …
Excellent; this seems to show my system has a high reliability, as I have observed, and at the most severe conditions, about 10% or 15% reserve capacity. I expect to have an EV later this decade, and my existing house system will not provide for that. I may need a stand-alone system for EV charging, or some EVs have their own charging (Aptera looks attractive, there may be others?) I haven’t figured it out yet.