That is cool, I was hoping to do something similar at smaller scale since the net metering is ending soon in NL. I did not fully understand the specs of your installation. You have 3,5KWh of solar? you mean 3,5KW? You forecast your consumption to be 4,5KW? You mean 4,5KWh per day? And then the 400W continued during the night (sounds quite a lot for the hours when everybody is sleeping).
How do you regulate what you use from the batteries and what you send to the grid? (Specially when referring to different consumption levels between day and night?) I only know of inverters that can be regulated at a constant discharge rate analogically; can yours match real time consumption?
Also curious about knowing if you made this project for fun or because you do see a payback as the net metering disappears in NL.