I’m trying to write this description as clear as possible, for 2 hours now. English is not my mother language, apologies in advance.
So, it started about 1 month ago, when I commissioned (apparently wrongly) my solar system.
It consists in 36 bifacial panels of 440w each, connected to a MPPT 450/200.
This MTTP puts the energy in a lynx bus bar distributor with a smart NG BMS 1000 and a Class-T power-in, where I have 4x 25,6V 200Ah NG batteries each in a 2s2p configuration.
In this distributor I have also 3 Multi 5000/48 connected and configured in a 3 phase system. The Victron EVCS is in the AC_OUT of one of the multis. All my loads are in the critical loads outputs.
The panels do an amazing job charging half capacity in less than 2 hours of full sun.
I had since the beginning, the grid input circuit breakers off, except for a moment or another, where I turned the change over switch and fed my home from the grid input to try to change the programming in the multis, and one other occasion I’ll describe in a moment.
In the last 30 days (yesterday’s stats) I consumed 632kWh, from which 21kWh came from the grid.
In reality, my consumption is much lower. It’s this high because I use home assistant to keep some electric heaters plugs on, when the batteries are above 95% saving some gas heating in the process.
The big majority of this grid consumption was in a certain day, that I woke up to a cold, dark house. I went to the garage where I had the multis blinking red lights pointing to low battery.
I went on the main board, turned the change over to the grid and left it so until the end of the day when I came back from work.
When arrived in the end of the day, the sun did his trick and I had a full battery, like it happens almost every single day.
I could later see in my home assistant history that the inverters stopped exactly at 19.6% SOC.
After this episode, I installed the ESS assistant in hope to improve something, but later I read it shouldn’t be used in an off grid situation.
So today I gave another shot in the programming of the multis, I reset everything, removed the ESS assistant, and made a basic 3 phase programming.
I noticed the loads were being fed from the grid, instead from the 100% charged battery and the MPPT was not outputting anything. I turned the grid input circuit breakers off and the loads started being fed from the MPPT.
After some back and forth I thought, let me go read again, but after a few hours in the community forums and google I couldn’t find a pointer on what to do.
In my understanding I can’t use ESS because basically I don’t want to inject energy in the grid; the price they pay for the injected energy is peanuts, I prefer to save the batteries cycles.
I came to the conclusion that I use slight less than 50% SOC/24h, 20% between sunset and sunrise if the car is not charging. I don’t need to charge my car every day, it can hold 2 or 3 days if needed or as low as 3 or 4 kWh per day to reach the weekend when it can be left plugged in auto for 2 days.
So, what is my objective? Use all the solar I can, and when the batteries go too low, the grid comes in and supplements the batteries.
Basically I want my loads to be fed from the batteries and MPPT, letting the grid take over if SOC gets as low as 10% and letting the sun do his job the next morning. When the battery reaches a point above 40% the grid should be disconnected again and the loads being transferred back to the batteries. After maybe 5 days without reaching 100%, use the grid to charge the batteries, during the evening at a cheaper rate.
Is this achievable?