Some thoughts about my system. I have implemented PV and batteries at our house. We also have a Nibe ground source heat pump (S1255-12) and a separate Nibe hot water boiler. We also have an EV car. Before I acquired batteries I was heating the Nibe boiler (200l, 2-phase, one resistor) with surplus PV power. I used a Carlo Gavazzi proportional control SSR (RM1E48V25) which is controlled by Ouman AXL programmable controller. I have configured a PID controller in Ouman which provides 0-10VDC voltage for the SSR. OH has a PID controller and there is a link for additional hardware, though.
When I acquired batteries I don’t bother to use the PID controller any more to heat the hot water boiler. I’m using Alfen charger for my EV car. This charger has Modbus TCP but I haven’t found a good way for controlling the charging current so I charge the car during winter time using cheap hours or during summer time I use surplus PV. I sometimes charge the car from the batteries.
Batteries are not that expensive nowadays. I have 3x15.4kWh batteries from Basengreen and a 3-phase Deye 12kW hybrid inverter which you can get easily from a reseller in Europe.
So, nowadays I don’t care that much about optimizing the hot water boiler and charging of my EV car when I get enough PV power. In addition, I can run the heat pump normally so I don’t need to “overheat” the house e.g. during cheap hours at night. dk8pn discussed above the efficiencies but I’m not that worried about this because PV power is free.
I can say that I’m very happy with my PV panels and batteries.