For this pet project, I would like to know if MPPT was working. In addition, collecting more data seems worthwise later on. The sensors to measure current and voltage are varied. One of popular line is TI INA219. INA219 is capable of measure upto 3.2A and 26V. It is a single channel sensor. To to measure solar charger, we need two INA219, one before and one after the charger. Another option is using TI INA3221 with 3 channels. Most PCB board is available with a shared input voltage, and thus is suitable for measuring power consumption upto 3 clients with the same power source. For solar system, we have at least 3 levels of voltage, so that we need to modify the PCB board. Simply cut the PCB trace connecting to the shunt resistor and solder a wire for the input. By this modification, CH1 (channel 1) measures current and voltage of the panel, CH2 measures the voltage and current to the battery and third one can be used to measure power consumption of other clients.
and here is how I wired up the INA3221 with solar panel and CN3722 model and 3S lithium battery.
We could add more sensors to measure system's performance and critical points. I added two temperature sensors, one DS18B20 on battery's pack and one MCP9808 on solar panel. A lux sensor (MAX44009) is adhered on solar panel to measure solar irradiance in lux. IN addition, a Neopixel was used to indicate the battery's level.