Of course I had to have one, that was a given. Why? Apart from "just because", "solar is cool" etc, the scientific reason is that my less often used old hobby cars really need a battery charger to keep them topped up in-between uses. An Interwebs mail order was completed and praise the universe, it arrived before the weekend. So I climbed on the garage roof, installed the solar panel and wired it up to the included charge controller, and the battery of one of my hobby cars, the 1985 Audi 100 C3.
But how to quantity my sense of self satisfaction? Easy, ESPHome and Home Assistant of course. I had a few spare power monitors, an INA260 and INA226. These modules are very simple to use, they come with screw terminals and they use the standard I2C comms protocol.
ESPHome has support for these modules: https://esphome.io/components/sensor/ina226.html and https://esphome.io/components/sensor/ina260.html. The INA260 is probably technically superior, because the shunt resistor is internal to the chip rather than relying on an external one mounted on the board. I imagine the tolerances are probably tighter for the internal one.
(The shunt resistor is a very, very small resistance usually in the order of 0.01 Ohms or less, which the electrical load is passed through in order to measure the current using .. ugh maths ... Fundamentals of Current Measurement: Part 1 – Current Sense Resistors)
Anyway, those two modules and a spare D1-Mini ESP8266 were what I had available in the workshop. A rats nest of wires but it performs the required function, measuring my sense of self satisfaction 😁 The brown figure-8 wire at the top goes to the car battery, the black one at the bottom left is the supplied 5 metres of wire to the solar panel. The charge controller even has USB ports which I've used to power the ESP8266.
One day when I get around to it, I'll share my overall Home Assistant and ESPHome implimentation. At this time I'm up to about 20-ish ESP8266s which do various lighting and sensor duties about the house. This is what the two power monitors look like in Home Assistant:
(Yes I know, I wired the battery wire backwards and the current flow is negative. I'm too lazy to either change the wires or chuck a negative "filter" in the ESPHome yaml file. Ironically that would have been quicker than typing this explanation....)
So there it is - in the winter sun at about the middle of the day, almost 11 Watts of energy from the sun. There's a slight loss in the charge module of course, and the ESP8266 itself would be robbing a small amount of power, but a still useful 10 Watts is being fed into the battery of the car. Sense of self satisfaction has been measured and displayed in real time ✔️
