I'm reading data from the charge controller every 30 seconds and every five minutes I write out the values into the RRD. 288 records of the five minute data are stored which should be one day. Every hour, the five minute data is averaged and stored and 168 records are stored which should be one week's worth. 365 daily averages are stored. Since only the summarized data is stored, the database never gets that large. After I get a couple of weeks worth of data I might add an yearly graph.
The table on the page shows the most current data and is updated every minute. "Array Voltage" is what the charge controller is seeing from the solar panels. The "Reference Voltage" is the target battery voltage for the charge controller. At this point that is the temperature compensated absorption voltage. "PWM Duty Cycle" is a measure of how much of the current is actually being used to maintain the battery at the absorption voltage. I still need to add some credits to the bottom of the web page.
Where the array and the battery voltage lines diverge in the graph on the upper left around 1:30pm is where the charge controller switched from bulk to absorption charging. At 3:55pm, I started the rice cooker running on the inverter so it switched back to bulk charge. The power is just the current and the battery voltage multiplied together. So it's sort of the same info. I'm not sure which one I'll keep.
|Raspberry Pi 3 model B|
Image is from the Adafruit site