Daily logging of produced energy from solar inverter

[tintsch]

Hi,

I'd like to log the daily energy production (kWh) of my solar inverter.
I created a scheduled script running once a day. This script reads the energy production of the previous day from the inverter.

Is it possible to save daily data consisting of a timestamp and a value?

I tried to save it with the following script, but obviously the value of 'pv' gets overriden every time.

Code:

save = {
  ["Pac"] = PV_Pac,  -- PV_Pac is set to the energy value coming from the inverter
  ["timestamp"] = os.date('%Y-%m-%d', os.time()-24*60*60)  -- yesterday's timestamp
}
result = storage.set('pv', save)

Can data be appended with the storage object? Or how could this be accomplished?

The goal of this logging is to produce bar charts later on.

thanks!
Valentin