[rrd-users] Handling solar inverter data in rrdtool ?
j-ml at joel-hatsch.net
Mon Jul 2 00:51:49 CEST 2012
I'm trying to feed data from my solar inverters into rrdtool and plot some
nice pics out of it. Using google, I have found several websites explaining
how to generate nice looking pics, but I didn't found a description of the
database schema and data feeding.
My inverter (SMA) records every 5 minutes the instantaneous power and the
overall yield (both in kW (resp kWh), float with 3 decimal places).
If I store the values as GAUGE, I can draw daily production curves out of the
instantaneous data, but I can't put them in a RRA - AVERAGE'ing or MAX'ing or
LAST'ing instantaneous production makes no sense, only the sum
Regarding the overall yield, if I declare it as COUNTER (always increasing
value) and use the LAST function to compress a whole day of data, I can plot
the data, but as it is absolute, I get e.g. 40KWh increases from 3500 to 3540,
however I'd like to see a graph where 40KWh are plotted for that day (i.e.
data always ranging between 0 and 50kW for each day, not continuously
Moreover, COUNTER data seems to be divided by 300 (5 minutes) to get a
frequency. I worked around this by multiplying the data by 300 in a VDEF
As far as I understand, I'll have to do either some pre-processing (before
feeding into rrdtool), or some post-processing on the data (when plotting the
pics). To use COUNTER I have anyway to multiply the data by 1000 to convert it
My question : what's your advice on the data structure (DS, RRA), and on
how/when to do the data conversion
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