On Monday 02 July 2012 08:20:16 Simon Hobson wrote: > Joel HATSCH wrote: > >My inverter (SMA) records every 5 minutes the instantaneous power and the > >overall yield (both in kW (resp kWh), float with 3 decimal places). > > I'd say use the counter. I assume the instantaneous reading is > actually for the instant read rather than an average over the > previous 5 minutes and so may well be significantly different.Long > term it will probably average out and be fairly accurate, but short > term may be way out. > Eg, if a cloud passes over the panels just as you take a reading, > then you may get a low figure when output is actually high. > Similarly, if a break in the clouds passes just as you take a > reading, you'd get an artificially high figure. > > > Since you aren't likely to want anything other than kWH in your > output, I'd suggest just storing that. Internally it will be stored > as KWH/s (all things are stored as rates) and so on output you'll > need to multiply by your time span to get a total amount of energy. > Eg, if doing daily figures, multiply by 86400 and you'll kWH/day. > > Also, since your inverter is keeping the counter, you could afford to > increase the heartbeat considerably. If you fail to collect data for > a while, then your next collection will result in a big chunk of > lecky being counted but it will be spread evenly through the > intervening data slots. You'll lose the detail of when it was > collected (eg a couple of days would show as a flat line at whatever > the average rate was) but your totals would be correct and after > consolidation you'd probably not notice it on the "one period/day" > long term graphs.
Thanks to you and Steve for the hints. I knew I was missing something very obvious... data is stored as rates, therefore you must multiply it by the period of integration/time. Was still thinking in discrete data series inside my spreadsheet. I gave it a try, works as expected. Now I just need to do some fine-tuning with the graphing parameters to get my reports. Joel _______________________________________________ rrd-users mailing list rrd-users@lists.oetiker.ch https://lists.oetiker.ch/cgi-bin/listinfo/rrd-users
