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. -- Simon Hobson Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed author Gladys Hobson. Novels - poetry - short stories - ideal as Christmas stocking fillers. Some available as e-books. _______________________________________________ rrd-users mailing list rrd-users@lists.oetiker.ch https://lists.oetiker.ch/cgi-bin/listinfo/rrd-users
