KWH meter discrepancy [RE-wrenches]

[Joel Davidson]

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> 3) Most revenue grade kWH meters are very accurate in the "forward"
> direction (+/- .5%), but wildly vary in their accuracy when running
> "backward". This aspect is huge on a number of fronts and there isn't room
> to describe the plethera of scenarios here. You may be wondering "why 
> would
> my PV meter run backward?"... Simple.  At nite, the inverter uses some AC
> power... A very small amount based on the Manus, but some nonetheless.  It
> is impossible to tell here what that effect has on the "dial readings". 
> The
> Inverter displays do not count this.  For starters, you will have to know
> whether or not the PV meter is detented or non-detented.  After that you
> will have to find out whether or not it is calibrated to meter
> "bi-directional" or not and the accuracy tolerances for both.  Good luck
> getting that info!

Hello Matt - I can't recall the source or the exact numbers, but a survey of 
calibated and certified electromechanical revenue grade kWh meters showed 
over 1% inaccuracy forward and over 3% inaccuracy backward.

Inverter manufacturers - Do you have 3rd party verification of meter 
accuracy?

Joel Davidson 


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