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Discuss Export or Import in the Solar PV Forum | Solar Panels Forum area at ElectriciansForums.net

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gazandwiz

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Hi All.
New poster here and I'm posting because of the bewildering amount of differing information I'm finding on the internet.
My question is; How do CT transformers on the PV 'out' and the import meter 'in' know if there's an overall excess of deficit?
I've been looking at the Owl Intuition product for monitoring import, generated and exported totals, but can't work out how it's done if the CT transformer can't determine the direction of flow.

I have two arrays with two inverters. 3+1kw and am currently using an Owl CM119 to monitor the total generated from both arrays. I have the Live of both arrays going through the single CT transformer. My understanding of the OWL Intuition product is that it has 2 CT's and it looks at the difference between them when one is between the consumer unit and the import meter whilst the other is on the PV side. I can see two scenarios where the difference would be identical but the flows opposite.

1. I generate 3kw and have a 2kw load from my house. Net difference 1kw being exported.
2. I generate the same 3kw but have a 4kw load on my house and since the flow direction can't be determined the net difference is again 1kw, but in this instance I'm buying it from the power company. Wouldn't this mess up the statistics for the totals?

Have I misunderstood something? Does the Owl really work this way? I have emailed Owl, no response!

No doubt any responses will stimulate more questions, so if any one knows of a technical site that fully explains all this, I'd appreciate a link. You can't trust those making money out of selling kit for info!

Cheers

Gary
 

Worcester

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Mentor
Arms
For the best answers as to how the CT's work have a look at this site, it'll tell you "Everything You Wanted to Know About .... Energy Monitoring" including what's up with Owl's and all the other standard off the shelf energy monitoring devices, why they are so inaccurate and why they don't know which direction they are coming from :)

Home | OpenEnergyMonitor

especially read the forum posts : Forums | OpenEnergyMonitor

And the site is free!!
 

SolarCity

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Arms
What about standard import meters with CT metering? Presumably these measure export as being import? Has anyone else noticed this problem?
 

Worcester

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Mentor
Arms
See my other posts re Immersion heater stuff, all the meters that use CT that we have used also have a voltage and phase angle sensor - there is a sensor link to each of the phases.
 

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