EmonPi for Solar and Grid Import/Export

Getting Started
1

I’m am looking to setup a system to monitor my solar production, consumption, and grid import/export. I’m in the USA which makes things a little more complicated. Since both the solar and grid are split phase systems, I need 4 CTs. However, it appears I can ‘get away’ with 2 CT inputs if I connect the pairs of CTs per diagrams 5b or 5c of this page: https://openenergymonitor.org/emon/buildingblocks/EmonTx-in-North-America. In other words, the two solar monitoring CTs are paired and the two grid monitoring CTs are paired together: 4CTs, two inputs.

Given that I only need two CT inputs, I think I can use a emonPi rather emonTX. Does anyone have any experience with this type of setup? Any recommendations on which CTs to use, burden resistors, and preference for 5b or 5c?

I understand that I may have to desolder and add a different burden resistor, if necessary. I also realize that this will limit my system to only monitoring total power for the solar and grid, not individual phases. Will the emonPI still be able to measure real, reactive, and apparent power in this setup? Thanks

2

If you look harder at the N.America page, you’ll see a list of possibly usable CTs (check the aperture dimensions against your cables) and the burden values you need. We also know of the Sentran 100 mA range from Aim Dynamics, which I need to add to that page.

The emonPi runs basically the same sketch as the emonTx, but although currents and apparent powers are calculated in the same way, only the real powers and voltage are made available to emoncms for recording. To record those additional values, you’ll need to edit and reload the sketch, and adjust emonhub.conf to suit. We don’t measure reactive power, only real and apparent (therefore we don’t know whether the power factor is leading or lagging - this is also true for the emonTx).

If you want to monitor more circuits later, you can add an emonTx to the system.