EmonCMS, odd graph showing power consumption tracking to solar generation

Hi All,

I’m looking for some help for and seemingly odd graph I’m getting for the garage power consumption that seems to be tracking (a bit) to the solar generation, and advice on what more I could be tracking logging.

Some setup info:-
EmonPi located next to an secondary (annex) consumer unit with easy access to data etc
CT 1: is on the main annex incoming line
CT 2: is on the Solar PV generation line

EmonTX located on the main house consumer unit.
CT 1: is on the main household supply
CT 2: is monitoring the water well pump
CT 3: is monitoring the shower pump and immersion heater
CT 4: is monitoring the supply going to the garage

I was looking at the garage graph and noticed an unusual increase in consumption that seems to track with the amount of solar being generated.

The 75w spikes would be the freezer and the general load mostly just a PoE switch

Same graph showing the solar generation (best generation day since I installed the EmonPi!)

There is nothing in the garage that would consume like that, so I’m guessing I’ve messed up the logging? If so what might I have done and how do I fix it :slight_smile:

Hopefully it’s helpful to show the input’s for both:-

Anything else I should log maybe to add to a dashboard?

Thanks for your help!


Hello @Techno that’s interesting, what does the house voltage look like over that period, could there be a relationship with garage temperature?

Hi Trystan,
Unsure, I assume I’ll need to log the Vrms feed from the EmonTx?

I don’t see how the temperature would effect it. If the freezer was getting warmer I would expect it to increase it’s running time. The cable to the garage runs externally for a while then underground but it’s shaded in the morning so I can’t see it related to that.

It might be worth pointing out that the garage CT clamp is using the high sensitivity port on the EmonTX… If that makes any difference.

I’ll add a local power monitor plug to the various bits of kit in there and see if that can see any changes.

Kind regards,


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Yes great, I doubt it’s that but worth checking.

Initially I wondered if there was some kind of interference effect between CT channels but its hard to see how that would happen given that the solar CT is on the emonPi and the garage CT on the emontx in a different location… puzzling!

You’re looking at an uplift of about 12 W, that’s 50 mA or so. Is the mains wiring correct? – meaning, is the solar neutral returning to the right place, and the Garage c.t. is not seeing some stray leakage current?

How does the Annex C.U. receive its feed? Is the outgoing cable to the Annex right next to CT 4?

Messed up the logging? – You are adding 12/3000ths somewhere? How? That’s highly unlikely.

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They will be close, will a look when I next get a chance. How close is too close?

Here are some graphs showing voltage as well, interesting 13(ish) volt difference, is that a calibration issue I need to address?

Garage Consumption

Garage Consumption and Solar generation

Voltage measured by EmonPi (Anex) and EmonTX (Main)

Yes - or rather, most probably yes. You might have a small voltage drop along a long cable, but the rules state that your wiring should be designed so that it doesn’t exceed 2.5% at the design current. It’s easily fixed in emonCMS, but bear in mind that doesn’t also calibrate the power.

The numbers I managed to get are in Issue 6 of the c.t. test report in ‘Learn’ (not checked again for the latest c.t’s):

  1. Effect of an adjacent current-carrying conductor.
    To measure this, a large coil of 20 turns carrying 5 A, oriented so as to simulate a parallel
    conductor carrying 100 A, was used. The current transformer under test was outside the
    coil. The equivalent current is the current that the CT would have measured in a conductor
    passing through the CT.
Distance Equivalent Current
Touching 160 mA
20 mm 110 mA
50 mm 44 mA
100 mm 15 mA