Total output not adding up, misunderstanding or misconfiguration? - Resolved

I recently set up an IoTaWatt as a way to track solar generation in my home (In the USA, with 240v split-phase L1-L2-N). I have one 6kW inverter attached to the main feed going between my utility meter and my main panel (with a pair of inline taps). I have a 7kW inverter attached to a subpanel off my main panel with a 50A double pole breaker. Input 1 and Input 2 on the IoTaWatt are around the main feed between the meter and the main panel. Input 2 and Input 3 are around the L1 and L2 going to the subpanel.

The output labeled “Main” in that screenshot is simply Input 1 + Input 2 in Watts. Input 1, 2, 3, and 4 are all set to allow negative values.

When this screenshot was taken, one inverter was generating 5,147W and the other was generating 4,669W. Am I correct in assuming that the CTs around the main panel feed should be seeing -5,147 + -4669 - the home load? The average load for this home is around 500W, with some peaks up to 1500W if someone turns on a microwave or toaster oven. I expected to see the value of “Main” to be closer to -9,300W. One of the inverters also has CTs around the main panel feed, and it shows around -9,050W. Am I missing something that would cause the value to be about 2,000W less than expected?

Thank you!

It’s going to be hard to exactly reconcile this with only the mains and subpanel monitored and a general estimate of the house load. There is also a question of where the mains CTs are with relation to the 6kW inverter feed. Both are described as “between the meter and main panel”. I’m assuming they are between the meter and the 6kW inverter tie-in, but that needs to be clarified because there is a discrepancy between the two mains that is in the order of what you say is missing.

The difference could be:

  1. A really significant 120V load on Input_2.
  2. A misconfigured CT on Input_ (200A CT configured as 100A)
  3. The CT on input_1 is between the 6kW inverter feed and the panel (rather than upstream between the meter and the 6kW inverter feed)

I’m going to put my money on number 2, with number 3 as my fall-back.

Thank you for getting back to me so quickly. To clarify, the CTs for Input 1 and Input 2 are supposed to be on the main feed, between the tap point for the 6kW inverter and the meter. I say supposed to be, because I had a really hard time fitting two 200A CTs (one for the inverter’s diagnostics and one for the IoTaWatt) on the line and now i’m wondering if I put the Input 1 CT on the wrong side of the tap, which would explain the large difference between Input 1 and Input 2.

Followup question, if I got smaller CTs and put them on the tap line that goes between the main line and the 6kW inverter, would that show just the solar generation from that inverter? I’m assuming power should never “flow” toward the inverter, since it has no loads, correct?

Thank you!

EDIT: It was option 3, I had one CT on the wrong side of the tap.

Yes, for all intents and purposes (see next answer)

Actually, most inverters draw a little bit of standby power when not producing, typically a few Watts, but it’s not significant in the big picture.

If I could make a suggestion:

Place the main CTs between the 6kW inverter tie in and the Mains. Then put one of those 50A CTs on one of the inverter lines. With that, IoTaWatt will be able to monitor the output of the 6kW inverter (most US inverters are two-wire so you can just check “double”).

If the feed for the 7kW inverter is anywhere near the IoTaWatt, place the other 50A on one of the feeds from that inverter - same configuration with “double”. Now you will know the generation of the 7kW as well, and by adding, your total production each day.

Lets say you call the 6kW solar6 and the 7 kW solar7. Your mains main1 and main2.

Total solar production is solar6 + solar7.
Total consumption is main1 + main2 + solar7

Note that solar should be positive when producing and negative for any standby power.

You could feed those metrics to PVoutput and get a nice display:

Looks like I need to make some more purchases in the store. I don’t think I can get the 50A CT around the line for the 6kW inverter, since they had to use a tap the wire gauge is the same as the main feed for the house.

When it’s connected that way, there is usually a separate box with a circuit breaker. The fat wires probably only go to that box, and from there the wires to the inverter should be no larger that #8. If that box is nearby, you could grab the 6kW from inside that box on the thinner cable to the inverter.

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So, I finally got all the parts and got around to hooking things up, and the results are…interesting. What orientation should the CTs be in this scenario?

I went through and checked the “Reverse” box on the necessary inputs, so that power consumed would be a negative value and power generated would be a positive value. Now I am seeing the inputs change between positive and negative seemingly at random (but always one leg, never both).

For example, during the day when solar power was being generated I had values like this:

Input1: -3000
Input2: -2500
Input3: -2000
input4: -1500
So I checked the “Reverse” box on the input settings, and everything flipped to positive like this:
Input1: 3000
Input2: 2500
Input3: 2000
input4: 1500
Then I checked back an hour or so later, and the status page looked like this:
Input1: -3000
Input2: 2500
Input3: -2000
input4: 1500
So I unchecked the “reverse” box on input1 and input3, thinking I must have forgot to refresh the page, or maybe something got stuck the first time. The values returned to:
Input1: 3000
Input2: 2500
Input3: 2000
input4: 1500
Then I checked back a few hours later, now that its dark and solar generation is at 0W, and it looks like this:
Input1: -105
Input2: 350
Input3: -400
input4: 687

Either i’m losing my mind or I have badly missconfigured/misunderstood something.

For what its worth, the new CTs I put in for the tap between the main line and the 6kW inverter, and on the 7kW per your recommendation are working great.

At this point I have no idea what your configuration is. Can you post a picture of the installed CTs and label them as to which input they are connected to? The way we left it you have the two mains and two inverters.

I think I figured it out. It was a dumb mistake on my part. The 7kW inverter is a hybrid inverter with 20kWh of battery capacity. I had changed it from “Backup Mode” to “Self Use mode” to show a friend how the system works and forgot to change it back.

In “Backup Mode” the batteries don’t do anything unless the grid goes down, then they provide backup power. In “Self Use Mode” I did not realize that the system will use the batteries to power the house until they drop to about 50% capacity, and then switch back over to the grid. This is why the IoTaWatt was seeing “solar generation” after the sun went down. On top of that, the reason I have the batteries is because I have three electric pumps and a dehumidifier keeping my basement from filling with water. Thats four large 120v devices on different circuits that would randomly cycle for between 2 and 6 minutes, explaining why I would see single inputs suddenly reverse, only to change back again at a later time.

I have now had one solid day of all of the values making sense, generation is being tracked in PVOutput and InfluxDB. Thanks for all the help!