Sawtooth signal when hybrid inverter supplying loads

I have a PV + hybrid inverter + battery backup system + critical loads panel. The CTs are installed on the mains and on the output of my PV system on it’s way to the inverter. (Yes, I have contacted sense support about this behavior)

When I’m running in “normal” mode, everything looks great in Sense. Things go a little sideways, however, if I program my inverter to power the critical loads from the battery when there’s no PV. When running in this mode, the Other bubble on the now page disappears and re-appears every second. The Solar tab shows power coming from the grid, then falling to zero, then coming from the grid, at the same rate the other bubble appears. On the power meter page, I see a weird sawtooth signal for the usage.

I’ve attached a screenshot of what the power meter shows. In this sample, battery discharge started at 5:00 am, and you can see the weird sawtooth signal when it starts. If you were to average out that sawtooth, it would be pretty close to my always on non-critical load usage (200-300w).

I’m curious if this just how it works when you have a hybrid inverter supplying power, or if there’s some setting or CT placement that might improve it. Sense is still doing what I need it to do, which is to tell me when I’m buying power from the utility, so getting this ironed out would be gravy.

Could you tell us a little more about your system? There are a few setup of the hybrid inverters… They almost all have a critical load/ priority load or essential load part. Typically how these work is the Inverter has a switch built in and turning normal mode it’s just like a regular grid tied inverter with the addition of a battery charger. When the grid goes down or if you have a tariffs change or even if you want to simply use you battery. There is switch that disconnects the critical load from the mains (most go into a sub-panel now) along with the actual inverter and instantly connects them to together which is then powered by the battery. When it switches to battery powered the inverter frq wouldn’t be sync with the grid which I would think if your sense CTs on the grid mains, they wouldn’t read the power going to your critical load while in this mode.

Some of them are kinda like an all in one hub and some have everything separate. Could you post us some pics?

Sure!

Here’s a diagram based on my understanding of the system.

Here’s a photo of the main service panel:

This photo (incorrectly) shows the solar CTs installed where the 40A comes in from the hybrid inverter. This is what I tried first, but could not get it to work as expected after a couple of iterations with sense support. It just didn’t seem to like having current flowing both ways across the solar CTs. After that, I just moved it into the solar subpanel so it would measure just the solar generation.

My primary objective here is to know if I’m exporting enough power to offset what I’m buying, which this setup provides. ( will update with photos of the interior setup forthwith)

Do you know if your transfer switch is a ATS (auto trans switch), a STS (static-auto trans switch) or a switch that is controlled by your hybrid inverter (separate wires)?

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Also I’m assuming your loads for your critical loads are separate and they don’t make a loop back and your parts labeled “micro-inverter” are actually “optimizers”?

None the less, the CTs for the solar would go where you have them in the photo. This would measure your total PV wattage minus what went into the batteries while in normal mode. When your running partially or completely on batt it wouldn’t read anything there.

I couldn’t find any hybrid inverter transfer switch that would work the way you have your diagram where you could run the inverter on backup mode with the grid still up . I think who ever installed this set it up to only be multi-mode hybrid meaning… Its only designed to work as grid tired when connected to the grid, they if the grid goes down, the transfer switch would flip allowing the loads you have in your critical load sub-panel to run from from battery.

What your describing where you are running off the grid and running off your battery supply would require the switch to be built in to the hybrid inverter which would be on the other side of the inverter. I think these are called an “solar-coupled hybrid inverters” which is setup to do what you are describing since some electric companies are charging special fees, changing on/off peak/ so that they make money on your grid-tied solar.

I believe the reason you are seeing the crazy graphing is because when you still on the grid and you turn your inverter to backup mode its turning it into “off-grid mode”. When its in off-grid (back-up) mode it will not match the phase with the utility sine wave since it is creating the sine wave. Compared to grid-tie (normal) mode which the inverter matches the waveform from the utility company. Therefor you have two waveforms fighting each other and that is what you are visually seeing on the sense meter charts. I would assume the meter base reading it is also confused and also not going to charge/ credit you accurately.

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