Emoncms app wrong calculation? [SOLVED]

This may be posting in the wrong forum, but I’ll give it a go. The emoncms solar web app is great as a dashboard, but I think it does something weird, see image.


which obviously is wrong since EXPORTING == USENOW when USENOW<0.
Once USENOW>=0, EXPORTING switches to IMPORTING, and the calculation is correct:

Not a big thing, but makesthis dashboard not very usable. Who are the right persons to either guide me (if my setup is wrong) or correct the app?

Let’s make sure you are sending the correct data to Emoncms. Can I see your Emoncms setup in IoTaWatt and your inputs screen in Emoncms?



And the web app:

Cumulative inputs are not right here, I have not configured them as feeds yet. And note that I log watts produced as a positive value. Just because I felt that looked more intuitively correct.

Still not a complete picture. I see how you get solar and solar kWh, but you are not showing where the use and use kWh are being developed.

I believe use for this app is expected to be a positive number, and that export is calculated as solar-use. When that yields a negative result, my recollection is that the metrics is renamed import and the absolute value is displayed.

So with that scenario, it appears your negative use is the problem and should be investigated. There are two basic ways that a solar inverter is connected: before the mains CTs or after. If connected before (on the grid side) then use is simply the mains power. If connected after (on the load side), then use is mains+solar.

So we need to know where the solar is connected, and how you are developing use and use kWh.

Hi, the things you describe makes me understand how my setup should be, I think.

The PV inverter (three-phase) is connected on the load side in my cabinet (not on the grid outside my fuse cabinet). The total load (also three-phase, I measure on all three leads and sum them) is the feed reported as USE NOW. This is of course net usage, and I now realize what I need is a gross usage feed. Which would be, as you write, the mains fuse load + the solar production.

So, I will need to figure out how to create a feed for gross load. I am not fluent in emoncms configuration yet, so I could use some advice. Especially since the mains fuse is logged by Iotawatt unit 1, while solar PV is connected to Iotawatt unit 2 (both fully visible in my emoncms).

I think I got it right:

So would this be the correct setup?

It does say “cumulative … in kWh”, is that the normal power-to-kWh feeds or kWh accumulated from t0?

Maybe. The question in my mind is what happens when unit 1 posts before unit 2? Does the process list just use the last value it had for unit 2? I don’t think it’s sophisticated enough to recognize the dependency, and while using the previous 5 second value shouldn’t be a big problem, the implications of what happens when both units are trying to recover from an outage could introduce serious error.

I don’t have a solution other than to recommend you measure both the mains and solar with the same IoTaWatt to synchronize the posting to Emoncms. If you have three inputs free on unit2, you could add another set of CTs to replicate the mains there as well.

I see your point. Since I am on my way to move everything to a new emonpi anyway, I can take the job of re-wiring the CTs as well.

Thanks for your help!

System working fine now, timing of data doesn’t give any obvious errors during stable operation.
This is bit up north in Norway mid October. Sun is not very high and up only there for a short time. But still my 22m2 produce and give significant net reduction since startup this April.

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