Clipping issues due to export limit

[davesbell]

I expect I'm doing something wrong or not understanding how something works. I don't think this is actually a bug, just user error.

Describe the bug
Predbat doesn't detect that clipping is going to happen, and keep that information

Expected behaviour
I've got an 8kW export limit, but a 12kW array. I would expect when I'm getting towards 8kW of generation, Predbat would notice that and limit what is in the battery to take the overflow.

It does seem to do this for the following day, but when that day rolls around it all seems to be lost.

Predbat version

v8.37.3

Environment details

• Sigen Sigenstore 12kW invertor with 20(ish) kWh battery storage
• Standard HAOS install
• 2 solar arrays. 1 north, 1 south. Both in Solcast.

Screenshots

This shows that generation will be just below my export limit today. I'm not sure this will actually be the case however.

Log file

predbat.log

Predbat debug yaml file

predbat_debug.yaml.txt

predbat_plan.html

apps.yaml.txt

[daviessm]

See also #1206

[gcoan]

Describe the bug
Predbat doesn't detect that clipping is going to happen, and keep that information

Expected behaviour
I've got an 8kW export limit, but a 12kW array. I would expect when I'm getting towards 8kW of generation, Predbat would notice that and limit what is in the battery to take the overflow.

It does seem to do this for the following day, but when that day rolls around it all seems to be lost.

Could you explain a bit more about what is actually happening, I don't really follow it based on the graph.

In terms of what Predbat does (or should do) assuming you have set the export limit and inverter/battery rates correctly in apps.yaml:

First predbat doesn't control export limit. It relies on the inverter to do that, but it should be aware of it and take account of it ...

If you turn the HTML plan debug on then you will see an extra clipping kWh column which is where predbat predicts there will be clipping.

What predbat should do is then manage your battery level so you can (where possible) store excess solar generation in the battery. You will see forced exports in the plan where predbat is lowering the SoC to take the excess solar and avoid clipping.

Obviously the generation might be such that Predbat can't always do this and you'll still get some clipping, but it should try.

Of course generation could be significantly above forecast and you get extra unpredicted clipping, or it could be below and predbat empties the battery when it wasn't needed to. Not a great deal predbat can do about that, other than try to get your solar forecast as accurate as possible.

And finally to say that per the linked item, when predbat sets freeze export mode it assumes that all solar is exported and doesn't go into the battery. Some inverters have a Feed in first mode whereby solar is exported but once the export limit is reached they will charge the battery. Predbat doesn't currently have a concept of this (so the plan will be wrong) although it has been requested. From what others have said, the setup of your Sigenstore doesn't do this, all solar is exported and any excess is clipped.
Note this behaviour is only in freeze export mode. If the plan is in Demand mode then predbat should try to reduce clipping

[davesbell]

Sorry, that graph was a bit useless.

First predbat doesn't control export limit. It relies on the inverter to do that, but it should be aware of it and take account of it ...

Understood. That is my expectation. I've set the export limit in my apps.yaml. Full copy is attached if you're interested.

If you turn the HTML plan debug on then you will see an extra clipping kWh column which is where predbat predicts there will be clipping.

I thought this was also attached, but I see the thing I downloaded didn't include it.
Predbat never predicts clipping (except on an evening when it's trying to dump the battery). I wonder if its because generation is still a bit marginal compared to my export limit, but we do often get above it. The array is new as of Jan, so I'm expecting as the months progress this to happen more often.

What predbat should do is then manage your battery level so you can (where possible) store excess solar generation in the battery. You will see forced exports in the plan where predbat is lowering the SoC to take the excess solar and avoid clipping.

Obviously the generation might be such that Predbat can't always do this and you'll still get some clipping, but it should try.

This is exactly the behaviour I'm expecting but not seeing. As I mentioned I'm fairly sure this is a user error, but I was hoping that on sunny days predbat would hold spare capacity in my batteries to soak up the extra sunlight, but it seems to like them sitting at 100% no matter what the conditions are!

I am wondering if it is just because the generation is a bit marginal at the moment towards my export limit. Maybe when it gets to May we will see it behaving as I expect?

[daviessm]

I think part of the problem is that Predbat sees the generation forecast as static values rather than an average - yes, there might be 4kWh produced in a given half hour period but in reality it might be made up of 4kW for 15 minutes as clouds pass then 12kW for 15 minutes when they're gone. If they battery's full and you have an 8kW export limit then you're going to lose the 4kW above that when the clouds are gone (assuming no load, my maths is probably wrong there but hopefully you get the idea). Whereas Predbat plans for the generation to be a steady 8kW and if that were the case, there'd be no clipping.

From your HTML plan it looks as though there's no forecast higher than your export limit of 4kWh per half hour, especially when taking into account load as well. My understanding is that Predbat always takes the "forecast" and adjusts it down towards the "forecast 10%", never above it. I've set my PV scaling setting to 1.25 to try and counteract this, as well as slightly oversizing the arrays in Solcast.

[gcoan]

Originally predbat did model solar as being flat across the period, but with the introduction of cloud coverage https://springfall2008.github.io/batpred/customisation/#cloud-coverage-and-load-variance it tries to model the passing of clouds to vary the generation over the half hour period.
Personally I found that this gave chopping and changing on the model so I turned it off, but its on by default

From your HTML plan it looks as though there's no forecast higher than your export limit of 4kWh per half hour, especially when taking into account load as well. My understanding is that Predbat always takes the "forecast" and adjusts it down towards the "forecast 10%", never above it. I've set my PV scaling setting to 1.25 to try and counteract this, as well as slightly oversizing the arrays in Solcast.

Correct, predbat modulates downwards based on blending PV10. If you find your PV is above the PV50 then try increasing the solar efficiency in solcast (assuming you are using that).

The other thing that will adjust your PV is predbat's PV calibration which adjusts the PV based on historical generation vs forecast. Personally I don't use this, but that could be an option if your PV is consistently better than expected.

And if you find predbat doesn't forecast clipping then try reducing your export limit in apps.yaml. I have mine set artificially lower to force predbat to be more compensatory for higher solar

[springfall2008]

There's certainly something wrong here as there is clipping predicted when there is no solar, debugging

[springfall2008]

The above fix was released, please let me know if it helps