Export vs Freeze Export

[rogerlittin]

I've been using Prebat for a while now, and have been trying to figure out some settings that work. My system is a 8kW Sigenergy inverter with 27kWh battery and 11kWp solar panels across two roof aspects. I have a 3.68kWh export limit. My import tariff is IOG, and export is Outgoing Octopus.

Left to its own devices, Predbat will fully charge the battery, starting at 23:30, and is usually full by 02:00. It will then export a bit and then replace this by 05:30. It may then export a bit more before sunrise, and on most days, the battery level is between 80 or 90% when solar starts coming up to a reasonable level to sustain house loads. Usually, it will then switch to Freeze Export. If the battery level is much below 80%, then it will switch to Demand mode and fully charge the battery again. Forced export starts around 18:00, and by 23:30, the battery is down to about 10%.

This happens wether it's a overcast day or completely cloudless. The end result on a day with good solar potential is that either the battery is held at 80 - 90% by the Freeze Export setting, or the battery is fully charged by mid morning. Either way, severe clipping occurs for most of the day.

On most days, the Solcast forecast and the actual solar (without clipping) are fairly close, but I think that the clipping calculations in the plan, with debug enabled, are a bit off. Actual clipping will normally occur around mid morning but the plan shows it may occur for a short time in the afternoon, if at all. The actual PV estimates are well above what would cause clipping.

I'm not sure if it's just the way the integration works with the Sigenergy inverter, but it seems strange that Freeze Export clips excess solar instead of sending it to the battery.

If I can intervene early enough, I can set Manual Export from 05:30 until later in the day, so that the battery level is fairly low by the time the solar export starts, but then If I don't keep setting it, then it will switch back to demand mode, and try to fully charge the battery again. On very good days, I've got to set Manual Export for most of the day to avoid clipping.

Is there a way to have Predbat prefer Export over Freeze Export, and for it to make sure there is sufficient battery capacity available at the start of the day to be able to handle the excess solar instead of allowing clipping to occur. I would prefer if it would maybe stop exporting a bit earlier in the evening if there wasn't enough solar, instead of not exporting earlier in the day and then clipping the excess solar because it has nowhere to go.

What is strange, is that in the plan, tomorrow almost always shows what I'm wanting to achieve. It's almost all yellow Export slots, but these switch to something else once tomorrow becomes today.

[gcoan]

it seems strange that Freeze Export clips excess solar instead of sending it to the battery.

This is normal behaviour, freeze export stops the battery charging, and all solar is exported (and in your case with a low export limit, often clipped) https://springfall2008.github.io/batpred/what-does-predbat-do/#predbat-modes

You can turn freeze export off if you don't want predbat to use it, but it tends to be used if predbat thinks your battery is sufficiently charged for the day and there's no benefit to charging it further.

Assume you have set your export limit correctly in apps.yaml?

Diagnosing what is right or wrong with the plan is difficult without seeing the plan and your config. You can use the select.predbat_manual_xxx controls to overwrite the plan if you want, and can put these in an automation if you want to change predbat's behaviour.

[daviessm]

You're right about predbat's plan. I raised #3757 about this - it correctly predicts battery SoC increase for force export, but not freeze export.

[gcoan]

I will separately look at 3747, but my initial reaction is that this is not a predbat bug, just a feature of the FoxESS inverter which doesn't behave as predbat expects it to.

Just to highlight: Predbat is a generic battery optimisation engine that has been configured to handle different inverter types. Predbat can't be expected to handle the differences of different inverter types, it has a model of how the inverter should behave, and the work to integrate new inverters is basically to set them up so they work as predbat expects.
Having said that, it is not beyond the bounds of possibility that predbat can be enhanced (in a generic way) to handle additional inverter behaviours.

[daviessm]

Are there any hybrid inverters that throw away/clip PV power when they're told to prioritise export and there is space in the battery? That seems odd.

Predbat can't be expected to handle the differences of different inverter types, it has a model of how the inverter should behave, and the work to integrate new inverters is basically to set them up so they work as predbat expects.

You're saying inverters are expected to charge the battery while force exporting, but not when freeze exporting (prioritising export) and that when it doesn't happen it isn't a bug in the prediction model, it's a feature of the inverter?

Please don't be so condescending when replying to people. It's putting me off contributing and more code to the project.

[gcoan]

Are there any hybrid inverters that throw away/clip PV power when they're told to prioritise export and there is space in the battery? That seems odd.

Lots of inverters are different. The raiser of this issue asked "it seems strange that Freeze Export clips excess solar instead of sending it to the battery" and wondered if this was a feature of their inverter setup.

I explained how predbat expects the inverter to operate, and quoting from the description of freeze export mode, "The battery is in demand mode, but with charging disabled. The battery or solar covers the house load. As charging is disabled, if there is excess solar generated, the current SoC level will be held and the excess solar will be exported..."

This is exactly what my inverter does. When set to freeze export, predbat disables battery charging which means that all solar generated is exported. The inverter is not told to prioritise export, it is told to stop charging.

Suggest the conversation continues on 3747 that you raised about how your Fox ESS inverter behaves with predbat.

[rogerlittin]

@daviessm, The Sigenergy inverter doesn't have an option to prioritise export over charging when running in Remote EMS mode. When Freeze Export is set, then it adjusts the battery limit to 0 so the battery doesn't charge. It is possible to set the priority on the inverter directly by using a custom mode, but then I can't control it remotely using Predbat. I did reach out to Sigenergy support this week, and they said they will consider adding solar priority as a feature when running in Remote EMS mode. After doing the research, it's not a predbat issue, it's an inverter issue.

@gcoan, I tend to agree with @daviessm, in that if the inverter supports it, in Freeze Export mode, excess solar should be stored rather than clipped. To me, that mode says export excess solar rather than store it. Hopefully, Sigenergy will fix it so this happens.

On a related note, today was a very good day for solar, and to my surprise, Predbat actually set the mode to force export for most of the day. It had fully charged the battery overnight, so I still ended up clipping from about 2pm, but that's better than clipping from 10am. I think now my task will be to try and figure out how to throttle overnight charging if the solar forecast is good.