Ignore Solar PV for Planning Purposes

[AberDino]

As per one of my previous posts, my goal is to export all of my solar PV energy, so that's the solar PV energy over and above the house load, as well as the solar PV energy which is used to meet the house load. The former is easy to achieve with Predbat, and the latter can be achieved with a bit of automation (work in progress for me).

Predbat is currently configured to use Solcast data, so based on the solar output forecast and historical house load (and given the import and export tariffs) it works out the optimum (most economical) overnight charge level for my battery. However, as I will be manually exporting the solar PV energy which was used to meet the house load, Predbat won't be aware of that when creating the plan, and as a result the battery might not be charged sufficiently overnight.

As a workaround, I could always force-charge the battery to 100% overnight, but as a result I might not drain down the battery sufficiently on a regular basis. I'm not sure, but I think Predbat will try to optimise the battery utilisation, so ideally I would like Predbat to remain 'in charge' of the battery.

Effectively, what I would like is for Predbat to ignore the solar PV contribution when creating the plan. I could do that by removing the solar components, but would switch.predbat_set_export_freeze and switch.predbat_set_export_freeze_only still work in that scenario, to automatically export excess solar energy rather than charge the battery? Also, it would be good to see the financial aspects of the solar PV element, and removing the solar components would make it more difficult to compare tariffs.

Any suggestions as to how I could accomplish what I want to do?

[gcoan]

I don't understand why you can't use Predbat's normal capabilities and need to start hacking bits of predbat around. Don't understand what you mean by manually exporting the solar PV either.

By default Predbat will work out your most optimal plan for using your battery and solar, so if your overnight import rate is lower than your export rate than predbat should charge your batteries up fully so that all your solar is exported during the day.

However, as I will be manually exporting the solar PV energy which was used to meet the house load, Predbat won't be aware of that when creating the plan, and as a result the battery might not be charged sufficiently overnight.

If you tell predbat that you are doing manual force exports (select.predbat_manual_export) for certain time slots, predbat will take account of that in the plan.

I might not drain down the battery sufficiently on a regular basis. I'm not sure, but I think Predbat will try to optimise the battery utilisation, so ideally I would like Predbat to remain 'in charge' of the battery.

Predbat doesn't optimise the battery for any kind of battery health, it does cost (and optionally carbon) optimisation. If you want to ensure the battery is fully cycled you'll need to put some force commands in to drive the battery to full or empty

[AberDino]

Hi @gcoan, first of all, many thanks for responding so quickly as usual.

Rest assured I would very much like to keep the 'hacking' to an absolute minimum, so hopefully it is just my lack of knowledge of Predbat's capabilities.

Setting the scene: I will hopefully have a second AIO up and running over the next month or so, and the two AIOs have enough capacity to meet the daily house demand. My overnight import rate is 6.6 p/kWh and my export rate is 15 p/kWh. I'm not allowed to export brown energy, so hence why my objective is to export all solar energy only. I don't want to 'dump' any excess charge from the batteries over and above the amount of solar energy generated on each particular day, hence why I use the switch.predbat_set_export_freeze_only switch.

Unless I'm missing something, in my case, the optimal (financial) plan would be to sufficiently charge the batteries overnight to meet the house load for the upcoming day and export all solar energy. However, it is my understanding that solar energy will always be used to meet house load in the first instance, and any excess solar energy can then be exported (or used to charge the battery). In my case, would you expect Predbat to manage the system such that solar energy used as house load will automatically be exported as well? If so, then I will be very happy indeed and I won't need to make any changes! If not, that's why I'm looking to manually export that quantity of solar energy which was used as house load (~2,500 kWh/annum in my case, so hence why it's important to me).

In terms of Predbat taking account of manual forced exports in the plan, the issue is that I won't know the night before if, or how much, I'll be manually exporting the next day, as that will all depend on the actual solar energy produced as the day progresses, so the manual exports would not be part of the plan as and when the batteries are charged overnight. However, I do know that I'll be exporting all solar energy produced during that next day, so the charge plan will always be correct if Predbat would assume there is no solar contribution. But, hopefully Prebat will recognise the value of exporting all solar energy, and I won't need this...

[gcoan]

Thanks @AberDino for the extra explanation, it makes much better sense now.

switch.predbat_set_export_freeze_only is definitely what you want to turn on to force solar to be exported during the day and not charge the battery, but this alone won't give you all that you want.

Unless I'm missing something, in my case, the optimal (financial) plan would be to sufficiently charge the batteries overnight to meet the house load for the upcoming day and export all solar energy.

Think you are half right. The optimal plan will be to run off grid in the overnight cheap period, charge your batteries sufficiently to get you through to the start of the solar day PLUS charge enough to meet your house load for the evening when the sun goes down.
Then during the day the optimal is to freeze export your AIO's so that no further charging goes into the battery.

However, it is my understanding that solar energy will always be used to meet house load in the first instance, and any excess solar energy can then be exported (or used to charge the battery).

You are correct, solar energy will be converted from DC to AC by your solar inverter, and then the excess goes into the batteries (but not if in export freeze mode) or is exported.

In my case, would you expect Predbat to manage the system such that solar energy used as house load will automatically be exported as well? If so, then I will be very happy indeed and I won't need to make any changes! If not, that's why I'm looking to manually export that quantity of solar energy which was used as house load (~2,500 kWh/annum in my case, so hence why it's important to me).

This is the crux of your idea. I get it now, you want to export to the grid the same AMOUNT of energy that your house consumed from solar generated during the day. That energy will actually come from your batteries, which in turn needs Predbat to have charged the batteries overnight the previous night an additional amount of the predicted house load during the solar day, so that it can then be exported the next evening.
[and the amount charged would need to be increased to allow for conversion losses in/out of the battery]

Its a great concept, and I get it, but no, Predbat isn't that clever. (at the moment, never say never and all that)

Trying to think of how you could do this with a minimal automation to surround predbat.

Something along the lines of:

• before the overnight cheap rate period
• calculate the kWh of house load during the solar day. You have sunrise/sunset times from the sun.sun entity in HA and predicted house load in predbat.best_load_energy, so you'd need to extract the load for the requisite time period
• increase that house load by your battery charge and discharge loss factors
• set input_number.predbat_set_reserve_min to that house load figure + 4% - that will ensure that predbat charges the battery with at least that reserve, plus what is needed during the early morning/evening

and a second automation (or could be combined with the first):

• calculate the kWh of house load that actually occurred during the solar day. Might be able to get this from one of the predbat load today sensors, or else, a couple of automations triggered at sunrise and sunset to take a copy/snapshot of the load_today sensor so you can subtract one from the other
• turn off export_freeze_only
• reduce set_reserve_min by the kWh load actually consumed (min 4%)

Something like this I think should work ....

[AberDino]

Thanks @gcoan for the clarifications and suggestions. I like the idea of using the input_number.predbat_set_reserve_min parameter to ensure the battery charges sufficiently and to subsequently manage the export process. Food for thought! I'll report back at some point once I have a working solution (or have another question).