Clipping Buffer (hybrid inverter)

[rholligan]

Is your feature request related to a problem? Please describe.
I currently experience clipping when solar generation exceeds inverter AC capacity, and there is no or limited battery capacity to make use of inverter DC capacity.

Describe the solution you'd like
It would be great to see additional features designed around preventing clipping. Predbat does already attempt to accommodate clipping within the plan, however is closely optimised according to solar forecast and low / negative import rates (as intended!), which can come at the cost of reduced flexibility when e.g. battery is charged, and solar generation exceeds forecast rates. This is particularly evident in summer since the solar forecast looks at average generation across each hour, but in reality there could be peak generation for 10 minutes while there is a break in clouds, then 10 minutes of cloud cover etc.

The feature could work by allocating some overhead / buffer in the battery to accommodate clipping, especially during summer / peak generation months. The buffer should be active during period where generation is set to exceed inverter capacity. Once risk of clipping is over, the battery should revert to regular target SOC (e.g. 100%). The start / end time and amount of spare capacity could be determined based on e.g.:

1. Manual user setting
2. Ratio of import to export rate (e.g. allocate a higher buffer when export rate is significantly greater than import)
3. Sunset / sunrise times, plus an offset

Additionally, battery charge power should be set to maximum throughout this period, and priority given to exporting generation (battery is only charged at the minimum rate which avoids clipping).

Describe alternatives you've considered
I currently run an automation which triggers manual discharge earlier in the day to create this buffer capacity within the battery.

Additional context
Add any other context or screenshots about the feature request here.

[gcoan]

As an alternative solution to reduce clipping, could either make the battery charge rate an externally controllable entity (so could manage via an automation), or (preferable), predbat plans the charging at a rate such that solar charging is spread out over a much longer period rather than always charging at max rate.

Tomorrow being a good example (ignoring the zero rate import period mid day), there is loads of solar forecast and so the batteries (drained down overnight) will be fully charged by 11:00. Thereafter solar will be exported, but risks clipping.

If the battery was charged lower and slower over a longer period of the day it would reduce the risk of clipping as its charging and exporting for longer

[rholligan]

As an alternative solution to reduce clipping, could either make the battery charge rate an externally controllable entity (so could manage via an automation), or (preferable), predbat plans the charging at a rate such that solar charging is spread out over a much longer period rather than always charging at max rate.

Tomorrow being a good example (ignoring the zero rate import period mid day), there is loads of solar forecast and so the batteries (drained down overnight) will be fully charged by 11:00. Thereafter solar will be exported, but risks clipping.

If the battery was charged lower and slower over a longer period of the day it would reduce the risk of clipping as its charging and exporting for longer

I would actually avoid using charge / power limits during periods where clipping is likely, since these can inadvertently result in clipping also. However, the same effect could be achieved by setting lower SOC targets (solving for clipping buffer), and prioritising all generation to export (battery is only charged at the minimum rate which avoids clipping).

[PatrickJanssens]

I think the key is to have the battery SOC as low as possible prior to the time clipping is expected (I set it to 10%). As soon as clipping is happening I set an automation to switch off the Eco mode and set the system to Timed Discharge, still with a low battery discharge SOC (this can be done either based on the Solcast forecast, or based on the actual PV production). This way the Excess PV is sent to the battery, but when PV production drops below the inverter capacity the battery is discharging again to increase the buffer for more excess PV. I don't think there is a need to adjust the battery charge rate, as long as it can be configured to only send the excess PV to the battery (seems to work fine on my GivEnergy hybrid inverter using timed discharge). The limiting factor is really the battery capacity, so key is to start with an as low as possible battery SOC, and ensure it can discharge to the grid when no clipping is occuring to make space for more excess PV.
In order to ensure I have a full battery when the sun sets I set my system to revert back to eco mode and disable the discharge schedule once the remaining PV foreceast drops below a certain value (I presently set it to 12 to 15 kWh). This way I'm sure to have a full battery when the sun sets.

Looks something like this (though set charge level to 75% to cover evening loads and set an intermediate timed discharge SOC at 50%):

[springfall2008]

I've been trying to fix this by fixing the model for clipping, a new version is being tested on main

[rholligan]

Sounds good to me!

[rholligan]

Hi Trefor, clipping prevention is working well in the background now based on forecast PV and inverter limits - thanks for the efforts on that.

Is there any appetite to add further user control around this feature? In an ideal world I'd be able to adjust clipping prevention, especially during the Scottish summers where there can be rather unpredictable bouts of cloud and sun which may not prevent clipping when relying on forecast generation alone.

[gcoan]

Hi Trefor, clipping prevention is working well in the background now based on forecast PV and inverter limits - thanks for the efforts on that.

For me I'm unfortunately not seeing any sign of clipping prevention happening in my plan. Predbat pretty much always tries to charge the battery to 100% overnight (depending on rates of course), and never leaves any spare capacity for solar charging that would otherwise be clipped.

I think the problem is that whilst I can define my two inverter limits in apps.yaml, Predbat only has a total solar forecast. It could retrieve the individual sites from Solcast but would then need a sites to inverter mapping (I have Solcast sites for East and West arrays but the panels are spread over the two inverters). I don't think without an awful lot more configuration options this is solvable in a fully automatic way in Predbat.

What I have been doing in the summer is setting Predbat to read only part way through the night to stop the batteries charging fully and then setting the inverter charge rates to a much lower value so the batteries trickle fill through the day rather than charge at max rate. Automating this is I think more viable

[PatrickJanssens]

I don't feel clipping is captured well by PredBat. The solar forecast are not accurate enough to capture actual peak loads, especially on day with scattered clouds. I presume solcast averages out the peaks so have frequently experienced the battery to be full when "unpredicted" sunshine appears. For me personally I have implemented an automation that discharges the battery in the morning to ensure there is sufficient battery capacity available for clipping. My target is to discharge to close to 15% of my battery capacity, so I still have some battery charge available for sudden loss of PV or sudden high loads. This automation is triggered by the overal solar production forecast for the day, meaning if the solar forecast is low I keep the battery charged, Towards the end of the day I stop discharging the battery, triggered by the remaining solar production forecast for the day to ensure I have sufficient battery charge to cover the evening. This has worked quite well for me. I have been playing around with the settings for these two values. Right now I have set the values to 25 kWh for the full day forecast and 12 kWh for the remaining PV forecast. That works quite well for me and I have managed to capture most of the excess clipping since I implemented this. Some examples below:

A perfect sunny day:

(Note I recovered some 65% battery charge from excess solar)

Scattered clouds day:

Cloudy day:

Note that I am on the Octopus Intelligent Go tarrif, so I do not worry about the price paid for my solar production, and I want to maximise the use of the cheap overnight tarriff. But I'm sure there room to optimise this further, especially for those on other tarriffs. Key for me would be to base the required buffer capacity for clipping on more conservative (in this case high) peak solar predictions.

[rholligan]

The solar forecast are not accurate enough to capture actual peak loads, especially on day with scattered clouds. I presume solcast averages out the peaks so have frequently experienced the battery to be full when "unpredicted" sunshine appears.

This is exactly the issue I face as well.

What I have been doing in the summer is setting Predbat to read only part way through the night to stop the batteries charging fully and then setting the inverter charge rates to a much lower value so the batteries trickle fill through the day rather than charge at max rate. Automating this is I think more viable

While I don't have a dual inverter setup, I appreciate the sentiment to avoid an overly complex solutionby mapping sites to inverters. It sounds like addition of a "clipping buffer" could help to simplify things for you here as well. It sounds like having some degree of control over this clipping prevention would be important to you, to help tackle the more complex dual inverter setup.

These examples demonstrate that the current functionality of predbat could be greatly enhanced with the additional of a "clipping buffer" (delibreately reserving spare battery capacity in predbat plan) during the periods where generation may exceed inverter capacity. This would give the flexibility to accommodate peak loads, while optimising the overall plan in the normal way based on generation, usage, rates etc.

[gcoan]

It sounds like addition of a "clipping buffer" could help to simplify things for you here as well. It sounds like having some degree of control over this clipping prevention would be important to you, to help tackle the more complex dual inverter setup.

Yes it would be useful, in effect I am creating my own "clipping buffer" in the battery by only letting the batteries charge partially overnight.

I think to be a complete solution there's several additional components I'd like to see within Predbat:

1. A configurable "clipping buffer" per inverter with the size of the buffer being user defined either as a fixed number or as a helper entity that I could control via an automation depending on solar forecast

2. Ability to vary the charging rate dynamically per inverter. At the moment (apart from overnight slow charging when switch.predbat_set_charge_low_power is turned on) Predbat uses either the inverter max rate, or an over-ride figure in apps.yaml, but you can't set a helper entity name in apps.yaml. If you could then programmatically you could set whether Predbat is to charge at max rate or trickle charge during the day.

3. Linked to 2, when the charging rate is set to zero, the battery pause mode is set to PauseCharging. This is needed to get around inverters/firmwares that continue to charge at a slow rate when the charge rate is set to zero.

What I would anticipate is something like:

Overnight, charge rate is set to maximum so normal grid charging & discharging. Clipping buffer set to (say) 2kWh so Predbat leaves 2kWh spare capacity in the battery. Normal predbat optimisation of charge and discharge periods so that the battery gets charged overnight at the cheapest rates.

Sunrise, my automation sets the charge rate helper entity to zero. Predbat sets inverter charge rate to zero and enables PauseCharge mode on the battery.

From sunrise to say 10am, all solar is exported.

At 10am, my automation sets the charge rate helper entity to 900W. Predbat sets the inverter charge rate to 900W and disables PauseCharge mode. The battery starts charging at 900W, this slow charge reduces the chance of clipping occurring through the solar peak.

At 3pm, my automation sets the charge rate helper entity to the inverter max rate, Predbat mirrors that on the inverter.

I have two inverters one of which is East facing and one of which is East and West facing so I would follow the above timings for inverter 1, but for inverter 2 I wouldn't start the trickle charging until about 1pm as the peak for that array is later.

If you are using the Solcast integration, the latest versions includes the site (array) specific breakdown of peak solar times in the peak time Solcast sensor so these can be easily used in an automation. Taking account of either the estimate or estimate10 times if you wish to:

[rholligan]

Hi Trefor, any thoughts on adding capabilities to adjust handling of clipping?

It's a sunny day with clouds here today meaning I'm often generating higher peak power than forecast, and with a lot of negative slots early this morning, my plan has resulted in battery being full over mid day / peak generation period resulting in clipping.

It would have been great to have some control over this, to avoid the clipping.

[springfall2008]

The cloud model should handle this, it just depends on your skew between the 10% and average scenario.

As this ticket is old I'm going to close it, please re-open if the issue is there on latest.