ESS Minimum SoC limitation

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pleriche asked Feb 2, '22

ESS Minimum SoC limitation

First, the scenario: With rotational power cuts ("loadshedding") upon us again here in South Africa I have set my Minimum SoC in the ESS menu to 40%. This leaves me enough battery reserve to endure the worst overnight loadshedding I've experienced so far.

The issue I have is that the Multi will always recharge the batteries from the grid if the SoC falls below 40%. This costs me money, often unnecessarily, because tomorrow the sun will recharge my batteries for free. I want it to only recharge from the grid once the battery level falls critically low, say 15% SoC.

Effectively, I want ESS to manage my battery SoC levels as follows:

Below 15% SoC: Do not discharge the batteries if the grid is available. Charge the batteries from the grid, if available.
Between 15% and 40% SoC: Do not discharge the batteries if the grid is available. Do not recharge from the grid.
Above 40% SoC: Freely discharge the batteries regardless of whether the grid is available or not.

This doesn't seem possible without resorting to hackery, or am I missing something? Consider this a feature request if my assessment is accurate.

Edit:

A way to overcome this limitation would be a Maximum SoC for Grid Charging option in the ESS menu (with a default of 100%). I could set it to 15% to achieve my goal of only charging from the grid when the battery level has fallen critically low.

Note that this option should not disable the charger in the Multi entirely, since excess power from AC coupled PV should always be utilized to charge the batteries.

ESS SOC

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Marco Nijholt commented · Feb 08, 2022 at 12:05 PM

This exactly what i was expecting this system to do when i purchased it, hope it comes with an update!

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Answer 1 · 2022-02-02T10:43:17Z

Mark Maritz answered · Feb 02, 2022 at 10:43 AM

This will help alot!

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Answer 2 · 2022-02-02T10:46:24Z

nickdb answered · Feb 02, 2022 at 10:46 AM

You can use ESS schedules to prevent battery discharge and to limit when it will charge from grid and at what percentage it will cease topping up.

Works reasonably well.

https://www.victronenergy.com/media/pg/Energy_Storage_System/en/configuration.html#UUID-eea56ee5-efe2-0fce-ab6f-ba51656dfb45

With a sufficiently sized battery, it's not a problem I run into much, except on really poor PV days, in which case going to grid is required regardless. The probability of running below an already low minimum SOC is rare.

It's more practical to design your capacity to run fully off battery, at which point load shedding is irrelevant.

It only becomes an issue with a "hybrid" design which is part backup part solar, then you are stuck in the grey area of managing usage, something Victron didn't really design the system for.

Given the large footprint in SA, it would be nice to augment the system to have a more flexible/customisable ESS without needing to re-dev the product or get creative with nodered etc.

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pleriche commented · Feb 02, 2022 at 11:17 AM

You can use ESS schedules to prevent battery discharge and to limit when it will charge from grid and at what percentage it will cease topping up.

My biggest issue with scheduled charging is that it blocks discharge regardless of SoC. For example, if I have the target SoC of 40% set on the schedule then it will not discharge the battery even if it is at 100% (while the schedule is active.)

It's more practical to design your capacity to run fully off battery, at which point load shedding is irrelevant.

Sizing the battery for the worst case scenario is not a good investment if a grid connection is available most of the time. I have sized my battery to carry me through most summer nights, and only barely.

It is rare for loadshedding to be longer that 2.5 hours per night, so I just need to build in enough margin in the minimum SoC to carry the loads for that duration. My gripe is that I do not want to pay for grid power to recharge to the minimum SoC once the grid returns - the sun does that for free.

Given the large footprint in SA, it would be nice to augment the system to have a more flexible/customisable ESS without needing to re-dev the product or get creative with nodered etc.

Can't agree more.

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nickdb ♦♦ pleriche commented · Feb 02, 2022 at 11:27 AM

Given the forecast 20% increases, compounded and pending 4-quadrant billing, The ROI on battery upgrades was under 6 years for me, peace of mind - priceless.

In this area it's not loadshedding that is the issue, it's the subsequent transformer trips and cable faults which extend the outage.

The last record was 3 days but varies anywhere from 8 hours to 24.

The longer load-shedding continues (and we're in for it big time over the next 200 days + while the nuclear plant is refuelled and maintained) the more faults occur and the longer the response times to resolve.

There has been a big trend to up battery capacity to deal with this, and the increasing costs make it a no brainer.

Nonetheless, a more flexible ESS would go a long way to giving victron a compelling local market advantage.

psssst @mvader (Victron Energy) your SA clients are calling ;)

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Answer 3 · 2022-02-02T11:20:41Z

Jaco Reinecke answered · Feb 02, 2022 at 11:20 AM

Yes, please!

Although scheduled charging is there, it is not what it was intended for.

Auto Grid Recharge option, based on SOC levels users want to set it at.

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Answer 4 · 2022-02-02T11:26:09Z

Alexandra answered · Feb 02, 2022 at 11:26 AM

@pleriche

I have not tried this myself in this application, but there is a way to program the Aux relay to disable the internal charger using the charge current control assistant.

Using state of charge to add the conditions maybe use a bmv relay if you have one in the system, or maybe the gx generator menu. Or just a switch to give it a signal manually operated by the user to signal the Aux to trigger the assistant.

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pleriche commented · Feb 02, 2022 at 01:49 PM

That is a interesting idea. Would it be possible to make this work with AC coupled PV? I still want the charger in the multi to charge the batteries from excess PV, it should just not charge from the grid when the SoC is above a certain level.

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Answer 5 · 2022-02-02T11:36:56Z

Louis van der Walt answered · Feb 02, 2022 at 11:36 AM

Yes I would like this. It will give me the option to tell the system You can recharge from PV but not the grid after there was a grid failure.

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Ingo commented · Feb 02, 2022 at 12:01 PM

@Louis van der Walt I haven't checked for a long time but I think I use the Charge Control Assistant to set my charge current to 1A for the first 20 minutes after the grid return. I seem to recall that this does NOT affect the PV charging but there was mention on the 2.80 release notes that this behavior will change to also drop the PV charge current. For me this is a No-No going to 2.80 as the original behavior work great for me. I will see if there is a workaround at some point in time.

Edit: Just to clarify, I am talking bout MPPT's and not AC coupled PV which you might refer to.

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ESS Minimum SoC limitation

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