ESS Minimum SOC Setting unexpected behaviour

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dr-t asked May 15, '24

ESS Minimum SOC Setting unexpected behaviour

I have my Quattros and Cerbo set up in an ESS configuration. During the solar storms, I manually disconnected grid power. I set up the ESS "Minimum SOC (unless grid fails)" setting to 20%. I also set up the generator to automatically start if battery SOC reached 15% and for the generator to stop if battery SOC reaches 30%.

On one of the days, the battery SOC fell to under 20%. At that point, the essential loads were disconnected, i.e. the Quattros were not supplying any power. So the "Minimum SOC (unless grid fails)" setting behaved more like "Minimum SOC (even if grid fails)". The generator, however, did not start, because the SOC did not fall as low as 15%.

Thankfully, I have a UPS at the output stage and I noticed after about 1.5 hours that I was being supplied by the UPS. At that point, the battery SOC was 18.5% or so. I do not know why the batteries dropped to 18.5% during those 1.5 hours - maybe supplying my Victron equipment? I manually started the generator to recharge the batteries.

Why did this happen? Is there any other setting I should be looking out for?

My load was about 3kW at the time and I have two Quattros wired in parallel capable of supplying 30kW on the inverter output, so there was no possibility of an overload.

Thank you.

ESS

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Answer 1 · 2024-05-15T13:40:31Z

Alexandra answered · May 15 at 01:40 PM

@dr_t

ESS and all its settings only work when grid is connected. You removed that when you manually disconnected the grid. Not it cant ess.

Minimum SOC is the level the battery will discharge to when grid is connected otherwise it is actually inverting. So that's an entirely different setup now.

If you have the inverters to shut down at a voltage or soc then that is the setting to check when there is no grid. That is on the inverter tab in settings.

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Answer 2 · 2024-05-15T20:55:12Z

Thank you, that's very useful.

By "inverter" setting you mean in the section "PV Inverters"? I don't have any such inverters, just the two Quattros.

I don't understand why the ESS settings don't apply if the grid is not present. The "Minimum SOC (unless grid fails)" setting states that it applies unless grid fails. That seems to me to imply that batteries will provide power if the grid fails even if SOC falls below this setting. The Victron system has no way of knowing that I manually disconnected the grid. I simply switched off the main utility circuit breaker - as far as Victron equipment can tell, there is no difference between that and the grid "failing".

I used to have the system set up in another mode (i.e. not ESS). However, when I explained my requirements to my dealer, he said I needed ESS, and set up ESS for me. He said my requirements could not be met in the other mode. I don't know why.

My requirements are: a) use solar power when available, b) use batteries when not (or to top solar power up), c) use the grid next, d) when none of those sources of energy is available, start the generator and run it at 75% of its PRP rating (exactly, or as near exactly as possible) to run my loads and charge up the batteries with the remaining power, until the batteries are sufficiently full. Then switch off the generator and return back to the normal order of supplying power. Never feed any power back to the grid.

In the summer, I hardly ever need the grid or the generator. Most days there is enough sunshine to generate 3x the amount of energy I need, if not indeed many times more. My system was sized up to generate enough solar power on most winter days. However, as the power station introduced its own significant overheads, on most winter days, I seem to generate about half the amount of energy I need using solar power. So in the summer, there is no point in being connected to the grid at all most of the time, and so I would like not to be connected to the grid except on the few summer days when it is exceptionally cloudy and/or rainy. In the winter, I probably want to be connected to the grid most if not all of the time.

My generator is 23kVA, my solar system is rated at 25kW (and will in fact generate 25kW on a sunny day), I have two 15kVA Quattros paralleled together, my average consumption before power station overheads was about 1.7kW and my consumption after the power station overheads is about 2.5kW.

Is there a mode other than ESS that's more appropriate for this setup? Or if not, is there a way to achieve what I want in ESS mode?

Thank you!

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