Avoiding high idle consumption with DESS - potential work-around?

Q&A and troubleshooting DESS
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Hi everyone,

Problem:

I have a moderately sized DESS system consisting of 4x 10k Quattros, with AC coupled PV. I’ve noticed when DESS schedules the system to idle (grid-to-loads), the idle DC consumption on the system is close to ~500W (which aligns with some others on this forum). This is obviously quite high so I’ve spent a while trying to avoid this.

Another observation was the system goes into a deeper idle when DESS is disabled and SOC at ‘ESS minimum SOC’ (consuming closer to 100-150W from the grid, with DC consumption close to zero). I believe this is because the inverter/charger circuit is turned off, due to peak shaving also being disabled (if configured as such).

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Work-Around:

I set up a Node-RED automation that sets /Settings/CGwacs/MaxDischargePower to 0 (“Maximum Inverter Power” in Venus) when /DynamicEss/ReactiveStrategy is either 9 or 15 (the two seemingly relevant idle states). Otherwise it’s -1 (disabled).

I’ve verified this puts the system into the lower idle state, similar to as-if it were at ESS minimum SOC (it results in /Hub4/DisableFeedIn being set to 1)

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Question:

I’m still testing but was hoping for the wisdom of the crowd — anyone see potential problems with this?

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Add’l Background / Assumptions:

My utility offers a simple weekday on-peak (8 hour) / off-peak (16 hour) rate plan, and so most of the year my system is idling close to 12-14 hours during the night.. Selling back to the grid is not advantageous, but charging from the grid ahead of the peak hour can be.

  • When solar starts producing in the morning, I believe DESS will quickly change the ReactiveStrategy away from the two idle states above.
  • When DESS wants to self-consume, or charge from the grid, the ReactiveStrategy should also change.
  • If grid is lost, the system should back up as expected (5. Configuration)
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OK so close to 24 hours in and this simple strategy seems to be working great…

Prior to adding this automation, notice the idle draw and SOC decline overnight:

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Now, with the automation setting /Settings/CGwacs/MaxDischargePower to 0 when /DynamicEss/ReactiveStrategy is either 9 or 15 (scheduled idle):

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  • The current is basically zero and the SOC barely dropped.
  • There were a few blips in current draw as the BMS SOC slightly fluctuated overnight. I believe this caused DESS to self-consume briefly, to bring SOC back on plan (which is another good outcome, as the automation still allows DESS to do these fine adjustments).
  • System started self-consuming normally in the morning when PV started producing.

Given tomorrow is Monday I will see whether this still allows DESS to charge ahead of the peak period.

3

OK so another day with no problems! :slight_smile:

To understand why this works a bit better I dug into the Venus source. Here’s the idle() function DESS calls:

DESS sets MaxDischargePower to a minimum of 1, which seems to keep grid feed in active for DC PV (based on the comment). The work-around I suggest above overrides that with 0, which disables grid feed in.

So in my case with only AC PV, I don’t think there are any ill consequences. Those with DC PV may want to build some additional logic.