Positive watts from Grid when sufficient solar

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duncangardiner asked Aug 31, '23

Positive watts from Grid when sufficient solar

Hi I have a new Victron system online, with RosenPV batteries (PylonTech LifePO4 clones) and Solar panels.

I am working through the initial configuration niggles where I have set things incorrectly/naively and slowly getting the system optimised.

One challenge I am noticing is that (we are grid connected to mainly push excess energy to the Grid, and only want to pull energy from the grid at specific times - at night when needed). That even when we have sufficient Battery to top up our morning PV production, VRM is showing small amounts of energy being drawn from our Grid connection:

This happens at both ends of the day when the PV production falls below the Load usage (we have no grid side loads, all are on the critical circuit).

So my question is: Have I missed a setting in the MultiPlus/ESS assistant within the MulitPlus that is now allowing the Grid to push energy to us even when we do not want it. Or is some leakage from the grid, common and just a factor of being Grid connected?

Kind regards

Duncan

Multiplus-II grid ess settings

grid-leakage.jpg (171.2 KiB)

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Answer 1 · 2023-08-31T08:14:03Z

seb71 answered · Aug 31, 2023 at 08:14 AM

List all your components and how are they connected.

What is your Grid setpoint in ESS?

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duncangardiner commented · Aug 31, 2023 at 10:15 AM

Hi @Seb71

I have:

2 x solar arrays, of 9 panels and then 4 panels, all 550w at 13.11A so a total of 7150w max
Connected via a DC duel channel combiner box to a Victron MPPT RS 450/100 TR Charge controller.
I then have a Victron MultiPlus II 48V 8000w inverter charger, which controls the inverting and Grid forwarding or charging from the Grid.
Sitting over the top of the charge controller and MultiPlus inverter is a Victron Cebro GX
Between the MultiPlus and the Charge Controller via a Lynx 1000 busbar are 2 RosenPV 48v 200Amp batteries.
I have no Victron shunt nor BMS. Instead relay upon the RosenPV batteries internal BMS which is a Pylontech clone.

My Grid setting in the ESS assistant on the MultiPlus are generic, because Portugal (where this system resides) is not a Victron supported country and therefore has no Grid profile prebuilt.

The ESS Setpoint within the Cebro GX is currently set at :

Kind regards

Duncan

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ess-set-point.jpg (118.2 KiB)

seb71 duncangardiner commented · Aug 31, 2023 at 12:19 PM

nickdb already answered about the Grid setpoint.

If most of the time you see 50W from grid, it's expected. Lowering the Grid setpoint value will lower the power constantly drawn from the grid, but it will also increase the chances to occasionally feed in some power. You can test with different values to see what's best for your system and usage.

I noticed your Active minimum SOC is 10%. For an ESS system, where grid is available, I would not discharge the battery that low (to extend its life). Also you risk having very little battery during a grid failure if you actually discharge it that low most of the time and it happens at the wrong moment.

Make sure that the ESS dynamic cut-off voltages are also set appropriately.

Since you say that your batteries are Pylontech clones, you could follow that guide.

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Answer 2 · 2023-08-31T10:40:12Z

nickdb answered · Aug 31, 2023 at 10:40 AM

That is normal in an ESS. Power ebs and flows around the grid setpoint. You can drop the 50W and find an optimal point that pulls less, mine sits at 10W.

You will never be net 0 with ESS as when loads transition there is power that must be sunk or pulled from grid.

Where not feeding back, some just drop mains until needed.

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duncangardiner commented · Aug 31, 2023 at 10:56 AM

@nickdb thanks for that, I thought this might be the case. It is a bit annoying from my point of view that like now:

I am producing 10 times my AC loads of PV production, but most of that is going into charging my Batteries, and the Grid is still a positive draw, rather than a negative or neutral position. I'd rather have the Grid at zero or being negative (pushing a constraint 10w) and then force the Battery charging to fluctuate up and down from the excess, being the total PV production minus the AC loads.

I was hoping to be able to set better priorities that allowed me to keep the Grid usage to only those periods I want to draw from. Specifically at night when power is cheaper here.

I guess a bit more research and looking at the Victron configuration to see what influence I can impart on my settings.

Kind regards

Duncan

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ess-setpoint-at-10w.jpg (164.1 KiB)

seb71 duncangardiner commented · Aug 31, 2023 at 12:24 PM

I'd rather have the Grid at zero or being negative (pushing a constraint 10w)

Check with your power company if they charge you for power fed into the grid. In some places they do.

and then force the Battery charging to fluctuate up and down from the excess

When the battery is full, you can't force current into it (unless you also rise the voltage to unsafe levels).

The grid is a good buffer for quick changes of the loads (big loads turned on or off).

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