# question

## Big difference between from and to battery

If I look to my statistics in VRM on 30 days there is a big difference between how many power that comes from or go’s to the battery. In my opinion this difference can only be as large as my battery size.

setup: multiplus II go 48/5000 , 6 x Pylontech 2000 battery and a mppt 450/100

Consumption

Solar:

if you look at the from solar and direct use there are the same

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18 + 170 + 235 = 423. The total of the consumption for your system from the three sources.

The production number is your total produced the other three are the three sources it was metered out to. The solar to direct use should be the same as that is the figure that went direct to the loads in your house. (not passing through the battery). If i add those with a calculator there is a 1kwh difference but since it is rounded to the nearest kwh i think that will be why there is a difference. 241 + 250 + 235 = 726

The two battery figures being different are a combination of battery inefficiency due to heat and loses in charging and discharging and balancing uses. (When it gets near top charge and is charging and discharging the bank to top balance). These figures are reported by the pylontecs themselves if you have set up the comms.

It can be much larger than your bank size depending on how much you are drawing out your bank and cycling.

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I think there's more to this than just inefficiencies. You would have to have unmeasured dc loads or be actually exporting to grid from your battery to show such poor batt turnover. What does the System Overview tab show?

It could indeed be a bug in VRM. As an example, this is my System Overview..

Great efficiency hey! Alas no, I have Generator selected, and that (not Grid) shows in a box on the main screen, but not here. So I have no way to see cumulative Gen batt charge.

I know VRM has been under development and I'm not one to complain, but maybe now's the time. Or time for my mistake to be pointed out to me.. :)

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Here my system overview page, ik have no dc loads

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frederikbove ·

Ok, there's your imbalance. Granted there may be rounding, efficiency, and report-time errors, but I see 86 kWh missing.

It appears you have exported to grid up to 15 kWh (256 - 241) from the batteries. (You may want to investigate that). Leaving 71..

And if that 71 were to be attributed to unreported batt charge/discharge, and added to the 170 batt consumption, you'd get a round trip efficiency for the batts of (170+71)/250 = 96.4%. An at-best figure that doesn't allow for system losses, but way closer to expectations for Pylons.

The key to this is knowing which figure is calculated to make a balance. I think it's batt consumption.

Is it possible that at some point you've changed the 'Grid' setting in Venus to maybe 'Shore'? Then imports under that may have been squirrelled away and omitted from the reports.

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JohnC ♦ ·
It’s possible whit the Ess balancing that i send some power back to the grid but 71kwh on 250kwh is nearly 33% in my opinion that I have lost on 30 days whitch is a lot.

btW I have a ess system in my house always connected to the grid with a em24 grid meter. A friend of mine @Stijn Dhondt has nearly the same setup and is seeing the same phenomenon

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frederikbove ·
@frederikbove

I already found ~15 kWh exported, the 71 'unaccounted for'. I think it's import from the grid to the battery, and has remained unreported as battery usage because that figure may be derived by difference.

The EM24 might be a clue, but I've no experience with such. Would it be possible for you to reconcile your power utility account with these figures? No point if they use estimates, but if actual meter readings, then you could generate VRM figures from the exact dates and see where the difference lies. It's there, just gotta find it.. then determine whether a VRM or site issue.

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@frederikbove

Just some more input here.

Even in a keep batteries charged system, for power assist you will draw from the battery. the system will then replace it almost immediately, with losses .

The battery will go through float and absorption cycles, depending on how it it programmed and controlled by the battery itself. Naturally in a day the system for which I have attched figures for does this, the system raises the voltage from its float at 55.5v up to 56.2v which is its bulk/ absorption voltage (during ess operation with solar) and then it drops back down to the float again (this will not be classed as consumption but it is a consumer of power). So system 'losses'. Depending on how much heat your bank makes during this will also contribute to losses and be a consumer.

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I have the same issue with an EasySolar II-GX
522 in and 374 retrieved - A 30% loss is a lot more than one would expect

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or is it normal and my expectations were not realistic?

With such differences you would need to factor that in when considering the benefit of storing from the grid to reuse later during peak. Just to break even with a 30% loss you need peak price to be 50% higher.

Exemple if I buy and store 1,5kW to then only be able to consume 1kW it would need to be more than 1.5x and that's definitely not what my provider is offering.
Would be very much interested to hear from other experiences!

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Facing the same issue. (8x Pylontech US3000C, connected as 4x2 to the bus bar)

400 kWh to Battery this month.

And 289 from Battery.

Additional losses (beside regular efficency penalty) should be low, I have a constant temperature monitoring of the batteries and cablings and with around 28 - 30° in a 25-28° Environment, none indicates "huge losses" i'd say.

DC-Consumers - only a tiny microcontroller running the temperature sensors, neglectable.

What I did notice however is that the MPPT250 (I have a temperature sensor at the back) stays about 5° above room temperature, even during night. Could it be possible that the MPPT is constantly draining power from the batteries for whatever reason? (That is obviously not counted as consumption by the multiplus)

A second, MPPT 150, is also present, but did not yet add temperature sensors as it generally feels "colder".

Oh, and I have to "add", that this 5° difference is measured on the back, with 2 fans providing cooling. They turn of at 30°, which the MPPT never goes bellow.

So, actual Internal Temperature may be more like 35° or above - even if the Remote-Console says "State: Off"... ?

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