Victron VRM energy measurements

Q&A and troubleshooting
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1

Hi everyone,

I have a question regarding the energy measurements given in VRM. In specific:

On a typical day - say Nov 17 - my installation generated 4.2kw of solar and consumed 2.4kw ac loads. Battery (4.8kwh) went from 39% to 61% in these 24h.

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Of the 4.2kw solar generated energy, 0.8kw where direct use, 3.4kw went to the battery. 3.4+08=4.2, it makes sense.

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Of the 2.4kw of ac loads, 0.8 kw are solar direct use, 1.6kw from the battery. 0.8+1.6=2.4, it makes sense.

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The battery should then have 3.4-1.6=1.8kw for charging. For a 4.8kwh battery, this represents 37.5%. Instead, the battery increased 61-39=22%, which represents a difference of nearly 40%, or 0.75kw!

Where does this energy go? Thanks for your help!

Marco

2

Heat mostly.

Example; The battery has charged 3.4kWh at let’s say 90% efficiency = 3.06kWh in the battery. Then discharged 1.6kWh to the loads at again 90% efficiency is about 1.78kWh from the battery. This leaves 1.28kWh in the battery, or about 26% charge in this example.

There is also standby loss, meaning the inverter will use power even when it’s not inverting.

3

Below is a picture of the installation

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It is not grid-tied, and connected to 2x arrays of 6x 470W solar panels.

Cheers!

Marco

4

The same applies. Efficiency does seem low for a multi RS.

Are you using the battery BMS for SOC?

5

Hello Mac,

thanks you for your replies.

I have a Pylontech US5000 battery, and am using its BMS to monitor the SOC. I have set it up according to the instructions given by Victron ( Victron & Pylontech UP2500, US2000, US3000, US2000C, US3000C, US5000, US5000B, UF5000, Pelio-L, UP5000, Phantom-S, Force-L1 & L2 [Victron Energy] )

Efficiency seems indeed very low, even considering heat loss. Assuming 90% charge/discharge efficiency as you suggested and inverter efficiency (rated 96%) there is still a good 10% energy loss unaccounted for…any ideas?

Thanks,

Marco

6

How long has it been since the battery was charged to 100% ?

7

Battery has reached 100% last times on the 21st and 22nd November…recently then…battery health is also 100%, it was installed in August this year. Whole system is pretty new…

8

The next step would be measuring what goes in and out the battery and comparing it with the BMS to see if it’s measurements are correct.