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ruip avatar image
ruip asked

Measuring system losses in VRM

I’ve taken the following totals (kWh), from VRM from my last 290 days of operation:

(Rig: PV + Smartsolar 250/60 + Multiplus II 3000 + Venus GX + BYD 5,0kWh)


Total From = Total To = 12 130 kWh, so the losses must be "hidden" somewhere in here.

VRM reports 2016kWh charged to the Battery, but only 1325kWh discharged from the Battery. So, a 691 kWh loss.

Considering that the “From Grid” and “From PV” measurements are most certainly made before conversion losses [made, respectively, by the Carlo Gavazzi ET110 (in green) and SmartSolar MPPT (in blue)], am I correct to assume that this 691 kWh loss includes ALL inverter/charger losses, specifically:

  • Grid AC -> Battery [charger] <- implied in the VRM data
  • Battery -> AC Consumption [inverter] <- implied in the VRM data
  • PV -> AC Consumption [inverter] <- this one is not implied.

Can anyone confirm this?


Sanity checks:

  • The 1 325 kWh discharged from the battery are in line with the number of cycles I believe my battery has made (~1 cycle/day).
  • 691 kWh losses / [2 519 kWh PV Production + 939 kWh Grid to Battery] = 80% total efficiency, which seems in line with the literature.
Multiplus-IIVRM
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boekel avatar image boekel ♦ commented ·

Interesting! what kind of batteries do you have?

Also don't forget the standby ('no load') use of the system.

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ruip avatar image ruip boekel ♦ commented ·

I have a BYD B-PRO with 2 modules, therefore, a total of 5kWh.

I'm not sure, but I believe that the system consumption is accounted for (added) in the "Critical Loads". But probably the folks at Victron can share some knowledge on this.

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Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

There is some element of loss and inefficiency but I think a greater proportion is the known issue of BYD's high minimum threshold for power reporting.

Power use below 100W (for your 5 kWh) is not reported by the BYD, so it is not reported by the GX to VRM.

You are right that the Carlo meter is MUCH more accurate than all other meters in the system (Multi, BYD, MPPT, etc).

There is more documentation on this known issue here:

https://www.victronenergy.com/live/battery_compatibility:byd_b-box#known_issues

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nigelfxs avatar image nigelfxs commented ·

Many thanks for the link! I am experiencing the exact same low-power accuracy issue with the BlueNova BMS.

See topic https://community.victronenergy.com/questions/17636/possible-to-use-bmv-712-with-a-lifepo4-battery-wit.html

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