question

This apperntly bad DC efficiency also bothered me for a while. To check the VRM numbers, I captured all relevant mesuremwnts from the Venos OS, via Modbus, into a database.

From this data I can say the efficiency is much better than what the VRM data is showing. I have the strong suspicion that all the system loses are going into the VRM measurement “to Battery”.

But that is only true for the Venus OS version 2.x.

Since Venus OS 3.0 the VRM measurements “from Battery” and “to Battery” are matching with the data I captured. Now the losses seam to be added to the “Consumption” measurement.

I also see the same issue.

Therefore i am currently observing the issue, by integral calculating the BMS data.

So i can compare, what energy the BMS thinks goes in and out of the battery VS. what VRM thinks.

And there is a HUGE difference!!

for example i found out, that VRM does not count any engergy that is fed into grid from battery.

I usually have a lot of energy fed into grid from battery, as a i use a negative gridsetpoint of -150 to -300W, just to have minimal energy import from the grid.

so this is the data of the last ~30days:

As you can see... there is super big difference between VRM and BMS data...

Also i have data from my official grid meter, on which i get charged. So i consider this as the absolut correct value.

So...

VRM does miss 74,1kWh "into Grid"

On the other hand, VRM counts way too much energy into battery.

My assumption is, that VRM just adds this missing 74,1kWh to the "to Battery" value.

So, if i subtract these 74,1kWh from 405,7kWh, i get 331,6kWh, which is pretty close to the BMS calculated value of 327,3kWh.

And if i compare this with the 318,2kWh that the BMS thinks went out of the Battery, this would lead to 96,0-97,2% efficieny in/out of the Battery. This seems somehow realistic, isn´t it ?

But ultimately... VRM does count very wrong!!

Maybe someone from Victron can say something about this?

Maybe @Guy Stewart (Victron Community Manager) does know more about this?

additional information:

I did use Firmware V3.00-37 for capturing this data.

I will update now to latest "official" release of V3.00, and continue to observe

There is my example figures from the VRM for this year. I have beaten my batteries quite hard some days so inverters have been charging max current and therefore not optimal efficiency. System idea is also heat my workshop during winter with efficiency losses and at summer I use more optimal charge settings. I am happy with 90% charge and discharge figures :)

Please look your efficiency loss more closer as there is multiple steps when looking roundup efficiency.

has anyone else here checked the "to battery" vs "from battery" efficiency?

i would be interessted in your numbers, if you have an ESS and also feed into grid

When you are trying to work this out, you need to add the "to battery" from both the solar and the grid tabs in the dashboard.

You can then compare this to the "from battery" in the consumption tab.

On an ESS, mine equates to just on 20% losses, bearing in mind the built in metering isn't 100% accurate.

Also, the "to grid" usage in the solar tab, is not equated directly to PV or battery, so something may being lost there as the system unlikely tracks it down to that granularity.

The VRM numbers for "From Battery" and "To Battery" seem way off to me.

Here's what I have shown for this month so far:

And just for completeness the Overview and Grid too:

So I see 193kWh from vs 272kWh to, an apparent 71% efficiency. My ESS is set to about -30W setpoint so I avoid importing as much as possible, the grid is basically idle and has been all month.

However, I also have a BMV-712 and this shows completely different numbers from VRM. For same time period as above (I log all this to InfluxDB/Grafana so can pull out any time range at will) I'm seeing 251kWh into the battery (DIY LF280K stack), and 246kWh out. That's a far more palatable 98% efficiency.

Obviously the BMV figures are DC, it has nothing else to measure. I absolutely believe the BMV-712 figures, they're on par with what I'd expect. The VRM figures I'm guessing are perhaps showing AC figures, so after conversion losses both ways, which explains some of the loss of efficiency?

@Pedaaa an i talked about this wrong VRM-counting since a few weeks,

because i also got very bad/wrong batteryefficiencys.

it seems that VRM is definatly not counting energy that is pushed to the grid from battery.

if you just compare energy to battery with energy from battery, there is clearly a calculationproblem in VRM:

here an extreme example, with massive grid feed in from battery :

in june VRM tells me i used

100 kWh from battery and

290 kWh to battery.

-> 34,5 % efficiency

VRM says:

623 kWh feed in from solar, but

719 kWh feed in in the overview.

if i add (719 - 623 =) 96 kWh to the 100 kWh "from the battery", it looks more normal:

196 kWh from battery and

290 kWh to battery

-> 67,5 % efficiency

this is looking more real.