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ronski avatar image
ronski asked

VRM To Grid/From Grid kWh does not match my smart meter

I have Quattro 48/10000, it has the grid on AC in 1, and everything else on AC Out 1. So I have my incoming grid connection which goes through my smart meter then connects to AC in 1. All consumed energy is on AC out 1.

This means the Quattro is measuring power going to and from the grind, but the energy imported and exported as shown in the VRM does not match my smart meter data, I've only noticed this as I've added another battery and therefore import/export more each day.


 VRM from grid Smart Meter Import Difference VRM to grid Smart meter export Difference







Thursday 15 14.21 0.79 50 47.89 2.11
Friday 14.75 13.89 0.86 45 42.59 2.41
Saturday 14.96 14.27 0.69 48 46.16 1.84
Sunday 14.47 13.94 0.53 43 41.36 1.64
Monday 21.81 20.91 0.9 26 24.74 1.26
Tuesday 21.85 20.84 1.01 49 47.25 1.75
Wednesday 21.79 20.66 1.13 51 48.85 2.15


I can't find a way to get the exact VRM to grid value, so these are the rounded values that the VRM shows daily, but it still illustrates the point that the values are off.

Any idea what's causing this, surely the energy meter in the Quattro is not that inaccurate?

I am of course assuming my Smart meter is accurate - this was new a couple of months ago.

VRM
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4 Answers
hominidae avatar image
hominidae answered ·

...what device is actually measuring the data that gets pushed to VRM...assuming you have a GX and a grid meter installed? Is this a calibrated (MID) meter device?

Even a calibrated device (like your Smart Meter need to be) is not absolutely accurate. It has an allowed deviation of some percentage of the measured value and it can change with ambient conditions.

See: https://en.wikipedia.org/wiki/Electricity_meter#Accuracy ..and there are different rules in different countries.

Lets say that there is an allowed deviation of accuracy of 2.5% (note that this normally means a deviation of +/- 2.5% which gives a 5% range) and two calibrated devices are measuring the same value while either one is accurate at the other side of the allowed interval of the other, then readings between 97.5 and 102,5 (for the correct, absolute value of 100) are considered accurate.

That said, your table doesn't look too bad, does it?

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ronski avatar image
ronski answered ·

The Quattro is measuring the data.

I have an ET112 meter that measures the solar production of an AC connected inverter, over the course of a week that is pretty much spot on to what the official generation meter record's, so I was expecting the Quattro to be pretty accurate as well, but at roughly 1 kWh out over 20 kWh, which is 5%, it seems quite a bit, but if both were at either end of the tolerance limits then they would actually be within the tolerance limits.

UK meters have to be accurate between+2.5% to -3.5% throughout the entire load range at which the meter is designed to operate.

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hominidae avatar image hominidae commented ·

Right, I think I miscalculated the maths behind the 5% interval...changed it in my post above.

With the ET112, even if not an officially calibrated MID version, I tend to think, that all versions come from the same production line, hence having the same design and same parts (only the effort and fee for testing/calibration & official certification according to accuracy gets spared) and those non-MID versions are most likely as accurate as the MID versions.

However,, I think the Quattro is not calibrated and with the large power range that thing has, I think the accuracy is much lower, compared to a MID certified meter.

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Jason - UK avatar image
Jason - UK answered ·

@Ronski My system has the same discrepancies and that is normal for a Multiplus / Quattro as it uses a CT sensor and only measures kw whereas nearly all smart meters read kva & kW making them more accurate, and also they are MID compliant whereas the inverter CT sensor is not MID compliant. I wouldn't worry about it. The information is good enough and if you have a consistent discrepancy, then add or omit the difference when recording it manually.

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ronski avatar image
ronski answered ·

Thanks for the replies, I have easy access to the smart meter data, so it doesn't really matter.

It does seem to be reliably out every day, shame there isn't somewhere I could put an adjustment factor to at least get it closer.


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dansonamission avatar image dansonamission commented ·
Add an ET112 to the grid connection rather than using the inbuilt CT.
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hominidae avatar image hominidae commented ·

What is the system with/where you capture/store the data now?

...with easy access to the Smart Meter data, you could use Node-Red/IoBroker/a script on a RPi/NAS to apply the corrective factor to the data before sending it to your logger/database.



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