Inverter reading higher kwh than meter ???

Scobo · Apr 8, 2012

Our inverter is reading about 6% higher than the PV meter.
It shows we've generated 311kwh since installed whereas the meter only reads 290.
Is this normal ?
Im guessing it's probably due to cable/efficiency losses.

GaryM · Apr 8, 2012

Most inverter readings won't be accurate. Has yours not got a calibration menu where you can input a given percentage to bring the figures in line with the generation meter?
My Fronius IG TL 3.6 has this option. Without knowing for sure I reckon there's a possibility your Fronius IG30 has too.

EDIT - I don't think it has - Fronius International GmbH - Products - Grid-connected inverters

flyman · Apr 8, 2012

You may find that if you're using an Owl or similar as a guide to output, this is normal as CT's aren't 100% accurate. I have various monitors attached all vary in comparison to the pulse count from the export meter. I'd suggest that you might consider the display a guide rather than an accurate output.
A display that may be more accurate is Current Cost with the Optismart.

Scobo · Apr 8, 2012

flyman said:
You may find that if you're using an Owl or similar as a guide to output, this is normal as CT's aren't 100% accurate. I have various monitors attached all vary in comparison to the pulse count from the export meter. I'd suggest that you might consider the display a guide rather than an accurate output.
A display that may be more accurate is Current Cost with the Optismart.

No, I'm comparing the inverter reading with the generation meter.
As it happens, I am using an owl to upload to pvoutput.org using pvbeancounter which has a calibration option.
I've got it set to -5% so, after a bit of trial and error, the figures on pvoutput are now the same as the generation meter.
Just wondered if a 6% difference between the inverter and the generation meter meant there was a problem somewhere but I guess it's part down to the inaccuracy of the inverter and part due to system losses.

Gavin A · Apr 8, 2012

the difference sounds a bit high, but is probably a combination of differences in the tolerances between the meter and inverter - ie meter is reading a little high, inverter a little low, plus the cable losses.

We had a house we went back to recently a year down the line to find that the meter was actually reading higher than the inverter.

Mozzerr · Apr 9, 2012

Just for information:-
As of this evening, my SMA inverter says: 384.4 kwh total generation since day 1.
As does PVOutput.org (no fudging of the data coming straight from the inverter, so same figs to be expected.)
And my Landis & Gyr E110 "official" generation meter says: 384.7 kwh total generation (it was showing 0.2 when first installed - which was the figure supplied on the FIT application form to British Gas.)

Incidentally, my Owl current sensing meter seems to pretty much reflect the same instantaneous Kwp values as the inverter too... but I don't archive those values, just use the portable display for convenience more than anything.

Personally, I don't think I would be too happy with a 6% discrepancy.

HTH

confounded · Apr 9, 2012

The meters used are designed for the consumption market and not the generation market. We have had meters that are 20% behind the inverter. Initially we replaced everything we could having been told that the meters are never wrong by the manufacturer. We were even primed to swap the inverter out. The only way we were able to resolve it was to swap out the meter, which then tracked the inverter.

Having had this experience we recently sent an email to all our recent customers to make sure that their meter is roughly (2-3%) in line with their inverter before we hit the peak production season. We have had one customer come back with a 20% discrepancy. Our first action will be to swap out the meter. Sadly this will require a new MCS certificate and negotiations with the fit provider....

Mozzerr · Apr 9, 2012

My meter seems to be made specifically for Solar:-

Landis & Gyr - Landis and Gyr E110 5235 Solar PV Generation Meter

I would have thought that these things could be recalibrated, no? Seems rather a faff to have to re-certify...

flyman · Apr 9, 2012

This has prompted me to look in the loft.... 1.5kw system nearly a year old SAP2009 estimate 1232, Sunny Boy read 1289 and Elster reads 1316... just need to decide if I'm on a swing or roundabout now..

confounded · Apr 9, 2012

How do you recalibrate without sending back to the manufacturers?

Landis & Gyr E110 are one of the meters we use, my understanding is they are primarily used as consumption meter.

Scobo · Apr 9, 2012

Thanks for the replies guys.
Our meter reading is currently dead on the PV-SOL estimate we got so I don't think I'll bother getting the meter or inverter changed.
Sounds like it would be too much hassle.
Over the year, I reckon a 6% difference would only be about £60 in FIT payments anyway.

Scobo · Apr 9, 2012

Scobo said:
No, I'm comparing the inverter reading with the generation meter.
As it happens, I am using an owl to upload to pvoutput.org using pvbeancounter which has a calibration option.
I've got it set to -5% so, after a bit of trial and error, the figures on pvoutput are now the same as the generation meter.
Just wondered if a 6% difference between the inverter and the generation meter meant there was a problem somewhere but I guess it's part down to the inaccuracy of the inverter and part due to system losses.

Had a really cloudy day today and the PV meter is reading well lower than the owl so it looks like the owl is pretty inaccurate at lower wattages.
Going to try the Optismart to see if that's any better.

danesol · Apr 9, 2012

flyman said:
This has prompted me to look in the loft.... 1.5kw system nearly a year old SAP2009 estimate 1232, Sunny Boy read 1289 and Elster reads 1316... just need to decide if I'm on a swing or roundabout now..

We are the same the SB Inverter reads LESS than the actual Elster generation meter, so we arent going to complain :wink5:

Its out by 1.7units this year so far.....

empower · Apr 10, 2012

The inverter will usually read less than the meter in my experience. The meters are less affected from the harmonics created by large inverters, and the meter will be OFGEM approved for a class accuracy of 2 or 1 (i.e. 1 or 2% accurate) whereas the inverter reading will be less accurate.

SibertSolar · Apr 10, 2012

IEC 62053-21 Class 1 and Class 2 accuracy relates to the % tolerance (1% or 2%) of the base current (Ib)setting of the meter in question. Base current is typically 20A (so +/-200mA for Class 1) for most single-phase meters, but could be 5A, 10A or 15A.

As has been said, most inverters will differ in their readings from the kWh meter(s). 5-10% discrepancy is not unusual.

pvman · Apr 11, 2012

I thought the difference was due to the efficiency of the inverter and the meter reading on the inverter was calculated before the dc to ac conversion.

Tom

Scobo · Apr 12, 2012

Just to update, the Optismart came yesterday and the Envir display is reading 29 watts this morning whereas the owl is reading 185 watts so confirms my thoughts that the owl is way off at lower power generations.

esentinel · May 19, 2012

Hi, the problem I think is related to how the meter calculate the power.
I mean does it evaluate Vrms and Irms ? I know envy and Owl have the voltage set to a fixed value. This is the first problem of error. The second is, as you tell, at lower power caused also probably to the power factor that if not considered would put a big error.

Gerald Brady · Jan 31, 2021

I was concerned about a mismatch between my inverter and the generation meter. My sunnyboy remote meter agrees with the inverter and the generation meter is about 100kw behind them. This is over 10 and a bit years though (36,500 KW) so perhaps I shouldn't be worried. A 6% discrepancy sounds like something that needs looking at though.