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somc

We had a new 10KWp PV system installed a month ago. I am puzzled as to why the total output shown on the inverter display is higher than on the generation meter. The figures after one month are widening and today are


Inverter 229KWH


Generation meter 187KWH


Could it be that the inverter gives the output before it converts it to AC and the difference is a measure of the inverters efficiency





OSHpvgen

It is very common for the 2 figures to be different.


It is most common for the inverter to be higher than the generation meter.


Most often this is simply due to cabling losses between inverter (in the loft?) and the generation meter (in the cupboard under the stairs?).  The further the distance, the more the loss.


If the distance between inverter and generation meter is quite short then the obvious thing to check is that the cable is the right size.  Too small and greater losses will occur.


Other possibilities exist. Generally speaking Inverters are less accurate than Generation Meters (?!?!).


Unfortunately FiTs payments must be based on the Generation Meter reading.





SteveRogers
My SMA inverter also records higher output than the meter but only by 1 or 2 kWh per month at most.

Steve
URN215

PS Please, Sheffield, can we stop the spam posts like the one above from Massyers?
bhommels
Hi All, The SMA manual states that the on-board meter is not calibrated. The generation meter is, so that would explain the difference. In my case, the SMA SB3000HF inverter reads 2-3% lower than the generation meter.
Bart
SteveRogers
bhommels
the on-board meter is not calibrated. The generation meter is, so that would explain the difference.

But the difference surely should not be as large as the original post by somc above. I'm wondering if the generation meter should be checked in this case.

It seems a big discrepancy to be explain by cable losses alone. OTOH, 10kWp is a big system so maybe there is a big current on the AC side (though the installer should have taken that into account with the diameter of the cabling).

Steve
rodney1evans@btinternet.com
I have a rooftop array that is 3.75kw and is just over 5 years old. The inverter which is an Aurora1 has started to malfunction, it blinks and then switches to alarm mode. The whole process is then repeated. Shouldn't an inverter last longer than that and does anyone know how to fix it or anyone in the Oxford area who can carry out a repair. The output is down by 75%.
pnews99@hotmail.co.uk
check the fault leds on the display , it may be a panel fault or just a faullty fan, does it not have a 10 year warranty
BackYardSolar
I have found that the Solar PV installers don't actually understand the importance of the cable sizes. Most were electricians that swapped over to solar PV and think that the voltage drop or loss is 5% as in a house ring main.

However this is not the case as it is only 3% on the DC side to the inverter, but most use a 4mm cable as a one size fits all systems approach which is wrong and should always be calculated.

Worse the inverter to grid connection should be less than 1% how many MCS approved installers know that??

A normal 4kWh (16A max) system with a inverter in the loft and greater than 15M away from the grid connection point probably needs a 6mm grid connection as the losses exist not only in the cable but also in the mains isolators, export meter and breaker.

The cable rating means nothing, it is the cable rating over the distance and ventilation conditions that count.
rodney1evans@btinternet.com
pnews99@hotmail.co.uk
check the fault leds on the display , it may be a panel fault or just a faullty fan, does it not have a 10 year warranty

It does have a ten year warranty but I have received no response from the installer or supplier nor the manufacturer so far (no surprise). I expect the same from the insurer. I will check the items you mention, but I will be going blind as you can imagine.
Thanks for your reply.

RE
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