How to "read" PV panels,Meter and OWL

rolion

Hello,

Just started looking at the parameters of the system and ... i will need your help,again !

I have the PV panels,new digital esb meter and OWL installed.
According to the picture below,today I have used 14KWh and the PVs have generated 7KW with an export of 2KW.
Crossed & checked the ABB interface and is saying that i've generated 6KW today.

However,when checked the ESB meter,is black on white consumption of 12KW.

So,is the OWL not doing the work as it advertised,the meter is recording import/exports correctly or ... i am losing it here !?

Thanks.

You're not losing it what you are experiencing is the difference in calibration, electrical engineering design accuracy, differential calculations, maybe assumed values and quite possibly a touch of engineered optimism.

I take it the picture is a screen shot of the OWL meter readout?
Showing 6.7kWh PV input, a difference of +700Wh according to your grid tie inverter?

Ah where to begin...how nerd do you want it Rolion? Eff it ok full dork, here goes...

Photons hit the solar cells and are converted to Direct Current...this goes to your inverter which if they have a value in watts greater than the inverter self consumption they are useful power if they are a value less than your inverter self consumption your inverter becomes an appliance using energy not generating it (the ABB might see this and forget to mention it, the OWL will see this but read negative as positive). The difference between the power at the panel in DC and the power leaving the inverter in AC is the inverter efficiency...this is not ever in real life the same figure as the one quoted on the data sheet. While the one on the data sheet is true of a given load at a fixed temperature in perfect lab conditions (they aren't really lying either), in reality it's more of an exponential curve with peak inefficiency at low load and yes it can be negative depending on the design of the inverter.

So if your inverter read higher than your owl it is probably being liberal with the truth and giving you the panel power. However it's not so let's perhaps assume it's measuring the output power on the AC side same as your OWL. Now one has to ask how accurate is the ABB meter? Is it using a shunt (more accurate) or a current transformer (more cheap and cheerful), is it compensating for temperature induced resistance and reactive power? Is it output power or generated power before or after self consumption?

Next how accurate is the OWL? Usually these are current transformer jobs with that they are not at all precision instruments. Does it measure or assume the voltage to calculate Watts? What is it's specified accuracy? Does it compensate for reactive power?

The ESB meter you can be sure is a calibrated instrument and probably has a cert or one of them modren scany with yer phone camera linky jobs to a cal. cert.
It says you have imported 12kWh.
The owl disagrees saying you have used 13.9kWh - (6.7kWh - 2.2kWh) = 9.4kWh import.

You used 13.9kWh, 4.5kWh you generated on site, 2.2kWh you gave to the ESB for free and they sold to your neighbour.
Now we come to a discrepancy of 12kWh - 9.4kWh = 2.6kWh between what the ESB meter says you used and what your OWL says you have used.
21.6% disparity; something is not right. The metering system is outside of design spec.
Either it's the accuracy of the figures you quoted, the siting of your differential metering, the compounded inaccuracies in the system, the lack of discrimination between forward and reverse current or a combination of these faults.


My solution is buy a Fluke 17B+ (or a clamp on type like the 374 if you have a healthy reluctance for using series shunted meters on line voltage) with a calibration cert & verify every meter you use against it. I also rarely use the meters provided by the manufacturer of the equipment they meter because they more often than not have a bias or fudge factor and I always verify their fidelity.