Accuracy of smart meter export reading?

[Paul Smith]

I've recently installed my own PV system using 8 x JA Solar 405w panels and a Solax dual mppt 3600w inverter. The panels are mounted on a frame on an outbuilding flat roof, everything has been done by myself with the exception of the grid connection which was carried out by a qualified electrician. I have sent off a G98 to my DNO which has been accepted but i'm not receiving any export payments as it's not MCS certified.

I have been monitoring my useage for a long time and I use 16Kwh per day, my monthly bills are always 480Kwh +/-10Kwh. My system went live on the 1st of September and during the month I used 300Kwh which is 10Kwh per day, a reduction of 6Kwh per day which is very pleasing, a saving of 180Kwh.

However something doesn't quite stack up. According to both my inverter and the generation meter I generated 255Kwh during the month which suggests that I exported 75Kwh. However my Shell Energy smart meter shows an export reading of 133Kwh, so it appears to have over read by 58Kwh??

Nothing else has changed so I wouldn't have used less than a "normal" month. Is it possible for the smart meter to over read the electricity exported?

Has anybody else seen this on their systems?

Thanks in advance

Paul

 

[Paul Smith]

Any thoughts?

 

[wattmatters]

Is it possible for the smart meter to over read the electricity exported?

Depending on where you are and the utility meter you have, sometimes older meters need to be reconfigured following a grid-tied solar PV installation to manage the export register correctly.

But in general, utility meters are usually good quality and will be correct.

My system went live on the 1st of September and during the month I used 300Kwh which is 10Kwh per day, a reduction of 6Kwh per day which is very pleasing, a saving of 180Kwh.

However something doesn't quite stack up. According to both my inverter and the generation meter I generated 255Kwh during the month which suggests that I exported 75Kwh. However my Shell Energy smart meter shows an export reading of 133Kwh, so it appears to have over read by 58Kwh??

Can you validate your production data? Does your utility provide daily (or interval data) you can compare with your own.

Is 255 kWh a reasonable yield for your PV array for your location and array configuration (and weather)?

That's an average of 8.5 kWh/day and 2.62 kWh per kW of PV.

End of the day, from a billing perspective it's the utility meter that matters but it would be nice to have your own metering align.

Perhaps start to record daily values for a while to see what happens.

 

[XO4001]

Any t

You could buy the https://www.emporiaenergy.com/ and see what is what.

 

[Paul Smith]

Depending on where you are and the utility meter you have, sometimes older meters need to be reconfigured following a grid-tied solar PV installation to manage the export register correctly.

But in general, utility meters are usually good quality and will be correct.


Can you validate your production data? Does your utility provide daily (or interval data) you can compare with your own.

Is 255 kWh a reasonable yield for your PV array for your location and array configuration (and weather)?

That's an average of 8.5 kWh/day and 2.62 kWh per kW of PV.

End of the day, from a billing perspective it's the utility meter that matters but it would be nice to have your own metering align.

Perhaps start to record daily values for a while to see what happens.

I record the readings every day, the inverter reads the same as the consumption meter I fitted so I'm happy that my production figures are correct. My panels are due south with no shading so they're in a pretty good position.

It just seems odd that my household consumption has clearly dropped by 6Kw a day yet if I subtract my export reading from my generation reading the numbers don't tally.