Panel generation vs Meter reading

C_Wormcake

Hi, Just a quick confirmation. I have a PV system installed which says the panels are generating, say, 10kwh in a day. My generation meter only registers approximately 50% of this. I expect it should read the same 10KWh, or marginally less. Am I correct?
The readings are at night when the battery has drained.
If I am correct does this indicate a faulty generation meter?
Thanks

QrizB

Honestly, it's impossible to be certain wthout a lot more info.

It's more likely that your generation meter is correct and the internal monitoring is wrong. Or they might both be correct but not measuring the same thing.

Netexporter

I wasn't clear what the exact situation is but if the difference is between the b=generation meter, which measures gross output from the panels, and what your smart meter is showing as exports, the difference will be your self-consumption. What goes into the battery is self-consumption, although that couls be complicated if you also force export to the grid from the battery.

QrizB

Further to Netexporter's message, the usual arrangement for a PV system like yours (assuming a hybrid inverter with a DC-coupled battery) would be:

Panels - inverter & battery - generation meter - consumer unit - smart meter - grid.

In this arrangement, the generation meter should be a bidirectional one that can measure in both directions and also give a "net" reading.

The inverter's internal measure of PV generation should not exceed the net reading on the generation meter, but the inverter isn't certified for metering and so can be a bit off.

The export register on the smart meter should be quite a bit less than the net reading on the generation meter.

C_Wormcake

Thanks to all of you. This is obviously a bit more convoluted than I imagined!

I have just changed from an invertor only system to a new inverter / battery system. The panels and generation meter are the originals. Prior to this change when I submitted my readings to EDF I was getting a message from them saying my reading was too low, I am not sure when the messages started but its possibly was when the Smart meter was installed. EDF suggested it was a fault in their system and nothing to worry about. My last submit was on the day of the new inverter install. The submissions are manual.

Initially when the original system went live the inverter figure was always slightly higher than than the generation meter. Over time the two drifted significantly apart, so it wasn't easy to keep track.

The new system is easier to monitor. There is an app. The panels are, as I said, showing a figure around 50% higher than the generation meter.

My understanding of the system is:
Panels - inverter & battery - generation meter - consumer unit - smart meter - grid.
The panels power the house through the inverter via the generation meter with any excess going into the battery but not via the generation meter.
Any further excess goes into the grid again via the inverter and generation meter.
This means all power so far is either in the battery, has been used or sent out via the generation meter.

If demand is too high for the panels power is drawn from the battery via the inverter and via the generation meter.
This should mean all power generated goes via the generation meter at some point. I can't see how the smart meter can be affecting the generation meter.

I am on the original FITS tariff so should be getting paid for all the power generated irrespective of consumption plus the deemed export amount. There is no balancing between in and out on the meter as far as I am aware. 
I do not use the smart meter for anything other than measuring the grid consumption. This is via Eon. The solar payments are from EDF.

Hopefully this clears things up.
Thanks everyone
Steve

QrizB

First things first. If you have added equipment (a battery) on the "panel" side of your generation meter (and from what you say, you have) then you absolutely have to tell EDF. They will almost certainly require you to get a MCS-accredited installer in to replace your generation meter with a bidirectional one. Until you do this you risk EDF cancelling your FIT.

I don't often use bold text but this is important.

Make sure the replacement meter is installed the correct way around otherwise you'll have problems.

See this thread here for an example of what can go wrong:

https://forums.moneysavingexpert.com/discussion/6621194/fit-meter-gives-strange-readings-installer-gone-bust/p1

Once the meter is replaced the problem might solve itself.

C_Wormcake

Hi, QrizB
Thanks for the info.
I was assured by the installers that as the generation level was not changing I would not need to inform anyone. Installers were GRCSolar.  
I will follow up with EDF.
Thanks

Martyn1981

C_Wormcake said:

Hi, QrizB
Thanks for the info.
I was assured by the installers that as the generation level was not changing I would not need to inform anyone. Installers were GRCSolar.  
I will follow up with EDF.
Thanks

Hi Steve, and welcome.

First off, QrizB is spot on. If the batts are on the DC side of the TGM, then if you charge them from the grid, and then discharge back, it would look like increased generation. So with DC side batts, you also have to replace the TGM with a bi-directional meter. This will clock units in both directions, and give a net figure.

It's the net figure that you will now have to forward to EDF.

[Totally, totally guessing here, but perhaps if the new inverter isn't a hybrid model that can take AC from the grid and charge the batteries with DC, then maybe that's treated differently. But that's such a long shot. If you give details of the new inverter name and model, we may be able to 'guess' a little more.]

I actually did this summer of 24, added DC side batts to my 2011 FiTs system, also with EDF. Beforehand they advised on procedure and a list of actions. I was a bit more prepared as I was also adding ~3kWp of PV to that system, so needed to make sure 100% that I wouldn't 'muck up' my FiTs. So they needed before and after size info to pro-rata payments. During those e-mail exchanges is when they also explained the battery notification process, and the need for a bi-directional meter.


Back to your understanding of TGM readings - yes, I think you have it spot on. Typically inverter and TGM readings will be similar. The inverters are not rated to the same degree as meters, so typically vary a bit.

If, as you explain, you are checking the TGM against inverter, after batteries have been discharged, then again, yes, I think you should be seeing similar numbers. But as others have explained, there are many possibilities for the difference. Could be a faulty meter, but perhaps best test for that would be to compare annual generation and see if it has dropped off (as much as 50%) over the last 14yrs. Note 2024 was pretty poor,

You can also use the PVGIS tool to get a pretty accurate guestimate of annual generation, and compare that to your actual annual generation.

Edit - PVGIS looks a bit intimidating, but it's OK after a quick play. But if you want me to do it, for a rough estimate, then just provide nearest city (or similar as a rough location), system size in kWp, rough roof pitch, and approx orientation. That should be enough for a rough average estimate of annual generation.

Qyburn

C_Wormcake said:

Hi, QrizB
Thanks for the info.
I was assured by the installers that as the generation level was not changing I would not need to inform anyone. Installers were GRCSolar.  
I will follow up with EDF.
Thanks

You ae supposed to notify the FIT provider, certifying whether or not the battery is capable of being charged from the grid. If it is then they'll need a schematic and details of the metering arrangements.

QrizB

C_Wormcake said:

Installers were GRC Solar.

Ah.

https://find-and-update.company-information.service.gov.uk/company/13843999