Customer convinced that generation meter is not calibrated

[liquidity]

What is the inverter saying has been produced?

 

[Gavin A]

Hi,
I have a customer that is convinced that his generation meter is not calibrated and possibly not Ofgem approved. The type of meter we most often install for domestics is a L&G E110 5235 (A in this case). I quit happy the meter is approved and calibrated. For the customers sake we replaced the meter and notified of a meter change with the FiT provider but now the customer says this new one is even less accurate.

To cut a long story short they are using a clip on meter to measure against the generation meter. We provided an OWL device that they are using to compare and also they have tried a standard monitor from British Gas and the likes. They customer reports that both the clip on meters show the same but this does not correlate with the generation meter.

I know the clip on meters are not as accurate as the generation meter and have sent the customer all the supporting information from Landis of the various test approvals and Ofgem approval for the generation meter.

Do any instances exist when the clip on meters are particularly out, maybe with a high proportion of non-resistive loads etc..? Just remembed they customer is on storage heaters if that helps.

One device is accurate and calibrated, the other provides a rough approximation based on a guess at what the grid voltage reading might be.

I'm not really understanding why you're having trouble explaining this one tbh, but try this from Owl themselves

Solar PV installations operate outside the bounds of the electricity monitor parameters for most of the day. At very low power levels (below 500W) the monitor accuracy will be significantly impaired.

Accuracy​

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<1A​

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1A to 3A​

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3A to 71A​

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>71A​

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Current RMS​

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Not Specified​

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Better than 10%​

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Better than 5%​

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and 2 different devices operating on the exact same principles will likely give roughly the same readings, but both readings will still be wrong for the exact same reasons as each other - ie if the voltage is 250V and the meter is assuming 240V etc. and bear in mind that when the inverter is outputing at full power then this will also be pushing the voltage up and increasing the error in the devices calculations.

 

[FB.]

As an earlier poster said: does the inverter agree with the generation meter? Mine are over 99% in agreement; I have a L&G E110 and an Aurora. My incoming electricity meter belonging to the utility company is the same L&G E110. I recently mentioned that I soon planned to stop contributing to PVOutput.org because the data being uploaded by most people's devices was often unbelievable compared to the few people who take readings from their generation meter. The Sheffield Solar Farm insist on readings only from the generation meter.

 

[ktech]

I think once you get into looking at invertors and generation meter readings it becomes another can of worms, i.e. is the inverter reading relating to the DC or AC side, voltdrop issues as well as reactive loads etc..

 

[JD6400]

I think once you get into looking at inverters and generation meter readings it becomes another can of worms, i.e. is the inverter reading relating to the DC or AC side, voltdrop issues as well as reactive loads etc..

Please don't take offence , but how can you fit the gear with out knowing how to use it / set it up .
What inverter is it ?
My personal system is only about 3 units out between the both of them after over a year .

 

[ktech]

Please don't take offence , but how can you fit the gear with out knowing how to use it / set it up .
What inverter is it ?

Eh? Sorry you have completely lost me...

 

[JD6400]

I think once you get into looking at inverters and generation meter readings it becomes another can of worms, i.e. is the inverter reading relating to the DC or AC side, voltdrop issues as well as reactive loads etc..

I am probably wrong , but this post sort of seems to suggest that you have a problem in reading the information from the inverter ?
As i have already said , i am not sure about other inverters but on fronius ones it gives a very easy to understand read out .
Again sorry if i have it wrong , it was not meant to offend .

 

[ktech]

Hi, sorry but you are indeed wrong, no not a problem reading off the inverter. As per original and previous posts issue is with the difference between generation meter and clip on meter monitoring devices, invertor readings never mentioned or implied.

 

[JD6400]

Fair enough , i have had a few tonight .
But please do bear in mind that if the output from inverter matches the generation meter readings , that alone should pacify the customer .

 

[SolarCity]

Although bear in mind that inverter displays can be out too. The only reliable measure of how a system is doing is by looking at the generation meter.

 

[Worcester]

We have 5 different monitoring devices on our various PV generators here.
The Inverters (x3), meters (3 x generation, 2 x import, 1 x export) , immersun and calibrated Solar PV Monitoring System | OpenEnergyMonitor (6 x CT montiors) all tally within about 1%
The two energy monitors, Scottish Power and current Cost have an error factor of between 25% and 50% based on ACTUAL production / consumption.

Speak to them (SP and CC) and they will tell you that they aren't accurate and onlu designed to give the user a guide / base line / indication. The CC version with the pulse meter attachemnt is more accurate.

I VERY much doubt it is the meters at all

 

[FB.]

Although bear in mind that inverter displays can be out too. The only reliable measure of how a system is doing is by looking at the generation meter.

My inverter reads about 0.5% higher than the generation meter. This small difference is probably a result of losses in the few metres of cable from the inverter to the generation meter.

 

[Gavin A]

My inverter reads about 0.5% higher than the generation meter. This small difference is probably a result of losses in the few metres of cable from the inverter to the generation meter.

there's a danger in applying your experience from one system across all inverters.

We were caught out with this assumption a while back, and it turns out that SMA inverters at least don't actually meter the outgoing AC electricity as such, they calculate what it ought to be in watts from the Ampage, and at least on their older models this conversion can be very rough and ready and not actually based on the actual measured grid voltage for some reason - I think it may even be that it's based on measurements of the DC side that are then estimated for the AC side based on some sort of efficiency factor, but I'm not 100% sure. Either way, apparently the SB series output data can be up to 20% out from the actual meter readings, though later models tend to be quite a bit more accurate.

The meter is calibrated, the inverter isn't, and neither are the vast majority of clamp meters, though there are some now that do actually also read the grid voltage and use that to calculate the actual wattage to within around 1% accuracy - Owl ain't one of them though.