To Fit Export Meter or Not ?

[TedM]

Due to where in the circuits the total generation meter and the export meter need to be fitted they have to be two separate devices.

It's quite possible to have a dual function import/export meter though, in fact I have one.

Also worth mentioning that it seems that some electricity suppliers are a little wary of registering meters that they don't actually own themselves, even though there is no good reason for this.

As to whether it is better to have an export meter or just accept the deemed % figure, then that depends entirely on the pattern of generation and use. And this is likely to vary between weekdays and weekends, holidays etc. It is not a simple figure to predict and will be different (even if only slightly) for each household. But the vast majority of people with PV, who are out at work all day, would probably be better off with a meter.

 

[Worcester]

Andy,

Nope. as far as I can see it won't work.

I don't see how you can measure the Total Generated with your configuration.

In this (standard) instance you efectively have two supplies and two loads. And one of the supplies (DNO) could be a load depending upon the capacity of the secondary supply (PV) and demand of the primary load (consumer)

So you are measuring three things, supply from DNO, supply from PV, export to dno, and calculating or measuring a fourth (consumption by primary load)

Wichever way you configure your meter, as fas as I can see an installation will still need two new meters, your meter will work fine for measuring the export (and supply from DNO) in that configuration it won't measure total generated (supply from PV)

Sketch me out a cricuit diagram and I'll check it out. Bearing in mind also that in some instances the PV output is connected to a spare connection in an existing consumer unit, and in others it's connected in between the main meter and the consumer unit.

 

[Worcester]

@Des Platt

Hi Des, you 'benefit' 3 ways.
1) You get paid to generate wether you use it or not (hence Total Generation Meter)
2) You'll save on your existing bill, by not 'importing' when you are generating (daylight needed)
3) You'll get paid for what you don't use as an 'export'.

Your system has to have been installed by an MCS certified installer for you to be eligible for (1) and (3) above

Export: most FIT suppliers won't bother to install an export meter, so they take a deemed figure of 50% of the amount generated - hence the discussion over wether to fit an export meter or not ..

With regard to theat generated during the day / used at night - the only way that could happen would be if you stored the energy locally with say a set of batteries. Battery storage is not yet an economical proposition when you are connected to the grid. So the short answer is no, what you don't use at the time of generation is 'exported'.

Depending upon who you signed up with for your FITS payments will define how you get paid (cheque or to bank) your FITS payments is a completely seperate arrangement from your electricity bill and they can be two completely seperate companies, your provider if one of the big 5 MUST take you, others can. You can also swap who you get your FITS payment from if you wish.

See this guide from REALAssurance: http://www.realassurance.org.uk/pdf/feed-in-tariff-scheme-guidance-for-consumers.pdf

If you really want to know what you are using and when you you are using it, you need to constantly monitor your usage, import and generation properly so fit a monitoring system with three monitoring points. Current Cost - Reducing your energy bills so you can live a greener life (the data can be uploaded to Google Power meter for analysis Google PowerMeter - Save Energy. Save Money. Make a Difference. )

 

[SibertSolar]

@Worcester

As discussed on the phone (thanks again) I see where the confusion is now. I need to talk to our primary source as I believe that they are confusing where the location of these secondary generation meters is intended to be. The functionality of these import/export meters is somewhat misunderstood it seems and is wholly dependant on where they are installed within the PV/consumer/supply circuits. I'll come back to this thread once I've digged a little deeper and spoken to a few colleagues,

Thanks again,

Andy

 

[Des Platt]

Thanks very much Worcester for taking the time for that thorough reply . I understand that much better now. I think I will do without the import/export for now as may retire next year which will obviously change the usage pattern significantly. I will see how it goes in the meantime. If I can ever reciprocate by providing you with any enlightenment about mortgages I'm on [email protected] or 07970 625024.

 

[SibertSolar]

Hi all,

I'm going to resurrect this thread as I have some new info from Landis & Gyr on how the 5235 import/export meter is designed to work within an on-grid solar PV installation.

Questions first though - when the DNO is notified of a new installation, are they bound by regulations to check the existing primary import meter to see if it can register reverse energy (ie, work as an import/export meter)? If it cannot, are they bound by regulations to fit a new import/export meter regardless of whether the consumer wants to avail of the export tariff? Or do they just offer the 50% (typical) FiT rebate payable against total generated power so as to avoid having to fit new import/export meters?

Who has the right to decide? The consumer or the DNO?

Thanks, Andy

 

[TedM]

The supplier is obligated to ensure that the house does not have a meter that can spin backwards. Anything other than that is optional. If the meter needs to be replaced then the owner may request that an import/export meter is fitted but the supplier does not have to comply with the request.

To understand the roles and responsibilities of metering see -

http://www.ofgem.gov.uk/Sustainabil...rrang/GenerTechs/Documents1/2201-metering.pdf
http://www.elexon.co.uk/ELEXON Documents/section_k_simpleguide.pdf
http://www.elexon.co.uk/ELEXON Documents/section_l_simpleguide.pdf

 

[SibertSolar]

Many thanks Ted, that's as I thought then pretty much.

The reason I asked the question is that it seems to me that most consumers wont know whether they will be better off with measuring total generation and usage, and also availing of the additional export tariff, or just taking the 50% generation tariff as a flat rate from the DNO, regardless of how much of their generated power they actually consume. However, I would imagine that most installers would evaluate the consumer's demand pattern and offer the appropriate advice accordingly.

I've spoke at length with Landis and Gyr and, from their (and Sibert's) point of view, the new 5235 Secondary Import/Export meter that we are promoting is designed to operate in tandem with a Primary Import/Export meter fitted by the DNO. The reason for this is that the dual-display cycles between the below readings/values (corrected from my previous advice above, apologies for the confusion)

t-value = total generated power from Solar PV installation
r-value = the amount of the above t-value actually consumed by the property.

With a Primary Import/Export meter fitted to register export/reverse energy fed back to the grid, the readings from the Secondary generation meter will allow the consumer (and the DNO) to measure all the energy generation and consumption readings necessary to allow the consumer to avail of the full generation tariff AND the additional export tariff.

Secondary Import/Export Meter:
1 - Total Generated Power
2 - Generated power that is consumed by property

Primary Import/Export Meter:
1 - Total imported power from the DNO
2 - Total exported power to the DNO

Hope this helps to finally clarify the potential benefits of these new Secondary generation meters, and also perhaps highlights an area within the sector where a certain degree of consumer "education" is required? If I'm on a learning curve myself then I can bet my bottom dollar that most consumers/end-users are too!

Any advice/feedback/opinions appreciated!

 

[TedM]

I'm afraid I still can't see how a meter that is sited to correctly measure the total generation can also measure how much of that generation is consumed within the property. Do you have any typical installation diagrams to explain it?

 

[SibertSolar]

Hi Ted,

I pleaded the same argument to L&G and they confirmed that the electronics within the 5235 import/export meter are configured to calculate and display the consumption values. How that is actually calculated/measured is beyond me. They are 100% certain on this, and expect that the meter is installed in the normal place as any other secondary generation meter, ie; between the inverter and the consumer unit.

If anyone wants a sample to try out on an installation then by all means contact me and I'll send one out on a sale or return basis.

Thanks, Andy.

 

[TedM]

If this is the right User Manual for this meter -

http://www.sibert.co.uk/uploads/spare_document/filename/8/5235_User_Manual_Version_5_0.pdf

then it is just describing a standard Import/Export meter.

It can be used either as a replacement for the grid meter - where it can measure both import and export to/from the property - or it can be used as a total generation meter with no export being measured.

When current flows through a total generation meter there is simply (without connection to other devices or monitors) no way the meter can know whether the current is going to end up being used in the property or exported to the grid.

Is there a different User Manual for the meter you are describing?

 

[SibertSolar]

Hi Ted,

That is the generic 5235 user manual which I have now removed from the site pending an updated document from L&G. As this new 5235 meter is specially configured for installation as a secondary generation meter within a Solar PV installation, the nature of the dual-display readings is slightly different, as I have outlined today. Once I get an updated document I will upload it to our website accordingly.

Many thanks

Andy

 

[Worcester]

@ Sibert @TedM - if I've got the attached wrong let me know!

Hi Andy, I have a few diagrams, drawings and graphs covering the generation and usage as the real problem is slightly more complicated in that it's not just totals that matter, but also what time of day. - I am working with CurrentCost to come up with a constant PV monitoring system to help educate smarter consumers, output will then be linked to sites such as Google Power Meter.

The point is to get the whole answer you have to measure three places out of four places, 1) Consumption, 2) Generation, 3) Import, 4) Export by measuring any three, then then you can find the fourth. By regulation / default we are measuring Import and Generation, the challenge therefore is either to measure consumption or export, there is no way that I can come up with that could use a dual meter on the Generation leg to give the WHOLE answer, as that particular leg is ONE WAY . The 'import' meter is two way and if replaced, then you can get away with two meters,

So, unless you replace the exisitng import meter, (unless I've got it wrong which I occasionally do), it has to be three meters to give the whole picture, Total Generation Meter, Export Meter and Import meter, or if the PV system is connected between the Consumer unit and the Import meter, then Generation, Import and either Export OR Consumption.

So for what the customer needs I can't see any benefit of it being able to take two readings.

These are just meant to illustrate the problem, highlighting the type of cable was because CurrentCost can only loop round one conductor just like a meter does (any one else got another variation?):
View attachment SolarPV_Layout_000.pdf

 

[SibertSolar]

@Worcester

As I mentioned in my latest update post, the trick to getting the secondary meter (import/export) to function properly is to have the DNO change the primary (utility) meter to an import/export version as part of the MCS/installation registration process. If this is done then the primary meter measures imported and exported energy from/to the DNO and the 5235 import/export meter, installed as a secondary generation meter between the inverter and the consumer unit, measures the total generation and the consumption of that generated power.

I've asked L&G how the import/export secondary generation meter actually "measures" the consumed generated power and will update the thread if I am able to. Other than that, they tell me that it will work in that configuration. All I can suggest is that "someone" installs one and evaluates it perhaps?

Andy

 

[Worcester]

@Sibert

You're right, that's the only way, replace the import meter. However some people want to find out first whether they want to make that call, hence the need for a simple way to collect enough information to be able to make that decision, either compare consumption with import or export with generated.