Solar Inverter Metering Query

[Swift Solutions Scotland]

I have a query for all the solar specialists on my network. I am currently fitting/having fitted a solar + battery installation on my house. Anyone who knows me knows that if something doesn't make sense I always ask, I've never been one for doing something just because, 'that's what we always do'.... So here we go:

Left Photo: I have a Smart meter which was installed in 2020. It seems to be the latest type and my understanding is that this meter will happily tell Octopus energy what I have consumed and generated for billing/paying me in regards to the solar generation. (My bills are already automatic based on my usage so this must be working fine as of now on the consumption side)

Middle Photo: I have a Huawei DDSU666 being fitted at the main intake to the property while the DB is being swapped. My understanding is that this device will comminicate over RS485 and tell the Huawei SUN2000 inverters whether the property is consuming/generating so the inverter logic can decide whether to charge the Luna batteries etc...

Right Photo: What exactly is the meter on the right for? It essentially duplicates the function of the meter on the left. Is it just a legacy item from years ago that the MCS standard asks for? Can anyone explain to me in technical terms WHY it needs to be fitted?

(Please don't just comment and say it's an MCS requirement, I've had enough questionable advice and input from the solar equipment supplier already on this project! Which is why I've decided to educate myself on exactly what every component in the system does and how it works)

(I posted this in LinkedIn but have not yet had a response so that’s why it’s written like it is. Thanks!)

 

[Murdoch]

The right hand meter should only read the generation flowing from the PV system

 

[binky]

Right Photo: What exactly is the meter on the right for? It essentially duplicates the function of the meter on the left. Is it just a legacy item from years ago that the MCS standard asks for? Can anyone explain to me in technical terms WHY it needs to be fitted?

They really are a legacy of the FiT scheme, but you never know, that may come back - did I just see a flying pig??? . I'm not sure if MCS still insist on fitting them (probably do), but really it no longer serves any function other than it is quite useful to have to compare Inveter figures with the meter. These are always slightly different as it is an OFGEM approved meter so is in fact calibrated, where as the inverter isn't. The only other thing they are any good for is showing a little red LED when the inverter is shut down but AC is still connected - shows any problem probably isn't the AC connection, the LED flashes when generating, and if there's no LED flashing or permanently on, then you have lost the AC connection.

 

[Swift Solutions Scotland]

They really are a legacy of the FiT scheme, but you never know, that may come back - did I just see a flying pig??? . I'm not sure if MCS still insist on fitting them (probably do), but really it no longer serves any function other than it is quite useful to have to compare Inveter figures with the meter. These are always slightly different as it is an OFGEM approved meter so is in fact calibrated, where as the inverter isn't. The only other thing they are any good for is showing a little red LED when the inverter is shut down but AC is still connected - shows any problem probably isn't the AC connection, the LED flashes when generating, and if there's no LED flashing or permanently on, then you have lost the AC connection.

Hi Binky, thanks for the response. Be interesting to see if anyone can confirm whether the MCS scheme auditors would flag it as a non-conformance or whether they would accept its redundant now.

 

[Murdoch]

Why do you not want it ?

Odd to say the least

 

[Kot]

Hi Binky, thanks for the response. Be interesting to see if anyone can confirm whether the MCS scheme auditors would flag it as a non-conformance or whether they would accept its redundant now.

Yes I also had a generation meter fitted, which is totally redundant in my view, but the installer named it on the MCS certificate lol, which actually they stated the wrong mfg and model and s/n. When raising this with the installer they sent someone out to photograph the meter and then a few days later issued me with a second MCS certificate! they changed the details on the certificate. It was a 90 mile round trip for a photograph so the installer obviously thought it was important for MCS. (Or maybe they are so scared of MCS audits and being dropped lol if they ever do any audits !!!!).

The second MCS certificate, there was a Slight improvement, BUT, they rectified only half the details. So I gave up at that point, frustrated with the bureaucracy lol.
In my view, for my installation, the Solaredge metering is far superior as I dont have to stand on a chair to view it or see the flashing light current power generation status. I guess Huewei will have something similar. Dont you just love theses latest monitoring apps!

 

[Swift Solutions Scotland]

Why do you not want it ?

Odd to say the least

Hi Murdoch, I've fitted a new 2 Row DB for the controls and inverters to wire into and having the inverter feeds common up, then have to go out to the meter then back again just seems like a waste of devices, DIN slots and wiring, it requires me to make additional holes in my new DB and as it doesn't seem to do anything useful I really don't see the point. As Kot mentioned the metering I will use day to day will be the Smart meter for billing and prob the Huawei one for day to day generation, state of charge etc etc. I've had a look at the MCS standard and I'll post what I found below to see what everyone else makes of it. Thanks for the feedback everyone.

 

[Swift Solutions Scotland]

So this is the MCS Standard for PV. MCS Standard For PV

(I haven't yet read the whole document, it's on my to do list)

This is the bit I found relates to metering on page 15.

"5.7.1 A means of recording and displaying the total AC generation of the system shall be installed.

5.7.2 If required for billing and / or payment purposes, the means of recording AC generation of the system shall be a meter approved under the European Measuring Instruments Directive (MID) showing the serial number on the front panel where it could be photographed alongside the make, model and meter reading.

Note: Installation of a MID approved meter would also satisfy clause

5.7.3 The means of recording AC generation, be it a dedicated meter or otherwise, should be accessible and readable by the customer without requiring the use of a tool, ladder or torch"

So my interpretation of this is, as long as there is a serialised/calibrated meter (suitable for billing purposes) on the system that the customer can easily get to, then you've met the MCS requirements. So my simplistic view would be that as all I really care about is how much energy flows out the property (which I want paying for) and how much energy flows into the property (which I pay for) my Smart meter on the property intake fulfills this requirment. Technically it is in the meter box so you need a tool to open it but as it has a remote display in the property, I think it's good enough. So my only guess as to why installers think it's mandatory is what Binky said about it being a legacy thing.

Let me know if anyone reads this differently? Thanks

 

[Kot]

So this is the MCS Standard for PV. MCS Standard For PV

(I haven't yet read the whole document, it's on my to do list)

This is the bit I found relates to metering on page 15.

"5.7.1 A means of recording and displaying the total AC generation of the system shall be installed.

Not that I want to defend this silly statement lol. The key word is system, if you have a battery then it clouds things over as you are generating to store and then maybe use it to fill up ev or use home appliances that never go through the export meter.

5.7.2 If required for billing and / or payment purposes, the means of recording AC generation of the system shall be a meter approved under the European Measuring Instruments Directive (MID) showing the serial number on the front panel where it could be photographed alongside the make, model and meter reading.

Note: Installation of a MID approved meter would also satisfy clause

Lol they still got that wrong in my case!

5.7.3 The means of recording AC generation, be it a dedicated meter or otherwise, should be accessible and readable by the customer without requiring the use of a tool, ladder or torch"

Again in my case the meter is in a cupboard only accessible with a ladder and needs a torch. So much for MCS guidelines

So my interpretation of this is, as long as there is a serialised/calibrated meter (suitable for billing purposes) on the system that the customer can easily get to, then you've met the MCS requirements. So my simplistic view would be that as all I really care about is how much energy flows out the property (which I want paying for) and how much energy flows into the property (which I pay for) my Smart meter on the property intake fulfills this requirment. Technically it is in the meter box so you need a tool to open it but as it has a remote display in the property, I think it's good enough. So my only guess as to why installers think it's mandatory is what Binky said about it being a legacy thing.

Let me know if anyone reads this differently? Thanks

see my comment on 5.7.1 just proves MCS bureaucracy is pathetic

 

[Bob Smith]

Hi Binky, thanks for the response. Be interesting to see if anyone can confirm whether the MCS scheme auditors would flag it as a non-conformance or whether they would accept its redundant now.

I had a generation meter installed with my new inverter (I have a 3.68kW since 2016 with Fit and has a generation meter). My installer said that installing a generation meter is still required even though no one will be asking for the reading.
This said, I don't mind. I always like to have a quick look. It feels good lol.

PS: Also this is the only reliable measurement device to know how much your panels have produced. Of course, you have access to an app, However, this is unreliable. Cloud access is not a life warranty, the connection of your dongle to your router may sometimes fail and the app will be missing data.
When you sell your house, if you ever do, no one will be able to argue how much you generated. This is just my view though

 

[roys]

When you sell your house, if you ever do, no one will be able to argue how much you generated.

They will in my case, as my generation meter died after 10 years with the display going blank, apparently it is not an uncommon problem. Got it changed and sent in pics showing new meter with serial number to my FIT provider,

 

[Swift Solutions Scotland]

How do they work with DC coupled battery storage though? I have a Smart Meter linked Octopus Energy so the Import/Export of the whole house is done via a calibrated/serialised Meter anyway and logged on Octopus's billing system.

I'd be interested to get an official answer from MCS. Potentially I might drop them a line and see.

 

[binky]

How do they work with DC coupled battery storage though?

Some early batteries were tapped into the cables for the solar array, so panels charged up directly from the panels, then released the energy through a standard solar inverter. These are DC coupled batteries, and I haven't seen any of those for quite a long time. All batteries are DC charged, and release useable energy through the inverter as AC to your house. So DC coupled tends to be a slightly misleading term. How old is your battery system?

 

[Bob Smith]

Some early batteries were tapped into the cables for the solar array, so panels charged up directly from the panels, then released the energy through a standard solar inverter. These are DC coupled batteries, and I haven't seen any of those for quite a long time. All batteries are DC charged, and release useable energy through the inverter as AC to your house. So DC coupled tends to be a slightly misleading term. How old is your battery system?

Hi Binky,

not sure I can agree with you.
My new system has the batteries DC coupled with the new PV Panels. There is no conversion between what the panels generate and the battery charging. This is the most efficient as you only convert the current when the house need them.
The generation meter I have only measures the production (generation) of the PV.

DC Coupled batteries are still common. Why are you saying DC coupled tends to be a slightly misleading term?
It only refers to how the current is converted before charging the batteries. In a DC Coupled, there is no conversion and there is on in a AC coupled system.

https://www.deegesolar.co.uk/ac_coupling_vs_dc_coupling_solar_battery_storage/
I know you know all of these, not sure what you are trying to say.

 

[binky]

Hi Binky,

not sure I can agree with you.
My new system has the batteries DC coupled with the new PV Panels. There is no conversion between what the panels generate and the battery charging. This is the most efficient as you only convert the current when the house need them.
The generation meter I have only measures the production (generation) of the PV.

DC Coupled batteries are still common. Why are you saying DC coupled tends to be a slightly misleading term?
It only refers to how the current is converted before charging the batteries. In a DC Coupled, there is no conversion and there is on in a AC coupled system.

https://www.deegesolar.co.uk/ac_coupling_vs_dc_coupling_solar_battery_storage/
I know you know all of these, not sure what you are trying to say.

You havn't been around solar as long as I have. Even so called AC batteries still charge batteries on DC converted from AC, all batteries are DC. I will try to find an old DC system to show you what I'm on about, but the fundamental difference was these released DC into a standard solar inverter. There was no/ little control of the energy release. On a two string solar system they were fitted to one string, stored energy during the day, and released it when the sun went down to effectively give a longer spread of energy into the evening. If you were not using any energy, you lost it to the grid. This didn't matter so much as you still got your FiT payments, they just offered an enhanced ability to reduce your energy bills in the evening. In reality, like all the early batteries, they cost more than they could save you.

 

[Bob Smith]

I know, my bio does not say yet retired and loving it

You are right all batteries are DC and you are referring to early stage. One of the reason I did not accept batteries in 2014 and 2016 when I got my first array installed.
The tech has improved a lot and if my calculations are correct. My ROI that includes the cost of the batteries will be between 7 and 10 years.

To me the batteries can provide good ROI if they are sized right (ie the right ratio storage vs charge/discharge capacity and not only how much you need at night) and not only used to store excess energy but if you trade too.

 

[binky]

Can't beat not having to work anymore, although I still do an odd job to keep me busy.

Early batteries only had 3000 charge cycles, it was an easy calculation to work out stored energy, price per unit to buy it, multiplied by charge cycles, and conclude they couldn't pay for themselves. Costs have dropped significantly, charge cycles doubled, and energy jumped in price. I will be looking to get a set myself towards the end of the year when our current energy deal runs out. We fixed for 3 years just before energu shot up.

 

[Bob Smith]

Can't beat not having to work anymore, although I still do an odd job to keep me busy.

Early batteries only had 3000 charge cycles, it was an easy calculation to work out stored energy, price per unit to buy it, multiplied by charge cycles, and conclude they couldn't pay for themselves. Costs have dropped significantly, charge cycles doubled, and energy jumped in price. I will be looking to get a set myself towards the end of the year when our current energy deal runs out. We fixed for 3 years just before energu shot up.

Will you be building your battery as @johnb2713 did? The best way to have a great ROI

 

[binky]

Will you be building your battery as @johnb2713 did? The best way to have a great ROI

I might do, but I still have access to trade prices...

 

[Bob Smith]

I might do, but I still have access to trade prices...

trade prices should still be applicable for the cells and the parts to build battery. Come on, you know you want to