AC Cable length question

[Radian]

I only wish I was capable of doing the roof work to self-install as every other aspect is easily within my capabilities. The only contractors I can find that are geared-up for this kind of job are the usual MCS accredited types. Builders are just too busy to want this kind of work it seems and I'm not sure I'd trust any around here anyway.

 

6 minutes ago, ProDave said:

There was an odd comment when getting the home report done for our last house.  The assessor made some comment that he could only take the solar PV into account when calculating the EPC if he could see the generation meter next to the main meter.

 

Now that's interesting, there must have been something that prompted this although it'd be a pretty bizarre stipulation given the highly variable arrangements of arrays and their inverters.

[Radian]

Maybe it's a confusion between generation and export metering. The old Feed-in Tariff scheme had this to say:

 

Quote

Metering scenarios

3.45 FIT generation payments are made based on the total generation produced by an installation. A generation meter is normally located close to the point of generation.

 

3.46 FIT export payments are made based on electricity exported onto the distribution or transmission network. An export meter is always located at the point where the installation connects into the distribution or transmission network.

 

3.47 A generation meter (located as set out in paragraph 3.45) cannot be used to claim FIT export payments. This is because an “export meter” is defined in the FIT legislation as a meter which measures the quantity of export, and export is defined as the flow of electricity from an eligible installation onto a distribution or transmission network. If the generation meter is located at the point of generation and not at the point of connection between the installation and the distribution or transmission network, it cannot be used to claim FIT export payments.

 

I guess this must still apply to SEG. I can understand then how this might affect things but having a smart meter should get around this shouldn't it?

[Radian]

...Either way, the only logical place for an export meter is inline with the grid supply like this:

 

 

So there's nothing I can conceive of that would make it necessary to place a battery inverter in the house rather than have it located on a sub-main in the garage. I'm still waiting for an answer to the question I posed to the company.

[Dillsue]

3 hours ago, Radian said:

...Either way, the only logical place for an export meter is inline with the grid supply like this:

The export meter is the house meter that belongs to the DNO. If its smart it measures electric coming into the house(import) that you pay for and measures electric leaving the house(export) that you could get paid for under SEG. This meter is nothing to do with your PV or MCS installer.

[Radian]

44 minutes ago, Dillsue said:

The export meter is the house meter that belongs to the DNO. If its smart it measures electric coming into the house(import) that you pay for and measures electric leaving the house(export) that you could get paid for under SEG. This meter is nothing to do with your PV or MCS installer.

 

Yes, I called up the relevant menu entry on my meter just to make sure it was capable. I don't know if you've read through all the posts in this thread, but I'm trying to work out why an installer is telling me that either they can't put a battery in my detached garage with PV and inverter or they're telling me I must have a battery in the house (whether or not I want one) in order to have a PV on the garage roof. Neither scenarios make any sense to me so I've been running through all the possible reasons in the absence of a reply from the installer.

 

I've been trying to communicate with them and several installers and am getting no replies from anyone. I think the current energy crisis has got everyone calling up Solar installers. I wish I'd made a move on this when I started looking last year when I started this thread.

[Dillsue]

27 minutes ago, Radian said:

 

I've been trying to communicate with them and several installers and am getting no replies from anyone. I think the current energy crisis has got everyone calling up Solar installers. I wish I'd made a move on this when I started looking last year when I started this thread.

Spoke to our DNO today about adding to our PV and he said theyve seen a big increase in PV related enquiries.

 

In your position Id work out what youre likely to export and see if its worth doing an MCS install.... with 2.4kwp I suspect not.

 

If you bin the MCS installer you can do the install yourself and use any part P spark to connect up the AC for you all totally legit. Assuming its a single story garage the roof work is low risk and fairly straight forward. Buy a second hand alloy tower scaffold and sell it when your done. With your own scaffold theres no rush to do the install and get rented scaffold off hire

[Radian]

OK, finally got the answer as to why we would need to install an AC coupled battery/inverter in the house rather than what we wanted - a DC coupled battery/hybrid inverter system in the garage.

 

I've been told it's because the DC system needs a wired connection to a CT on the meter tails. I asked if this was something that could be provisioned wirelessly and the answer was no, because the DNO's insist on wired connection. There you have it.

 

Naively I though the hybrid inverter would figure out when to charge/discharge the battery based on simple priorities: If battery charging is treated as a priority then all PV goes into the battery until full, then the PV is converted to AC until the sun stops hitting it. The battery would then discharge until exhausted. This, on reflection would defeat the goal of storage for self consumption unless it was pre-set to only convert a fixed amount of power to cover a known base load.

 

But I'm being told the inverter makes a judgment on whether to charge or discharge the battery depending on whether you're importing or exporting. This way the battery is only bought into play to store and recover any excess generation.

Edited March 8, 2022 by Radian

[Ajn]

10 minutes ago, Radian said:

CT on the meter tails

just extend the CT cable with a screened cable but only earth the screen at one end.

[Dillsue]

26 minutes ago, Radian said:

 

I've been told it's because the DC system needs a wired connection to a CT on the meter tails. I asked if this was something that could be provisioned wirelessly and the answer was no, because the DNO's insist on wired connection. There you have it.

That doesnt sound right to me. AFAIK if the PV and battery sit on the DC side of the inverter and you use a G98 compliant inverter then the DNO isnt interested in how anything else works ie how your CT connects to the inverter/battery charger.

 

The DNO may insist on a wired CT(or anything else) if its being used for G100 export limitation but with a DC coupled G98 inverter an export limitation system shouldnt be needed

[Radian]

2 hours ago, Ajn said:

just extend the CT cable with a screened cable but only earth the screen at one end.

 

Still 25m away with a freshly paved patio to cross. If it wasn't for the bureaucracy I'd A/D convert locally, transmit the measurement over MQTT and reproduce in analogue form at the invertor. I suggested this to the installer who wasn't having any of it on account of this not being Type Approved.

 

2 hours ago, Dillsue said:

That doesnt sound right to me. AFAIK if the PV and battery sit on the DC side of the inverter and you use a G98 compliant inverter then the DNO isnt interested in how anything else works ie how your CT connects to the inverter/battery charger.

 

The DNO may insist on a wired CT(or anything else) if its being used for G100 export limitation but with a DC coupled G98 inverter an export limitation system shouldnt be needed

 

Type approval seems to be the catch even with G98 export: Requirements for the connection of Fully Type Tested Micro-generators (up to and including 16 A per phase) in parallel with public Low Voltage Distribution Networks on or after 27 April 2019 includes the requirment for CT's to meet BS EN 61869 (Instrument Transformers: Additional requirements for current transformers)

 

I'm stuffed.

 

[Ajn]

51 minutes ago, Radian said:

I'd A/D convert locally, transmit the measurement over MQTT and reproduce in analogue form at the invertor

While the concept sounds ok I assume the code you write will include all the "what if" failure conditions that you may know about and the ones you don't. Via cable the inverter gets a continuous signal. MQTT will not give you that even at very high sample rates. I run MQTT on a Pi3 and while ok there has been the odd delay or sticking over the last three years and even needing two reboots even though it's on a UPS. For some "on and off" switching activities I have included tripple switching just to make sure in cases where there is not instant feedback. I also ping the various modules to see if they are alive and have a fallback or restart process if not. ...not that you can do it anyway...

Edited March 8, 2022 by Ajn
addition

[Dillsue]

2 hours ago, Radian said:

Type approval seems to be the catch even with G98 export: Requirements for the connection of Fully Type Tested Micro-generators (up to and including 16 A per phase) in parallel with public Low Voltage Distribution Networks on or after 27 April 2019 includes the requirment for CT's to meet BS EN 61869 (Instrument Transformers: Additional requirements for current transformers)

 

In the section referencing CTs, the doc says

"Typically, all interface functions are contained within an Inverter and in such cases it is only 
necessary to have the Inverter Fully Type Tested".

 

I read that as if youre using a G98 inverter any CT or CT function providing interface protection is integral to the inverter. There may be a need for a CT to manage battery charging but thats on the DC side and not part of the export limitation that the DNO is interested in.

 

Id speak to the inverter manufacturer and clarify things with them.

[Radian]

4 hours ago, Ajn said:

While the concept sounds ok I assume the code you write will include all the "what if" failure conditions that you may know about and the ones you don't. Via cable the inverter gets a continuous signal. MQTT will not give you that even at very high sample rates. I run MQTT on a Pi3 and while ok there has been the odd delay or sticking over the last three years and even needing two reboots even though it's on a UPS. For some "on and off" switching activities I have included tripple switching just to make sure in cases where there is not instant feedback. I also ping the various modules to see if they are alive and have a fallback or restart process if not. ...not that you can do it anyway...

 

Sure. I'm very familiar with "the best laid plans of mice and men often going awry" as I have extensive experience in military and industrial engineering design. The knack is, as you mention, to have multiple fall-backs but even more relevant is understanding the risks due to unexpected failures. Frankly in the case of this CT bridge, a complete cock-up in relaying the true state of export/import is only going to result in undesired loss of stored energy within the limits of the approved equipment. That'd be my loss. But I don't think I'm going to get the chance anyway.

 

But you seem to have problems with your Pi that I don't get. I have yet to see a lock-up in the server hosting Mosquitto and that's been running for about as long as yours, along with node-red and a few custom services. Do you connect to your LAN with an ethernet cable?

 

2 hours ago, Dillsue said:

In the section referencing CTs, the doc says

"Typically, all interface functions are contained within an Inverter and in such cases it is only 
necessary to have the Inverter Fully Type Tested".

 

I read that as if youre using a G98 inverter any CT or CT function providing interface protection is integral to the inverter. There may be a need for a CT to manage battery charging but thats on the DC side and not part of the export limitation that the DNO is interested in.

 

Id speak to the inverter manufacturer and clarify things with them.

 

I had a good chat with the installer about this and I've concluded that there's no point pressing them over the issue. It's been made clear that it's 'take it or leave it' situation. The market out there has utterly transformed since the recent geopolitical unpleasantness. I feel the need to get the basics sorted as a matter of urgency. I've lost a week on this already and I'm just getting further behind in the queue.

[Ajn]

12 hours ago, Radian said:

Do you connect to your LAN with an ethernet cable?

we seem to be on the same hymn sheet. Yes its wired. It was running on a zero w but node red started to run slow. Moved it to a spare 3b+ that I was trying to run flexray on (now on hold) All that is running on it is MQTT, node red and SQL lite. I may try a new SD card.

 

The D1 mini and espeasy is my favorite toy at the moment.

 

P.S. Don't know anything about Rapier 1 do you? A friend has one that needs a little work, I suggested we may need it.

Edited March 9, 2022 by Ajn

[Dillsue]

14 hours ago, Radian said:

It's been made clear that it's 'take it or leave it' situation.

Any supplier that makes that sort of ultimatum to a customer whos not getting what they want should get the leave it option by default. Find yourself a roofer, show him the Renusol install video on Youtube, and let him fit  panels and you do the wiring.

[Radian]

2 hours ago, Ajn said:

we seem to be on the same hymn sheet. Yes its wired. It was running on a zero w but node red started to run slow. Moved it to a spare 3b+ that I was trying to run flexray on (now on hold) All that is running on it is MQTT, node red and SQL lite. I may try a new SD card.

 

The D1 mini and espeasy is my favorite toy at the moment.

 

P.S. Don't know anything about Rapier 1 do you? A friend has one that needs a little work, I suggested we may need it.

 

There's a long list of things you can do to bulletproof a Pi. Eliminating reliance on the SD card is top of the list.

 

8 minutes ago, Dillsue said:

Any supplier that makes that sort of ultimatum to a customer whos not getting what they want should get the leave it option by default. Find yourself a roofer, show him the Renusol install video on Youtube, and let him fit  panels and you do the wiring.

 

I also thought I might explore that route so fired of a few emails middle of last week. Not one has replied. I'm still waiting on @joe90 for his proposed thread on DIY PV 😉

[Nickfromwales]

On 03/03/2022 at 17:02, Radian said:

The saving in VAT (5% vs 20%) makes it somewhat attractive to have it done during the PV installation

How are you 5% VAT? Is this part of a large refurbishment?

[joe90]

9 minutes ago, Radian said:

I'm still waiting on @joe90 for his proposed thread on DIY PV 😉

Ha, don’t hold your breath, I have other matters at hand before I can contemplate that one (unfortunately). Luckily my incoming meter is on my workshop where I propose to mount the panels so connecting to the incoming is a 

Piece of cake and no distance 👍

[Radian]

1 minute ago, Nickfromwales said:

How are you 5% VAT? Is this part of a large refurbishment?

UK Gov. Tax on shopping and services

 

VAT on energy-saving products. If you’re eligible, you’ll pay a reduced rate of VAT (5%) when certain energy-saving products are installed in your home.

 

[Radian]

4 minutes ago, joe90 said:

Ha, don’t hold your breath, I have other matters at hand before I can contemplate that one (unfortunately). Luckily my incoming meter is on my workshop where I propose to mount the panels so connecting to the incoming is a 

Piece of cake and no distance 👍

Oh, no problem. in that case I may start it later.

[Nickfromwales]

38 minutes ago, Radian said:

UK Gov. Tax on shopping and services

 

VAT on energy-saving products. If you’re eligible, you’ll pay a reduced rate of VAT (5%) when certain energy-saving products are installed in your home.

 

Read the small print  Over 60's are 5%, and under 60's need to have left 60% of the installation cost ( in materials ) behind to attract 5%. That's assets only, and doesn't include labour / scaffolding etc.

Best to check your individual eligibility first.

[SteamyTea]

14 minutes ago, Nickfromwales said:

 Over 60's are 5%

Does that mean the wealthiest group in the country pay less tax?

[Radian]

4 hours ago, Nickfromwales said:

Read the small print  Over 60's are 5%...

 

Yes, and it's as clear as mud. Still, this is one of those times when being over 60 actually pays off 😉

 

4 hours ago, SteamyTea said:

Does that mean the wealthiest group in the country pay less tax?

 

Wealth as in assets or cash?

[SteamyTea]

4 minutes ago, Radian said:

4 hours ago, SteamyTea said:

Does that mean the wealthiest group in the country pay less tax?

 

Wealth as in assets or cash?

Wealth is assets and cash.

Not the same as richest, which as far as I know, does not have a real, economic definition.

And then there is income.

I am not complaining, just the way things have panned out.

 

Edited March 9, 2022 by SteamyTea

[Radian]

Wealth is made by moving assets from lower to higher value uses The longer people have been doing this then perhaps the more they might deserve state benefits. Dunno. But yes, if there are benefits that people are entitled to then I'm all for them being claimed.