Best way to wire Inverter to Household/Grid for easy monitoring?

[Mozzerr]

Having had our PV installations (mine and dad's) a couple of weeks now, we've had time to get used to living with it etc. and our attention has now naturally turned towards monitoring the system in order to try and make optimal benefit from it.

The installers supplied an OWL basic wireless monitoring device connected via a CT sensor to the live feed coming from the inverter into a spare MCB in the consumer unit. This allows us a convenient, portable indication of how much the panels are generating at any given time - useful given that the inverter itself is housed in the loft.

In order to see our household consumption we purchased separately a second similar device and placed the CT sensor as directed over a live feed coming from the main electricity meter.

After much deliberation and scratching of heads we have come to realise that the indicated consumption on this second device is not ideal due to the inability of these CT sensors to establish the direction of the current flow! Hence it seems we are unable to clearly and conveniently tell when and by how much we are importing or exporting...

So... To my main point.. All of the above has ultimately lead me to the following linked page...

Solar PV Monitoring System | OpenEnergyMonitor

...whereupon there are shown two alternative schematics (about one third of the way down the page) for how a solar PV system - particularly the inverter - may be wired into the household wiring and grid. Our system (like most it seems) appears to be wired as per the type 2 schematic - whereas it would appear to me that for what I would like to achieve, the type 1 layout would seem to be more appropriate. My trouble is, I do not quite follow how the type 1 layout works?? Particularly, what is going on in the "junction block" that still allows the grid, consumer unit and inverter to all be wired together - yet there only be a single direction of current flow in order to make the consumption CT sensor operate as I want for my simple monitoring solution to work?

Obviously I'm no electrician..! Perhaps I'm just being thick, but I don't see it.

Can someone please explain? I'd really appreciate it.

Thanks in advance.

 

[danesol]

Wouldnt you not be better spilting your tails from the electric meter, fitting an Henley block and giving the inverter and associated generation meter its own direct feed. This way a sensor on the tails going to the CU would give true useage and a monitor accessing the figs from the Inverter itself would give the generation figs to save you going in the loft ??

 

[langstroth2]

Wouldn't you not be better spilting your tails from the electric meter, fitting an Henley block and giving the inverter and associated generation meter its own direct feed. This way a sensor on the tails going to the CU would give true useage and a monitor accessing the figs from the Inverter itself would give the generation figs to save you going in the loft ??

I think that is essentially the type 1 diagram mentioned in the link provided by Mozzer? That's how I have mine wired with a junction box (Henley block) two CT sensors and monitors, one on the CU feed and one on the feed from the inverter. What it doesn't give you of course is the amount exported - and i don't think that's possible with a CT sensor as they can't sense current direction.

My trouble is, I do not quite follow how the type 1 layout works??

This is my non-technical understanding: The current from the inverter flows to the junction box. Depending on house demand, it then either:
- If house demand exceeds what the panels are producing, the "solar current" "joins" the current coming from the mains via the electricty import meter and flows into the house via the Consumer Unit (fuse box) to satisfy house demand. Thus less current is required to flow through the electricity meter from the external mains to support house demand.
OR
- If house demand is less than what the panels are producing, some "solar current" flows into the house to satisfy house demand; the rest flows out through the electricity meter and out the house onto the external mains supply. Thus current flows out through the electricity meter from the house to the external mains. The electricity meter probably either runs in reverse rolleyes2, displays RED or a different coloured LED to indicate 'reverse current'. Either way it records no electricity use.

 

[danesol]

Fact:- Only your generation meter will tell you how much you are generating from the inverter ( whether used internally or not ) therefore in theory, the only way you exactly know what you are exporting as "surplus to the house's needs" in any point in time ( real time only ) are by taking the actual sensor reading on the CU tails ( total energy used by house regardless of its origin ) and substracting what you know you have generated as recorded on the GEN Meter at that moment in time. The difference given its a positive no is the theoretic export surplus. You cant use your Electric meter reading as that if OLD may go backwards, plus that only records amount of electric coming into the house to make up the difference for when your PV installation is unable to supply demand.

If you can get a monitoring to system to do this automatically thats great, but worthless info really as at the moment all Energy providers pay you 3p for 50% of the total generated meterage anyway..... !

I record daily;

1. What is generated from the GEN meter

2. The reading on the Electric Meter ( DNO )

3. The reading my Energy Monitor says I used in the house in total regardless of origin ( sensor on the CU tails )

As explained above, with this information you can workout a few things.....................

 

[Mozzerr]

Thanks to all... I get how it works now!

Essentially we are splitting the connection between the Inverter and the DNO Electricity meter - where, currently with my set up, the two are simply connected together via a spare "way" on my Consumer Unit. Splitting out the CU and the DNO Electricity Meter by way of the Henley block allows a single direction of current flow to be moitored whereas with my current set up, it doesn't!

What it doesn't give you of course is the amount exported - and i don't think that's possible with a CT sensor as they can't sense current direction.

Well surely, if the reading on the CT sensor that is indicating panel generation (tapped between the Inverter and the DNO Electricity Meter) is indicating MORE than the CT sensor that is indicating houshold consumption (tapped between the inverter and the Consumer Unit) then you are exporting by the amount of the difference between the two?

Right, where's my neon screwdriver!!...

Thanks again!

 

[danesol]

Thanks to all... I get how it works now!Essentially we are splitting the connection between the Inverter and the DNO Electricity meter - where, currently with my set up, the two are simply connected together via a spare "way" on my Consumer Unit. Splitting out the CU and the DNO Electricity Meter by way of the Henley block allows a single direction of current flow to be moitored whereas with my current set up, it doesn't!Thanks again!

To be precise..... you spilt the tails (+/-) which would normally leave the Electric Meter ( DNO) and go straight to the CU. A Henley block sits in the middle which spilts the tails (+/-) from the DNO Meter into two supplies ( for want of a better expression )

One for the CU and the other ( dedicated ) for the PV Install

 

[Mozzerr]

Gotya! Thanks. For some reason, my brain could only absorb it from the point of view of the PV generation coming in - rather than from the Grid! Then again, I'm dyslexic! haha.

 

[langstroth2]

Well surely, if the reading on the CT sensor that is indicating panel generation (tapped between the Inverter and the DNO Electricity Meter) is indicating MORE than the CT sensor that is indicating houshold consumption (tapped between the inverter and the Consumer Unit) then you are exporting by the amount of the difference between the two?

That's true - but only real time. I really meant you can't record the amount exported that day/week/month unless you have a way of continuously recording the difference between the two.

 

[Mozzerr]

Ah I see your point... Although again only true for the most basic of the CT based monitors like my OWL one that was put in by our PV installers. The second CT monitor I bought was one of these:-

Current Cost - Reducing your energy bills so you can live a greener life!

... Which a) hold 7 years worth of historical data, and b) can be connected to your PC and the data graphed or uploaded to the likes of pvoutput.org - all of which was not fully possible with the way my system has initially been wired, hence my OP question.

By the way, these particular Current Cost meters are available new on EBay for around £10 to £15 as they are the same ones that are (or were) being given away free by Eon to their customers - many of whom it seems are selling them on. I've already bought two of these for the princely sum of £22 in total... Happy days.