Devices to meter kWh

[Munroast]

Yes, required when the grid fails.

I asked if ours would work in a power cut - and the answer was no, think it was going to be another £500 (which was presumably more than hammering an earth rod into the ground) so I didn't bother

 

[Munroast]

I think this is coming down to the fact that I have no idea exactly what data this dashboard is giving you, and even you may not be totally clear. Is there a manual for this system somewhere that I could look at, which, for example, might perhaps help me to understand exactly what the "18 kWh per day" it is telling you actually relates to?

Again, we (at least I) do not know what the figures you're seeing represent. If it really were telling you what your "true home usage" was, the figure it gave would obviously be your "true home usage" regardless of any upstream 'losses and inefficiencies'. Hence, if it is giving a figure which is higher than your true home use, then it must relate to something other thjan your true home use - but I (and probably you) don't know what the figure does represent. As you go on to write ....

Who knows? ... but if it is reporting 250-320 W uasage at a time when you know that your true usage (in the obvious sense) was zero, then the figure obviously relates to something other than your 'actual usage' - as you say, maybe the inverter or some other parts of the system which it does not regard as being 'your load consumption'

here is a link to the manual (its the 6000 version we have) happy reading

https://en.growatt.com/upload/file/SPH_3000-6000TL_BL-UP_User_Manual_EN_202403.pdf

I think like a lot of things now, we are presented with misleading half truths that look good at a glance. we are conned all the time with 'Spin'

take a look at my Growatt Dash

the data overview is telling, from the two arrays we have SPPT power as 4877w and 3954w (8.83kW in total)
The SPPT is the DC from the panels before it gets to the inverter

we then have 4kW going to the Baterry and 4.2kW being exported to the grid

Then the very curious figure of 650w consumption
this is curious as I have the consumer unit switch off - we are not using a watt of energy in the true sense
I suspect (without knowing 100%) this 650w is the losses when the power goes through the inverter
and they are attributing that 650w to me as if I am getting 650w of free energy

I would expect the SPPT, the export and the Battery charge are all accurate
but the consumption, well that sort of implies it is what I am using

The dashboard is just a misleading con

 

[Why Not Indeed]

250-300W [EDIT or is 650W?] seems like quite a lot of idle usage to me. Hopefully the manufacturer publishes some figures.

 

[JohnW2]

here is a link to the manual (its the 6000 version we have) happy reading

https://en.growatt.com/upload/file/SPH_3000-6000TL_BL-UP_User_Manual_EN_202403.pdf

Thanks. I'll take a look, and see if it helps, when I have some moments.

I think like a lot of things now, we are presented with misleading half truths that look good at a glance. we are conned all the time with 'Spin'

Maybe - but ....

take a look at my Growatt Dash ..... the data overview is telling, from the two arrays we have SPPT power as 4877w and 3954w (8.83kW in total) ... The SPPT is the DC from the panels before it gets to the inverter. we then have 4kW going to the Baterry and 4.2kW being exported to the grid.

Indeed - although, as below, I'm not sure that 'export' means quite what it appears to (should!) mean.

Then the very curious figure of 650w consumption .... this is curious as I have the consumer unit switch off - we are not using a watt of energy in the true sense .... I suspect (without knowing 100%) this 650w is the losses when the power goes through the inverter
and they are attributing that 650w to me as if I am getting 650w of free energy ... I would expect the SPPT, the export and the Battery charge are all accurate .... but the consumption, well that sort of implies it is what I am using ... The dashboard is just a misleading con

Certainly seemingly misleading, but I don't know whether it is a deliberate 'con'.

The figures, per se, seem to make sense but I'm very suspicious about what they are calling 'export' and 'consumption'. You have a total of 8.83 kW of solar generation, 3.99 kW of which is charging batteries and 4.19 kW is described as 'export', a total of inverter output usage of 8.18 kW, which is 0.65 kW less than the total (pre-inverter) solar generation - that difference being called 'consumption' on your dashboard.

For an inverter to have an input of 8.83 kW and an output of 8.18 kW indicates an efficiency of 92.6%, which would seem very reasonable/expected (probably higher than I would have guessed) - so I think that the displayed figure of 0.65 kW (the difference between inverter input and output) probably represents the (expected) 'conversion losses' (manifested as heat) in the inverter - even though it is described on the dashboard as 'consumption'.

Looking at you photo, it would appear that the inverter is connected directly to both the grid and the CU (in parallel). If that is the case, then all the inverter could know would be the total of export and 'true usage' (via the CU) combined - i.e. it could not know how much of its output was being exported and how much is actually being 'consumed' (locally, by you). I would therefore think that the figure reported on the dashboard as "export" therefore is probably 'export PLUS true consumption' - and, indeed (unless I'm missing something), there would appear to be no way that the dashboard could know your "true usage/consumption" (via CU).

If my theory is correct, then if the amount of power charging batteries does not change appreciably, I would expect that, providing you were generating at least as much as you 'needed' (for "true use"), and provided the amount of solar generation did not change, when you switched on loads in you house, the dashboards figures for "export" (I believe 'export+true use') and 'consumption (I believe 'inverter losses') would not change appreciably - since the inverter losses would remain the same for an unchanged amount of solar generation, whilst there would simply be a shift of the proportions of power being exported and actually used (leaving total export+true usage {which I think is probably being displayed as 'export'} unchanged)

Does all that make at least some sense?

 

[Why Not Indeed]

If that is the case, then all the inverter could know would be the total of export and 'true usage' (via the CU) combined - i.e. it could not know how much of its output was being exported and how much is actually being 'consumed'

I would be astounded if the inverter's CT clamp was not "directional". The inverter knows how much it's outputting, it knows what is passing through the CT clamp, the difference has to be consumption.

 

[JohnW2]

I would be astounded if the inverter's CT clamp was not "directional". The inverter knows how much it's outputting, it knows what is passing through the CT clamp, the difference has to be consumption.

One might have thought so, but can you think of any way of explaining what the dashboard is displaying other than what I was theorising?

In any event, if it were working as you suggest, with the displayed "consumption" being the difference between inverter output and (true) export, then when true consumption was zero (as it was in the example we've been shown), then the displayed consumption would also be zero (not 0.65 kW).

The OP can presumably test this very easily by turning on some significant loads. Provided that the battery charging remains much the same, as I explained, if my theory were correct then the displayed figures for "export" and "consumption" would presumably remain much the same - since the total of export+use would be unchanged. However, if it were as you suggest then displayed "export" would decrease and displayed "consumption" would increase.

 

[JohnW2]

here is a link to the manual (its the 6000 version we have) happy reading

https://en.growatt.com/upload/file/SPH_3000-6000TL_BL-UP_User_Manual_EN_202403.pdf

It may be called a "User Manual", but it all seems to be about installation and commissioning, with no reference I can find to the 'dashboard' display you have shown us, let alone any explanation as to what the figures displayed on that dashboard represent. In fact, the word "dashboard" does not appear anywhere within its 75 pages, and the only illustrations of the 'display' show something entirely different from what you showed us.

Am I missing something and/or is there any more useful documentation available?

 

[Harry Bloomfield]

What is available to meter kWh, how accurate are they, and for what sort of cost

Your suppliers meter, is the only really accurate way to determine consumption, that's what you will be charged for. Nothing you can buy, will agree precisely with that meter, and clip around the cable, current transformers (CT's), cannot differentiate, between which way the current is flowing, in an AC circuit. However....

For upto 60v/30amp DC, this cheap, and very versatile device claims to be able to measure both the direction of DC current flow, and log the amp hours, so it gives you a state of charge of batteries. https://www.diynot.com/diy/threads/interesting-charge-discharge-gadget.645375/

 

[JohnW2]

Your suppliers meter, is the only really accurate way to determine consumption, that's what you will be charged for

Indeed - but that doesn't alter the fact that some is wrong (or 'misunderstood') when the OPs gadetry is saying that he has 0.65 kW of consumption when he knows that his consumption is zero.! I've offered one theory (relating to possible confusing/misleading data being displayed/described).

.... clip around the cable, current transformers (CT's), cannot differentiate, between which way the current is flowing, in an AC circuit.

That's what I thought (and hence would be consistent with my theory), but others seem to have suggested otherwise!

 

[Harry Bloomfield]

Looking at you photo, it would appear that the inverter is connected directly to both the grid and the CU (in parallel). If that is the case, then all the inverter could know would be the total of export and 'true usage' (via the CU) combined - i.e. it could not know how much of its output was being exported and how much is actually being 'consumed' (locally, by you). I would therefore think that the figure reported on the dashboard as "export" therefore is probably 'export PLUS true consumption' - and, indeed (unless I'm missing something), there would appear to be no way that the dashboard could know your "true usage/consumption" (via CU).

Separate cables, from inverter, to CU, and inverter, to meter - would at least allow for monitoring those separately.

 

[ericmark]

Separate cables, from inverter, to CU, and inverter, to meter - would at least allow for monitor those separately.

Not sure why I would want to?

the graph so the 5 main things, and the other options on the Device Monitor page shows most of what is going on.

Since it uses a server in China, there is some lag, but a quick check with my clamp-on meter,

shows not far off anyway. Once one has compared the smart meter and solar software a few times, one soon knows how accurate it is.

I find the smart meter shows I have used slightly less as what the solar software says. And yes, the smart meter is around one day behind on the phone app.

I can see the point in taking a record at 4pm and 7pm to see if worth going onto flux tariff, but only need a few good and bad days, one will soon see what.

 

[Harry Bloomfield]

Once one has compared the smart meter and solar software a few times, one soon knows how accurate it is.

On a purely resistive load. Measuring inductive loads is what smart meters are supposed to do well, so that will cause some difference.

 

[Harry Bloomfield]

That's what I thought (and hence would be consistent with my theory), but others seem to have suggested otherwise!

Common sense, and knowing how AC works, would suggest otherwise.

 

[Why Not Indeed]

Common sense, and knowing how AC works, would suggest otherwise.

Reality is otherwise. I wouldn't have suggested Shelly EM if it couldn't distinguish which direction.
I don't think ultimate accuracy is the goal here, simply sense-checking what the inverter is saying.

 

[JohnW2]

Separate cables, from inverter, to CU, and inverter, to meter - would at least allow for monitoring those separately.

That's obviously not what the OP currently has, but I'm not sure it would, in itself (i.e. without other additional monitoring) necessarily tell him his actual consumption, since it would 'miss' any consumption coming from the grid, wouldn't it? His proposal is to monitor input to CU (whether from inverter or grid) to get an indication of his true consumption, and that seems fine.

However, as before, when the OP produced that data to show us, we know that his true consumption (whether from inverter or grid) was zero, so the 0.65 kW 'consumption' indicated by his gadgetry clearly can't mean what one would expect it to mean!