Devices to meter kWh

[Munroast]

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

What I am wanting to do;

for the last 25 years I have kept a weekly record of my electric (and gas) use. I just like data (sad really but there we go)

We have just had solar fitted and it would appear that there is a lot of wastage in the generation, and battery storage, and it would appear that this is now presented as my own consumption. For example we typically use 90kWh a week, but in a week where we coulld be exporting 200+kWh in a week, my usage will appear something like 140kWh - all free but it is a false reflection on what we are using

In the picture below; 1 is the Grid, 2 is the connection to the Inverter, and 3 is the connection to the consumer unit
My usage data now comes from the Inverter and is clearly including all the losses - would putting some sort of device on 3 give me my true usage which would be comparable to pre solar ?
I see the installers have put some sort of device on the Grid side that communicates with the inverter - could I do something similar on the meter side?

 

[robinbanks]

Google "lantern power monitor" - I was going to build one and monitor every circuit int he house before I was offered the opportunity to use a set of WattWatchers (the rolls Royce of power monitoring, but with a price tag to match) for a year. I also use NDmeter but no idea of the price on those, and another forum I'm on (renewables/passivhaus related) have a few OpenEnergyMonitor fans

There are fairly cheapo devices available it seems, no idea if they're any good but at the price they are I suppose worth a punt; https://www.amazon.co.uk/Monitor-Bi...ectricity/dp/B0DG2WMB4S/ref=asc_df_B0DG2WMB4S

 

[JohnW2]

We have just had solar fitted and it would appear that there is a lot of wastage in the generation, and battery storage, and it would appear that this is now presented as my own consumption. .... My usage data now comes from the Inverter and is clearly including all the losses .... would putting some sort of device on 3 give me my true usage which would be comparable to pre solar ?

I'm not quite sure what you mean by "true usage"., Your meter obviously should give true figures for total import and total export, and those figures are all the supplier has to work with, and hence presumably are what matters in terms of billing and payments?

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

Never having had the need, I don't know any details, but there are a lot of means of measuring kWh out there, and the technology is so relatively simple that I would imagine that most of them are probably pretty accurate. I'm sure others will know what is available, and may have recommendations - but, as above, we (at least I) would first need to have a proper understanding of exactly what it is that you actually want to measure.

 

[ericmark]

I have also considered repairing the old one issued by Scottish Power years ago. Yes, the smart meter measures import and export, often zero, as the house is running off solar and the battery, but my solar software shows what I am using both from the consumer unit and the UPS combined, any CT coil would only show the consumer unit's use, it would not show the UPS use.

 

[Rodders53]

I'd have expected the inverter-battery device to monitor a lot of internals as well as the grid Import (+/- there's no de facto standard afaik) and Export (-/+)...

My EV charger monitors the grid +n kW input via a CT on the grid tail, and charger to car (also +ve) via a internal CT (used to limit EV current if necessary from 32A to lower)...
The grid CT is directional and when it was 'reversed' showed a -ve grid kW number and then the Solar also showed as -ve. I don't have Solar panels.

You may need to ensure that the CTs and measuring devices you choose can tell if current is flowing into and out of the devices they clamp around (as not all will, especially at the cheap end of the market.

It will matter for the inverter-battery (if you charge on off peak electric for example) and the grid connections. Not so much on the CU - until you get an EV fed from it and that EV is capable of V2H...

 

[Munroast]

I'm not quite sure what you mean by "true usage"., Your meter obviously should give true figures for total import and total export, and those figures are all the supplier has to work with, and hence presumably are what matters in terms of billing and payments?

Never having had the need, I don't know any details, but there are a lot of means of measuring kWh out there, and the technology is so relatively simple that I would imagine that most of them are probably pretty accurate. I'm sure others will know what is available, and may have recommendations - but, as above, we (at least I) would first need to have a proper understanding of exactly what it is that you actually want to measure.

I really would not of thought my first post was that difficult to understand - but it has clearly lost you

"True Usage" is the kWh we use to power our house (everything that flows through the consumer unit. In the 25 years up to solar I have just read the meter reading every week.
But since solar panels very little power comes through the supply meter (400Wh last week) and the data I can access from my inverter is considerably higher than my normal use as it accounts for all the waste and inefficiencies.

I am hoping if I attach a meter at position 3 (see image above) then I would get the true figure of the power we are actually using.

You may need to ensure that the CTs and measuring devices you choose can tell if current is flowing into and out of the devices they clamp around (as not all will, especially at the cheap end of the market.

what energy would be flowing back out of the consumer unit ?

 

[Why Not Indeed]

Shelley EM will do it. Pretty cheap. Yes, put a CT clamp on (3) to measure your consumption.
You can probably derive this figure from your inverter as it already knows (1) and (2).

 

[JohnW2]

I really would not of thought my first post was that difficult to understand - but it has clearly lost you

What I seem to have misunderstood is your interest/'motivation'. I had assumed, seemingly wrongly, that your interest was primarily in relation to 'money' (i.e. cost of imports and any payments for exports) - and, as I wrote, that data is inevitably available from your meter.

"True Usage" is the kWh we use to power our house (everything that flows through the consumer unit.

OK. That's what I would have expected, but I got a little confused by the fact that I thought (probably incorrectly) that you were implying that it should be similar to the inverter output.

But since solar panels very little power comes through the supply meter (400Wh last week) and the data I can access from my inverter is considerably higher than my normal use ....

That's where I had some uncertainties, in particular what the data you're getting from your inverter represents. If the data you're being given relates to the total output of the inverter, then that would presumably be equal to your 'true usage' PLUS whatever you had exported. Is that what you've been assuming?

.... as it accounts for all the waste and inefficiencies.

Again, IF the figures you're seeing relate to the output of the inverter, then there will be no significant waste/deficiencies beyond that point - and since you have (and probably could not get) any data about the energy input to the inverter (or the energy output of the solar panels), I'm not sure how you could quantify or monitor those wastes/inefficiencies.

I am hoping if I attach a meter at position 3 (see image above) then I would get the true figure of the power we are actually using.

IF, as seems to be the case, only the energy representing your total usage goes to the CU, then, yes, a measurement at '3' would give your total usage - which, as above, should be equal to the total inverter output (which I suspect is what is being reported to you) MINUS whatever had been exported.

However, as I've implied above, I'm not really sure how that information/data is going to help you very much.

 

[Munroast]

IF, as seems to be the case, only the energy representing your total usage goes to the CU, then, yes, a measurement at '3' would give your total usage - which, as above, should be equal to the total inverter output (which I suspect is what is being reported to you) MINUS whatever had been exported.

However, as I've implied above, I'm not really sure how that information/data is going to help you very much.

my only real sort of data now is from the Growatt dashboard - and this is giving me much higher home use than I expect, 18kWh per day instead of 12kWh a day.
I'm fairly certain that this disparity is the natural losses and inefficiencies. This afternoon when it was sunny and the output from the panels was 7.9kW, I switched the consumer unit off and the dashboard was telling me my load consumption was varying between 250 and 320w (this must be the inverter ?
And then there is stuff like the batteries - this week. 50kwh in, 44.3kWh out - so there is 6kWh gone AWOL
these losses are expected but they should not be included in my personal / load consumption


how will this Data help me? two fold - I have kept weekly records for Gas and electric for past 25 years, it would be a shame to give up that now
and secondly -
I intend to keep a running tally of savings to assess 'payback' in real terms. If I was to believe Growatt, then last week I would have saved
140kWh at 24p = £33.60

however I think my true usage would have been about 90 kWh
90kWh x 4 = £21.60

quite a difference ?

Does Growatt (this being the Solar equipment supplier) purposefully include natural losses so the end user thinks his savings are greater than they really are ?

 

[StephenStephen]

Maybe a spreadsheet to assess the (fluctuating daily) hourly pay rate you receive in savings made per time spent on calculating and recording it would be useful?

More seriously, if you're interested in payback, and have solar and battery, surely you're on T.O.U. tariffs for import and export?

 

[StephenStephen]

Just for clarity - by 'true usage' do you mean:
'the amount of energy that is consumed by appliances within the house, excluding the energy used by the solar and battery appliances'

I guess one could make the argument that the energy used by the solar and battery appliances are actually part of the energy used by appliances in your home...

 

[JohnW2]

my only real sort of data now is from the Growatt dashboard - and this is giving me much higher home use than I expect, 18kWh per day instead of 12kWh a day.

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?

I'm fairly certain that this disparity is the natural losses and inefficiencies.

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 ....

.... I switched the consumer unit off and the dashboard was telling me my load consumption was varying between 250 and 320w (this must be the inverter ?

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'

And then there is stuff like the batteries - this week. 50kwh in, 44.3kWh out - so there is 6kWh gone AWOL .... these losses are expected but they should not be included in my personal / load consumption

As you say, one expects appreciable in/out 'losses' with batteries - but, as you also say, that does not affect your personal consumption. If there are 'losses/inefficiencies' anywhere in the solar/battery system, they are essentially things you will 'never know about', since they will appear downstream simply as solar generation figures which are lower than they would have been without the losses/inefficiencies (but you presumably won't know anything about that).

Talking of the batteries, can we be sure that it is not somehow managing to regard some of the battery charging as being 'your consumption' ?!!

how will this Data help me? two fold - I have kept weekly records for Gas and electric for past 25 years, it would be a shame to give up that now ...

OK, definitely a man after my own heart, so I cannot argue with that one!

....and secondly - I intend to keep a running tally of savings to assess 'payback' in real terms.

OK, that's also very laudable - and something I would certainly want to do if I were in your position (which I never would or will be ).

If I was to believe Growatt, then last week I would have saved ... 140kWh at 24p = £33.60 .... however I think my true usage would have been about 90 kWh 90kWh x 24p = £21.60 .... quite a difference ?

Indeed. As you proposed, just monitor the energy in the tail entering your CU (your "3") and find out what your true consumption ('obvious sense'!) actually is !

Beware that the clip on sensors can only monitor current, but one needs to also know voltage to calculate kWh. Some of the monitors have a connection to the mains so that they constantly monitor voltage in real time, and hence do the calculations accurately - and that's what you really need. Others (probably the majority, certainly of the cheaper ones) do not/cannot measure voltage but have to be programmed with a 'fixed' figure for voltage by the user - that is obviously less accurate and cannot take into account the variations in voltage which happen all the time.

Kind Regards, John

 

[ericmark]

I switched the consumer unit off and the dashboard was telling me my load consumption was varying between 250 and 320w (this must be the inverter ?

If looking at my system, that is about right, as three freezers and the central heating are direct from the inverter, and not fed from the consumer unit. And will continue to work in a power cut.

 

[Munroast]

If looking at my system, that is about right, as three freezers and the central heating are direct from the inverter, and not fed from the consumer unit. And will continue to work in a power cut.

nothing like that on mine - apparently nothing will work if we have a power cut.

Did you have an earthing rod installed when your system was installed ?

 

[ericmark]

Did you have an earthing rod installed when your system was installed ?

Yes, required when the grid fails.