Consumption correlates with PV Output

[thfctom]

Hi all,

Loving this sunny weather, watching the export tick over nicely.

I've noticed for a while that my consumption correlates almost exactly with PV generation. Every time the PV generation peaks/troughs, the consumption peaks/troughs.

See chart below. Base load is roughly the same through the day until dinner time in the evening or the odd kettle boil.



Is this normal?

Is there a reason for this? Does the inverter use more power when it's dealing with more power through it?

Thanks,

Tom

 

[Badger]

Pv generation,

Here's ours from today

Yellow is pv generation
Green is battery charge
Orange is house load running everything around. The house

 

[David_1224]

Interesting observation.
Not something I'd really paid much attention to as I use the app simply to get a quick overview of what the system is up to.
I actually base expectations and monitor performance on metered readings, (Utility and Export), rather than those reported in the app.
I see you have a Growatt system, as do I, so I can confirm that the parameters you are looking at do exactly the same on my system.
During a day with good PV output the self consumption / load consumption parameters have a profile which tends to track the Solar production curve. Obviously with the odd pop and bang from kettles ,washing machines, etc.

I originally thought the "self consumption" parameter was going to attempt to provided some sort of "efficiency" reading but quickly realised it's simply what the inverter records as "system production" less "export to grid". Hence its very close to the reported load consumption value.
Looking at my records I can see that on good PV days the reported Load Consumption from the app can be as much as 25% higher than what I calculate from metered readings. I also know that on those particular days the property was running on background consumption all day i.e. no additional whatty inputs, so have a very good idea of what it should be and it aligns much better with my calculated figure.

I'm going to make the assumption your inverter is using a CT clamp to record import / export to the grid rather than a meter and suspect this to be the source of the discrepancy. The clamps very unlikely to have a nice linear response and doubt that Growatt would have done much to make allowance for this. So when we get plenty of PV input, and the inverter is well loaded, the value is being overreported.
On a very poor PV day, when the inverter is doing much less work, the app and calculated figures differ by as little as a few %. Well within measurement error.

Don't think there's much for you to worry about .... unless you're wanting to use those numbers for something specific.

 

[thfctom]

Thanks for the input David, good to get reassurance that it's probably just overreporting.

Might do a check vs my actual meter readings and feed back.

Cheers,

Tom

 

[binky]

Interesting observation.
Not something I'd really paid much attention to as I use the app simply to get a quick overview of what the system is up to.
I actually base expectations and monitor performance on metered readings, (Utility and Export), rather than those reported in the app.
I see you have a Growatt system, as do I, so I can confirm that the parameters you are looking at do exactly the same on my system.
During a day with good PV output the self consumption / load consumption parameters have a profile which tends to track the Solar production curve. Obviously with the odd pop and bang from kettles ,washing machines, etc.

I originally thought the "self consumption" parameter was going to attempt to provided some sort of "efficiency" reading but quickly realised it's simply what the inverter records as "system production" less "export to grid"

So is it recording battery charging as self consumption, or just what gets fed into the house from battery and the panels?

 

[David_1224]

The way Growatt report in the app.
"System Production" is what's fed to the property from battery and panels.
They then take the "Exported to grid" value (in our case measured by a CT clamp) from this and report as "Self Consumption".
The "Load Consumption" they report is simply "Self Consumption" plus the "Imported from Grid", which will also be derived from the same CT clamp.

I don't think the term "self consumption" is particularly helpful or appropriate.

Battery charging isn't included in these numbers.
They do provide figures for Solar Production; Battery Charging and Discharging in another part of the app, but I'd guess these should be treated as indicative rather than absolutely accurate.

What I did do on my system however was have a bi-directional export meter fitted which not only records the system output but (mainly in the winter months) will record any battery charge derived from the grid.
That way I can be clear as to exactly how much grid import has gone to battery (zero in summer) and what's gone to load.

 

[Dricah]

Great to hear your exports are doing well! That chart is pretty interesting. I've seen similar patterns with my setup too. It's neat how closely they align. Have you thought about adding a battery to store some of that excess energy for the evening peaks? Might help smooth out the consumption a bit more.

 

[Badger]

What I did do on my system however was have a bi-directional export meter fitted which not only records the system output but (mainly in the winter months) will record any battery charge derived from the grid.
That way I can be clear as to exactly how much grid import has gone to battery (zero in summer) and what's gone to load.

Can I ask which meter do. You have and do. You know. What the wiring connection is how it is wired into the system

 

[thfctom]

Great to hear your exports are doing well! That chart is pretty interesting. I've seen similar patterns with my setup too. It's neat how closely they align. Have you thought about adding a battery to store some of that excess energy for the evening peaks? Might help smooth out the consumption a bit more.

Good to hear it’s not just me!

I have a 6.5kw battery system - you can see it powers the house from 9pm onwards and I export from it at the end of the day, then charge it up overnight (not on chart).

 

[David_1224]

Badger said:
Can I ask which meter do. You have and do. You know. What the wiring connection is how it is wired into the system

The original meter was an Emlite ECA2.z (Unidirectional) and I had the ECA2.nz (Bi-directional) fitted in it's place.
Attached are files that cover the specification and wiring.
Note that the .nz variant is wired opposite to the unidirectional .z version.
Position in system is between the inverter and load.