Why does my consumption seem to follow the path of generation?


#1

Any idea why my consumption graph seems to follow the curve of my generation graph, especially on cloudy days? I have the three pushes from Solarweb to PVOutput set up as per BB’s guide.

Cloudy day

Sunny day


#2

Hi cammo i sent you a pm ok jim


#3

Thanks Jim, got your message however should you have just posted here instead? The forums are good to look back through to learn - private messages aren’t helpful to anyone else but the original poster.

I still don’t understand how the peaks and troughs in my generation match up with the peaks and troughs in my consumption? If it’s sunny out then my generation drops but nothing changes with my consumption.


#4

well i did not post here as the info i shared could be used to tell when you are out,

so did you look at the Blue Net generation graph and see what i mean about the air con and the pool pump??. well with your base load when you have clouds your import go,s up to keep up with the load


#5

Ah ok Jim, thanks for that info, totally understand. Didn’t even consider that was a possibility.


#6

The problem of consumption following solar when you have current clamps [not sure of your setup] is when the solar is feeding back through the same consumption clamps. In a case such as that site the consumption clamps correctly or feed the red solar live back through the same consumption clamp to negate the solar in the consumption clamp. Red solar wire needs to be in opposite flow direction. Current clamps are dumb but basic magnetic fields are not.


#7

Looks like your power monitoring setup is miswired. Do you have a drawing or photos of how it’s set up?


#8

This is very typical and is more a factor of the generation variability than anything else. Generation is an absolute value and so is Energy Used. Power used needs to be calculated and will vary a great deal based on the instantaneous Power Generated value. If you have big swings in generation, you are going to see swings in Power Used to make the math work correctly. Notice that the irregular generation periods are similar to yours and the smoother period is more consistent.


#9

That sounds… odd. I measure power generated and used independently, and the two don’t influence each other at all.

Can you expand on your claim?


#10

It is partially dependent on the secondary device you are using and exactly what it measures. In my case, it is a Rainforest Eagle. My primary device gives me Power Generated, the Eagle provides Energy Used (by reading the SCE meter). No device provides Power Used so it must be calculated. I suspect the OP is using a similar device that reads the meter which accounts for the dramatic swings when Power Generated varies.


#11

Hi all,

Thanks for your input. I’ve got a Fronius Primo 5.0 inverter and a Fronius Smart Meter for those that were wondering about my setup.

Cam


#12

MrFusion, can you explain how and where you are measuring Power Used? Power Generated can be measured at the output point of the Solar Array. Where are you getting a value for instantaneous Power Used that is not calculated based on generation and energy consumption? Thanks!


#13

Quite simply. I have one power meter reading the PV output (which I also verify against what the inverter thinks its producing), and one power reading house consumption.


#14

well problem solved, inverters do,not export straight to the grid and then re import to the house.
inverters are wired to supply the house first and then export any excess to the grid, so if you drop the reporting of the power meter on the inverter and use the inverter output instead and change your setup in pvorg to reflect this you should get true readings.
yes thats better , can your house power meter read in both directions ?? because as its wired at the moment its is only reading total power used by the house from the grid and the inverter as well…PV output should go to the house first and then flow out to the grid through the house meter ,Not into the house through it because as is pv org is seeing it as load not output and load, i think pv org is set up to read inverter output and total house input and export and do the calcs itself,possible the settings in pv org can be changed to fix this without having to rewire correctly, i hope,
sorry for that i thought YOU had a problem so i replyed if i had known you were just talking i would not have bothered, yes this is my fault for not reading back to the start of the post and addressing my comments to Cammo


#15

Sorry - maybe this diagram is more clear…


#16

I don’t have any issues. My system is correctly wired and working properly.

All my power meters are bidirectional (though only really necessary on the nett meter), are accurately reading all power generated and consumed, and my nett power meter agrees precisely with the utility’s power meter.

The above diagram is purely to explain how one can properly and directly measure all aspects of generation and consumption (even though I have a redundant meter, as I can use any two to derive the third.).


#17

I hope the above diagram helps.

The meters provide both energy and (instantaneous) power readings.

Keep in mind - “energy” (kWh - a reading over time) is merely the integral of “power” (kw - in instantaneous reading) over time.

You can simply take the difference of two kWh readings & divide by the fraction of the hour over which they were taken in order to get “average power”. Or you can approximate by sampling and averaging power over that interval (the more frequent the samples, and the more steady-state the power consumption, the more accurate the average).


#18

i see this too but i have always assumed it is because the generation samples and net consumption samples are slightly misaligned in time. couldn’t that be the cause?


#19

Unless you have something monitoring your net consumption and adjusting its load accordingly, generation and consumption should be totally decoupled, and you should not see such strong correlation between consumption and generation.


#20

i guess my point is that each consumption data point as presented by PVO is computed as the difference of the net consumption (from the smartmeter) and the generation (from the inverter), and so if the net consumption and generation data are not timestamped properly that you’ll see bogus swings in the instantaneous consumption.