Increase power consumption on sunny days

[jonplapham]

Hello-

I have a recent solar panel installation at my home in Rio de Janeiro Brazil. Specs: 9.6kWp, 24x 400W panels (Canadian Solar), 8.2kW inverter (Fronius 8.2-1). I have installed a Schneider Electric IEM3255 smart meter which measures power in/out of my house along with the built-in monitoring from the inverter.

I have noticed that there is a consistent increase (to a max of 1kW extra) in my household power consumption matching when there is solar power generation. On a sun-less day we do not see this increase, and on intermittent cloudy days this increase comes and goes with the sun.

In the attached images, green is PV gereration, yellow is overall household energy consumption as measured by the Schneider Electric IEM3255 independent of the rest of the system.

The first attached image (28052019) shows a typical sunny day while we are away at work, no one at home during the day. Our background electrical usage is around 1kW, which rises to about 2kW during the sunnies part of the day, then drops back down to 1kW when the sun goes away.

The second attached image (10062019) shows a cloudy morning, sunny afternoon.

The third attached image (04062019) shows a cloudy day with short bursts of sun. See how the consumption peaks match with when the PV gererates power.

Any idea on where this "extra" 1kW of power consumption comes from? Does the inverter use power when it is working?

Thanks for any help!
-Jon

 

[Scuba]

You said you fitted the meter but didn't say how it was fitted. Where are the CT clamps positioned?

 

[jonplapham]

The clamps are positioned on the wires directly from the meter on the street, so they measure both the house consumption and the PV injection.

I've attached a plot of the actual raw data from the previous 10062019 graph. Yellow is measured at the CT clamps, green is generated power from the inverter. Subtracting yellow from green produces the yellow line in the plot "smart_meter_10062019.jpg" above.

Note: I have access to all the measured raw data, currents, voltages, power, frequency, etc. If anyone is interested, I can make it available.

 

[jonplapham]

Just to make sure I was clear before, here is a screen shot of the schematic from the manual from the smart meter showing where it was installed.

 

[FatAlan]

It not your air con kicking in on a hot day?

 

[static zap]

No sneaky heater in your Hot water cylinder , turning on to soak up generated power ,(but panels have become shaded / inefficient !)

 

[littlespark]

If it’s anything like my energy monitor, it doesn’t know the difference between power used and power exported to the grid.
A CT coil just measures amps... it doesn’t know which way.

 

[jonplapham]

It not your air con kicking in on a hot day?

No, it is "winter" here in Brazil, a frigid 60-70f (15-22C) during the day. The AC has been turned off.

No sneaky heater in your Hot water cylinder , turning on to soak up generated power ,(but panels have become shaded / inefficient !)

No. Our hot water is a separate non-PV solar system, no electricity used.

If it’s anything like my energy monitor, it doesn’t know the difference between power used and power exported to the grid.
A CT coil just measures amps... it doesn’t know which way.

My "smart meter" measures (see the attachment smart_meter_10062019_raw.jpg) power entering as negative, and power injected to the grid as positive. I'm not sure how it does this.

 

[static zap]

You have multiple panels ,but do you have only 1 invertor converting PV energy from panels - to AC !

 

[jonplapham]

You have multiple panels ,but do you have only 1 invertor converting PV energy from panels - to AC !

Yes, only 1 inverter. It is a 2 string inverter, so there are 2 separate sets of panels.