Monitoring House Consumption with a Solar PV system installed.

[AlanIOW]

These type of statements from 'knowledgeable' people only serve to confuse readers who don't have a full understanding of the technicalities.

I think it is you who don't have a full understanding of the technicalities. The system does work and it does give a fairly accurate indication of CONSUMPTION. It is not meant to measure the NET, that is calculated on the PVOutput website from the Generation and Consumption figures.

If two wires cannot add or subract, then can you explain why a CT clamp around a Live and Neutral gives no reading!!

I do not profess to be an expert or even a knowledgeable person, but i do know 100%, it works.

Alan

[pj]

These type of statements from 'knowledgeable' people only serve to confuse readers who don't have a full understanding of the technicalities.

dominator99 - you are guilty of the very crime you are trying to expose.

CT's pick up the weak alternating magnetic field surrounding the conductor induced by the current flow. That is used to generate an alternating voltage that is proportional to the current flow. With two conductors, if the AC in both is in phase, then the magnetic field will be doubled. If the AC in each is 180deg out of phase, the net magnetic field will be (almost) zero (or cancelled). (assuming equal absolute current flow in each case)

CT's are sensitve to the direction of current flow, the voltage waveform they produce could be used to calculate the direction of the instantaneous current flow. More importantly, however, they are not sensitive to power flow - for that you need to know the relative phases of both current and voltage.

In a power monitor, the electronics take the output of the CT which is a voltage waveform proportional to current flow, integrate over time to produce a current consumption, then assume a 240V voltage, and produce a power figure. They do not attempt to indicate direction of power flow - I agree they are incapable of doing that from just the CT output.

Hopefully I haven't confused anybody, and am happy to be corrected if I've misunderstood anything.  

[asorton]

Just came across this post & would like to clarify the question of using CT's to monitor domestic electricity useage.

A common misconception seems to be that CT's can measure current flow direction - they can't.  They CAN measure current (that's what they're designed for, albeit inaccurately) but NOT the direction it's moving ie import from grid or export to grid.
So running grid AC mains & PV AC live conductors through the same CT won't result in addition or subtraction of currents as suggested but will always ADD the 2 currents together.

These type of statements from 'knowledgeable' people only serve to confuse readers who don't have a full understanding of the technicalities.

I monitor my PV system using CT's & can assure readers that whether I'm importing or exporting a given amount of power, the software shows this same amount of power being processed (but not very accurately).  Only the spinning wheel of my electricity meter shows me whether I'm importing or exporting.

EmonTX can measure which way current is flowing & I believe they will shortly be available for sale on openenergymonitor.org

If this does not work please explain my live graph: http://pvoutput.org/intraday.jsp?id=4601&sid=3641&dt=20120126

The day shown is a good example as its a high generation day & I went out to work at 9.00AM & came home at 5PM, look at the steady consumption line despite 10kwh generation & you have seen a picture of my clamp with both main tail and inverter live running through it.

before this setup it could be showing:

500w - no generation but using from the grid
0w - 500w generation and nothing from grid
or 1kW - 1.5kW generation with 1kW being exported

it was all over the place up & down yo-yo.

You might not think it works - but I say the proof is in the pudding!

[ericw]

These type of statements from 'knowledgeable' people only serve to confuse readers who don't have a full understanding of the technicalities.

dominator99 - you are guilty of the very crime you are trying to expose.

CT's are sensitve to the direction of current flow, the voltage waveform they produce could be used to calculate the direction of the instantaneous current flow. More importantly, however, they are not sensitive to power flow - for that you need to know the relative phases of both current and voltage.

In a power monitor, the electronics take the output of the CT which is a voltage waveform proportional to current flow, integrate over time to produce a current consumption, then assume a 240V voltage, and produce a power figure. They do not attempt to indicate direction of power flow - I agree they are incapable of doing that from just the CT output.

Hopefully I haven't confused anybody, and am happy to be corrected if I've misunderstood anything.  

I concur with PJ, you can measure the direction and magnitude of power flow with a single CT but you have to make your measurement in a phase sensitive manner, not just simply measuring the magnitude of the output current

[Summerdays]

Asorton you are obviously measuring (clamping) different wires than we are . Here is our output for today showing our consumption:

http://pvoutput.org/intraday.jsp?id=2202&sid=1647&dt=20120201

I wanted it set up so that I could see when we went off grid on a sunny day, but we can't tell how much of the solar we are using once we are on PV electricity only.

[asorton]

Asorton you are obviously measuring (clamping) different wires than we are . Here is our output for today showing our consumption:

http://pvoutput.org/intraday.jsp?id=2202&sid=1647&dt=20120201

I wanted it set up so that I could see when we went off grid on a sunny day, but we can't tell how much of the solar we are using once we are on PV electricity only.

I have mine as Alan recommended in post #8 of this thread and it works a treat, I posted a picture of how I managed in in post #23.

If you can achieve this I think you will get the results you want.

[AlanIOW]

Hi

As Tony says, if you can manage to get your CT Clamp to measure the True Consumption, then you can use PVOutput to graph almost anything. The above image is a combination of Generation (Yellow), Consumption (Red) and Net (Blue) which obviously changes from - to + when the generation kicks in unless someone fires up the kettle as at 1.00pm ish. The image is from 2 PVOutput screenshots mashed together in Photoshop.

Hope this helps

Alan

[Summerdays]

For me the way that my husband has set up the clamps at the moment is better as I want to be able to look at the graph and see clearly whether we are powering the house (except for the heating cycles of dishwasher/washing machine or the other high users such as the kettle/oven as we don't have enough panels to achieve that) so that I know when to put on those higher users. I love seeing that flat line along the bottom

[Ben55]

Dominator barged in, adding confusion...

Without applying the principles of electromagnetic induction.

Thankfully you guys have corrected him.