Monitoring House Consumption with a Solar PV system installed.

[AlanIOW]

Hi

I keep getting asked how I monitor the House energy consumption on my system which is diplayed on PVOutput.org here;

http://pvoutput.org/intraday.jsp?id=2476&sid=1872

The solar generation is relatively easy and is measured with a Current Cost EnviR with an OptiSmart Sensor which counts the LED pulses on the Generation meter [Elster A100c]. The EnviR is connected to a permanently on PC which has PVOutput's Sevice Integration program installed, which is available on their website. This posts readings every 5 mins to PVO in Australia who turn the data into a fine set of graphs and system comparison tools.

To display house consumption is also not a problem when the Solar PV system is not generating, but when it is the EnviR will measure the net wattage which could be +/- but you don't know which. So here's the trick [Gleaned from a Navitron thread about 2 years ago];
Use a large Current cost CT Clamp connected to its own transmitter and place it around the incoming Live cable between the House meter and the Consumer unit, as you would normally for consumption. BUT also run through the same CT clamp the live from the inverter, but crucially this has to be twisted round so it goes through backwards. This removes the inverters output from the equation and you get a true reading for consumption. Obviously there are small errors involved with any of these CT clamps due to Volatage and Phase problems, but its not too bad at anything above 150W, I find.

Alan

I have knocked up a simple diagram below, I hope it helps;

[BruceB]

I think you have the inverter wire going the wrong way through the ct clamp.

As you have drawn it, when you are generating x kWh and with house consumtion of zero, so all the generation is being exported, then the ct clamp will be measuring 2x, not zero.

I am assuming you want it to measure actual house consumption.

Regards
Bruce

[AlanIOW]

Sorry Bruce, but you are wrong, with the reversed live from the inverter going through the same CT clamp as the incoming live cable the actual consumption for the house will show as zero in your example as the two will cancel each other out. I realize it sounds like it will not work, but if you think about it logically, it does.

The proof it works is, if you turn off the Inverter the actual house consumption reading does not change.

Alan

[JohnS]

Are you sure?

Let's assume house consumption 2 amps.

1 No PV. 
Therefore import everything.  Current through clamp is 2 amps left to right on incoming main.

2 1 amp of PV.  Therefore import 1 amp.  Current through clamp is 1 amp left to right on incoming mains and 1 amp right to left from inverter.  Total nil.

3 2 amps of PV.  Therefore everything consumed, no import or export.  Current is 2 amps right to left from inverter.

4 4 amps of PV.  Therefore consuming 2 and exporting 2.  Current is 4 amps right to left from inverter and 2 amps right to left export.  Total 6 amps

now let's change the inverter cable the other way, still assuming house consumption 2 amps.

1 No PV. 
Therefore import everything.  Current through clamp is 2 amps left to right on incoming main.

2 1 amp of PV.  Therefore import 1 amp.  Current through clamp is 1 amp left to right on incoming mains and 1 amp left to right from inverter.  Total 2 amps.

3 2 amps of PV.  Therefore everything consumed, no import or export.  Current is 2 amps left to right from inverter.

4 4 amps of PV.  Therefore consuming 2 and exporting 2.  Current is 4 amps left to right from inverter and 2 amps right to left export.  Total 2 amps

Any views?

[AlanIOW]

Are you sure?

No, not any more, you have raised doubts in my mind. But I am 100% sure what I have actually works and is accurate though.
I have always considered it this way; the reversed live from the inverter is acting like a neutral for the inverter and the Main live includes the Inverters live, so by combining the two it is completley removing the inverter from the equation, much the same as a CT clamp round a Live+Neutral gives no reading.

Or it could be my wiring is not what I thought, I'll have to have a look tomorrow.


Alan

[AlanIOW]

I have had another thought, when the inverter is generating the electrons flow in the other direction, so what is labled a LIVE is in fact the opposite. For example, when the inverter switches on, before any actual generation, the electrons flow into the inverter so the Live is a live, but when the inverter starts to generate the electron flow reverses, so the "LIVE" is now effectively a Neutral!!
 
Or is this too simplistic as we are talking AC and I am talking B*ll*cks

Any Thoughts?

[Parky]

It does sound a bit like b*ll*ocks to me - but them I'm a newbie to Solar PV, simply falling back on my basic knowledge of electricity as a ham radio operator many (many) years ago when  valves were still in fashion!. I'm sure I'll be corrected if I'm wrong, but live is live, whichever direction current is flowing in. Because it's an alternating current, isn't "live" just an indication of a potential voltage difference compared to something else - usually the earth? With AC I'd agree with other commentators that reversing a wire through a clamp would make no difference to the way a measurement is made. I thought these clamp detected the amount of current flowing through a wire, but not in which direction it is going.

I've not got any metering on my new system yet, and I may not even bother. But it seems to me you would need to have a clamp (or equivalent) measuring output from the inverter, and another measuring only the flow of current into the house at the fusebox. I thought I had my head around it when I saw page 10 of this wiring set up for a Wattson metering system, though the measuring equipment itself is irrelevant: http://www.diykyoto.com/store/assets/0000/0619/WATTSON_RENEWABLES_Eng_v0.5_low_res.pdf   With a Junction Box (Henley Block) in circuit you have a clampable wire to your consumer unit to measure total house consumption at any point in time, whereas on the other side of the block, current can flow in either direction, depending on whether you're generating lots to the grid, or taking lots from it.

With the left hand clamp positioned where shown in the diagram (ie on the inverter output) you would have a reading of solar PV yield at any point in time. The difference between the two readings (assuming it's accurately being measured) would give you an indication of consumption against generation at any given point in time.  - ie how much you are taking from the Grid. 
I can't quite work out what on earth you'd be measuring if you moved the left hand clamp to the other side of the junction box and kept the right hand one where it is -  this might give you . . .  a head ache.
It has me.
So I'll stand back and listen to what I've found to be incredibly informative advice from all the experts here. (Just don't listen to anything I say!)

[StationHouse]

Hi

I keep getting asked how I monitor the House energy consumption on my system which is diplayed on PVOutput.org here;

http://pvoutput.org/intraday.jsp?id=2476&sid=1872

The solar generation is relatively easy and is measured with a Current Cost EnviR with an OptiSmart Sensor which counts the LED pulses on the Generation meter [Elster A100c]. The EnviR is connected to a permanently on PC which has PVOutput's Sevice Integration program installed, which is available on their website. This posts readings every 5 mins to PVO in Australia who turn the data into a fine set of graphs and system comparison tools.

To display house consumption is also not a problem when the Solar PV system is not generating, but when it is the EnviR will measure the net wattage which could be +/- but you don't know which. So here's the trick [Gleaned from a Navitron thread about 2 years ago];
Use a large Current cost CT Clamp connected to its own transmitter and place it around the incoming Live cable between the House meter and the Consumer unit, as you would normally for consumption. BUT also run through the same CT clamp the live from the inverter, but crucially this has to be twisted round so it goes through backwards. This removes the inverters output from the equation and you get a true reading for consumption. Obviously there are small errors involved with any of these CT clamps due to Volatage and Phase problems, but its not too bad at anything above 150W, I find.

Alan

I have knocked up a simple diagram below, I hope it helps;

This looks so much cheaper than the Fronius monitoring solution 

Would you mind posting some pics of the various parts of your monitoring system so I can understand better?

Cheers

[AlanIOW]

I have had a look at the wiring of my system today and it looks like I was talking B*ll*cks all along. Bruce and John are correct in that the Live wire from the Inverter should go through the Consumption CT Clamp the other way, I have corrected my diagram below.



My apologies again to Bruce and John and anyone else I have told to twist the live cable round.

Parky - You are correct that with a single live cable through a clamp it does not matter which way it goes through, but with two live cables going through a single clamp the relative direction of the cables makes a difference in that the currents measured are either added or subtracted.


Alan

[AlanIOW]

This looks so much cheaper than the Fronius monitoring solution 

Would you mind posting some pics of the various parts of your monitoring system so I can understand better?

Cheers

You will need one of these;
 http://www.amazon.co.uk/Current-Cost-EnviR-White-Smart-R/dp/B004NCJOXK/ref=pd_cp_ce_3/280-0156156-6208013

and one of these;

http://www.amazon.co.uk/Current-Cost-OptiSmart/dp/B005IW0TS8/ref=pd_cp_ce_4


You will also need a permanently on PC if you want to monitor the system live on PVOutput.org like this; http://pvoutput.org/intraday.jsp?id=2476&sid=1872

Hope this helps

Alan

[langstroth3]

I assume your temperature data on the pvoutput site is internal house temp - it's a mild autumn so far, but not that mild!.

[StationHouse]

This looks so much cheaper than the Fronius monitoring solution 

Would you mind posting some pics of the various parts of your monitoring system so I can understand better?

Cheers

You will need one of these;
 http://www.amazon.co.uk/Current-Cost-EnviR-White-Smart-R/dp/B004NCJOXK/ref=pd_cp_ce_3/280-0156156-6208013

and one of these;

http://www.amazon.co.uk/Current-Cost-OptiSmart/dp/B005IW0TS8/ref=pd_cp_ce_4


You will also need a permanently on PC if you want to monitor the system live on PVOutput.org like this; http://pvoutput.org/intraday.jsp?id=2476&sid=1872

Hope this helps

Alan

Many thanks but I don't really understand the monitoring house consumption bit?

Cheers

[asorton]

Alan,

Big thank you for the info here and the PM's.

I had a monitor supplied by E-on over a year ago, I had no idea it was an enviR.

I already had good generation monitoring with Pv Bean Counter getting data by bluetooth and sending it to PvOutput.

Now with the EnviR plugged into my computer I have added usage and Temperature (although internal temp so not that useful) which PV Bean Counter uploads for me.

I now have to try and work a way to get both cables through a large clamp (and get a large clamp from some place?), only place I can think of that they are close together is in the CU itself and I'm not sure there will be room there so I'm not sure it can be done.

If I could find a dry outside location for the EnviR the temperature information would also be meaningful.

[Iain]

Hi asorton

The clamp doesn't always need to be on the live wire. It can go on the neutral if it is easier. I have my clamp on the neutral
http://www.navitron.org.uk/forum/index.php/topic,13839.msg174175.html#msg174175

Iain

[asorton]

Hi asorton

The clamp doesn't always need to be on the live wire. It can go on the neutral if it is easier. I have my clamp on the neutral
http://www.navitron.org.uk/forum/index.php/topic,13839.msg174175.html#msg174175

Iain

Thanks but I swapped two carriers so the inverter is right next the the mains in the CU.

Its to tight to get the regular clamp over the two wires so I have ordered one of these:



I hope that its small enough to fit in the available space.