Monitoring Solar + Electricity with 2 phases

bgregster · 2020-09-04T13:30:30.226Z

Hi,
I am using 2 of my 3 phases and one of them is connected to my solar array.
To help me buy the right kit, can someone confirm for me these assumptions - the solar monitoring kit will give me:

Monitoring of phase 1 electricity import with one of the CT clips
Monitoring of phase 2 electricity import + export with the second clip
Monitoring of the Solar generation via the optical sensor (my solar meter has an LED that flashes according to throughput)
All data stored online via wifi connection to router

I’m also hoping that I don’t need advanced skills to set up and access the data flowing in. I use Mac OSX to access the internet and have enough knowledge to follow some basic set up commands if required (like maybe an online admin console) but would that be enough?

Robert.Wall · 2020-09-04T14:13:45.672Z

The emonPi you’re going to buy How open is my data? Can I download or record it into, say, Google Drive? is designed for the normal domestic UK single phase supply.

The emonPi can only measure the voltage of one phase, and only calculate real power on one phase. So you’ll get wrong answers if you put a c.t. on the second phase. What you propose won’t work.

For what you want, I’d recommend an emonTx with the 3-phase PLL software (to upload that onto an emonTx to replace the default software, you’ll need a programmer from the shop) and an emonBase instead of the emonPi.

You’ll then have 4 c.t. inputs (one is more sensitive low-current), each of which you can allocate to whichever phase you choose. Because, like the emonPi, the emonTx has only one voltage input, it relies on all phase voltages being the same as the one it’s measuring. If the second phase voltage is significantly different, that’s a source of error. You can still have the optical pulse sensor on you generation meter, or you can have a c.t. or both.

I’ve already explained that your data is stored on the emonBase - because an emonBase is an emonPi without the analogue energy measuring part - so you store it “online” as well.

We have instructions for setting up the Arduino IDE that you’ll need to change the software on the emonTx in the ‘Learn’ section, you can look at those and download the sketch from Github to see the sort of stuff you’ll be handling. I presume you’re OK with editing text files, saving them, etc, and typing console commands?

bgregster · 2020-09-04T15:18:06.178Z

Hmm, that seems to add quite a bit of cost and complexity.
So follow-up questions are required:

If I just measured one phase, and compared that with solar production (using optical sensor), would that give me the correct info (just missing whatever the 2nd phase was importing)? I guess I just don’t understand why a second sensor couldn’t just pick up that 2nd phase and add it to the data separately.
The solar kit included an AC sensor. Would I not need that too? (TBH I haven’t grasped what this is for).
If i have to buy a programmer too, is this required for software or firmware updates? Would I not need that anyway on the emonPi?
I saw some articles about using a wifi adapter instead of emonBase providing I don’t need SD storage. But I can’t find this option in the shop.
Finally - the diagram indicates that the the emonBase is connected to the emonTx but not it’s own power supply. Is that the case?

Robert.Wall · 2020-09-04T19:41:48.334Z

bgregster:

If I just measured one phase, and compared that with solar production (using optical sensor), would that give me the correct info (just missing whatever the 2nd phase was importing)? I guess I just don’t understand why a second sensor couldn’t just pick up that 2nd phase and add it to the data separately.

It’s because you have a three-phase supply. Each of the three voltage waves are displaced by 16.667 ms relative to each other. To measure the power, your emonTx/emonPi samples each voltage and current wave about 2500 times per second, multiplies each pair of samples together to get the power at that instant, then averages all those readings of power. If you’re multiplying the current by the wrong voltage, you get the wrong answer.

bgregster:

The solar kit included an AC sensor. Would I not need that too? (TBH I haven’t grasped what this is for).

It’s to provide that mains voltage sample, and you will need one, whether you have the emonPi or emonTx. But the emonTx does not need the separate d.c. power supply.

bgregster:

If i have to buy a programmer too, is this required for software or firmware updates? Would I not need that anyway on the emonPi?

Yes to the first, no to the second. What I should have mentioned before was that by making a wired serial data connection between the emonTx and a Raspberry Pi, you would not need the RFM69Pi adapter that makes the RPi become an emonBase.
You might not need the programmer if you have that serial connection. There’s new software out (I’ve not tried it yet, so I can’t say how straightforward or otherwise it is). The emonBase/emonPi is controlled and set up via a web browser.

bgregster:

I saw some articles about using a wifi adapter instead of emonBase providing I don’t need SD storage. But I can’t find this option in the shop.

Here it is.You will need a separate 5 V d.c. power supply as well as the a.c. adapter with that, due to the additional power needed for Wi-Fi.

Where are you going to run emonCMS - assuming that’s what you want to use to record and view your data? You need a web server that’s continuously available to receive the data as it comes in.

bgregster:

Finally - the diagram indicates that the the emonBase is connected to the emonTx but not it’s own power supply. Is that the case?

I can’t think which diagram that would be, but no, both need a power source - the interconnection is normally by radio (the RFM69Pi adapter actually receives and turns the radio packet of data into a serial stream for the RPi). Normally, the emonTx is powered from the a.c. adapter, whilst the emonBase needs a 5 V USB power supply. If you do have a serial connection, while both can share a power supply, you still need the a.c. adapter to measure the voltage. The a.c. adapter cannot power the RPi.