Monitoring DC power from PV strings cables to Inverter

[fritserasmus]

I have two SMA SB 4000TL 21 inverters. Each has two two MPPT controllers and I also have 2 strings of PV arrays connected.

I therefore have 4 arrays feeding into the two inverters. Two are facing East and Two are facing West and the two Eastward facing arrays differ in size.

I would like to monitor the power production PER array.

Using the emonPi and emonTx with 4 CT sensors, can I monitor production per string? ( https://shop.openenergymonitor.com/emonpi-2/ ) + ( https://shop.openenergymonitor.com/emontx-v3-electricity-monitoring-transmitter/ )

This power will be DC and ideally I would like the numbers to add up. So: adding these 4 lines power production together, should match the inverter output production.(which I am measuring at present)

The reason I want to measure these lines is to identify any abnormalities as early as possible.

Your advice and or comments will be appreciated very much.

(As a side note: I would like to mention I am using SBF Spot (  https://github.com/SBFspot/SBFspot  ) log the power production and feed to PVOUTPUT.ORG) These reading are NOT fed to an emonCMS database though. It also sends ONE reading per inverter to PVOUTPUT and not a reading per line)

Regards

Frits

[___]

6 minutes ago, fritserasmus said:

Using the emonPi and emonTx with 4 CT sensors, can I monitor production per string?

I don't know emon that well, but from what I remember, this will work for measuring the AC production.

7 minutes ago, fritserasmus said:

This power will be DC

Can't measure DC with a current-transformer. Your best bet would be a hall-effect current sensor, something like the Allegro ACS712 chip. Gives you a galvanically isolated way to read a voltage of 0V to 5V corresponding to the current passing through the other end. But you'd also have to monitor voltage as the MPPT would move it up and down and the instantaneous power would depend on whatever V is at that point in time. Probably easier to measure this on the AC side, which is what I assume you wanted to do anyway.

Alternatively... the SunnyBoys speak SunSpec, and the registers you need to query is pretty standard. For the cost of one RS485->USB converter and a bit of pythony modbusy goodness you can daisy-chain the lot and ask the inverter what the numbers are... :-)

[fritserasmus]

12 minutes ago, plonkster said:

Allegro ACS712 chip

Like this: https://www.lazada.com.my/usb-to-rs485-485-converter-adapter-ch340g-chip-23021431.html

11 minutes ago, plonkster said:

Probably easier to measure this on the AC side, which is what I assume you wanted to do anyway.

Correct. I want to know DC; what is production.

12 minutes ago, plonkster said:

RS485->USB converter

As you said: This is probably easier: BUT will I be able to feed readings into an emonCMS? - (Steep learning curve here for me!) :-)

 

[Sidewinder]

@fritserasmus, I agree with your requirement. 

I just think trying to MEASURE the DC current/Voltages of each string should almost be your last resort.

I don't know the SMA's from a bar of soap, , but I would hope that it has a comms port, like most modern Inverters, and over it is spews out a continues streams of data. I suspect this to be problematic, as you are already using the comms port for SBF Spot export.

Hopefully this is the case, and buried somewhere in there and de-cripting the protocol, the PV strings info, just like what @Manie's done with Axperts/ICC, which you are familiar with, 

Maybe somewhere someone has done something similar.

But wouldn't it be nice is one can use ICC to monitor any inverter with a Comms port. Just select the correct one.

 - Now I see @Manie pulling out his hair, the few he has left, as he probably has lost a few in just trying to keep up with the Voltronic's range available in RSA, because every few weeks, I see a new version pop up. which reminds me, I'm about 3 version behind.

But these day's, the whole world's your market. He's got a very decent product, maybe it's time to take it to the next level 

I have in the recent weeks, discovered that one of my strings was misbehaving, as in Zero output. So if I didn't have ICC, i would have never picked it up. I could see 124 Volts from the string, with 0 Amps, so I knew it is not the string, but the inverter misbehaving. I initially thought that a fuse (20A) had popped, as I upgraded the system this Winter, and haven't gone through a full summer yet. While I was at it, I used the opportunity to clean out the fuses and CB's etc, as I have been busy knocking a hole in the wall to install a extraction fan, as the temps in the inverter was approaching 50 Deg C. 

 

[Sidewinder]

From a quick Google I can see that SFB Spot "sees" the following values that it uses to get info into pvoutput.org.

//valuetype
	//0x2601=Total Yield Wh
	//0x2622=Day Yield Wh
	//0x462f=Feed in time (hours) /60*60
	//0x462e=Operating time (hours) /60*60
	//0x451f=DC Voltage /100
	//0x4521=DC Current /1000

 

So look's like it's all there. I would think that if you use Arduino to do this, then you may just be in luck getting values store into EMONCMS. Thanks exactly what I've been doing with my geyser temps. But i read you're using a RPi. More reading then....

[maxomill]

hi there

I have 1 big array  which is divided into 3 and 1 west facing array for more afternoon sun  . I have a energy monitor  measuring all the solar panel dc power as the 4 are all in parallel . but with 4 disconnects so that I can  switch on/off  and  see any abnormalities  .

I like keeping  panels in equal numbers . it may costs a bit more on wiring  but you can easily check for discrepancies and faults  .

and no I cant monitor it on the computer so it may not help you but its a solution of some sorts

cheers

 

[fritserasmus]

3 hours ago, Sidewinder said:

@fritserasmus

 

I don't know the SMA's from a bar of soap, , but I would hope that it has a comms port, like most modern Inverters, and over it is spews out a continues streams of data. I suspect this to be problematic, as you are already using the comms port  SBF Spot export.

@Manie

@Manie

 

@sidewinder, the SMA's do not have a comms port as suggested. :-(

I am using the built in BlueTooth connection from SMA and Pi to establish the communication.

No wires between the Rasberry Pi and and the two SMA's .

 

I still have to check this suggestion: RS485->USB converter  of  @plonkster

[fritserasmus]

3 hours ago, Sidewinder said:

From a quick Google I can see that SFB Spot "sees" the following values that it uses to get info into pvoutput.org.

//valuetype
	//0x2601=Total Yield Wh
	//0x2622=Day Yield Wh
	//0x462f=Feed in time (hours) /60*60
	//0x462e=Operating time (hours) /60*60
	//0x451f=DC Voltage /100
	//0x4521=DC Current /1000

 

So look's like it's all there. I would think that if you use Arduino to do this, then you may just be in luck getting values store into EMONCMS. Thanks exactly what I've been doing with my geyser temps. But i read you're using a RPi. More reading then....

Having to purchase a Arduino to achieve that goal is a cheap run.

@Sidewinder, I know I cannot bribe you with a bear :-), but how many coffees and Cokes for some pointers and help me to manage to feed readings into ICC EMONCMS? :-)

[fritserasmus]

35 minutes ago, maxomill said:

hi there

I have 1 big array  which is divided into 3 and 1 west facing array for more afternoon sun  . I have a energy monitor  measuring all the solar panel dc power as the 4 are all in parallel . but with 4 disconnects so that I can  switch on/off  and  see any abnormalities  .

I like keeping  panels in equal numbers . it may costs a bit more on wiring  but you can easily check for discrepancies and faults  .

and no I cant monitor it on the computer so it may not help you but its a solution of some sorts

cheers

 

Maxomill, well, I have the STD feed into SMA site , but I actually would like to add graphs to the EMONCMS screen graphs, so I can pick irregularities up as it happens.

I also have 4 DC switches, that I can flip, but I prefer the computer Monitoring route

[Sidewinder]

I can't bear any beer's......

The arduino to emoncms is the easy part.

The construct is:

http://ipaddress/emoncms/input/post.json?node=1&json={power1:100}&apikey=apikey

ipaddress is your pi ip address or localhost, node=1 is the node where it will write the data to, so use something else, else it will add it to your ICC database, which is node 1. So just use 2

power1 is the name of the field it will create, and 100 is the value it will store.

Obviously, APIkey is your key from PVOutput.

For more help goto your emoncms, setup, Input API Help (top right corner).

Getting the string from your SMA via BT into the Arduino will be the trick.

 

[fritserasmus]

2 minutes ago, Sidewinder said:

The arduino to emoncms is the easy part.

 

Ummmmm, Ummmmm,......think...think..... How do I get the readings INTO the Arduino?

CT scanner?

Then this will be much simpler:

https://guide.openenergymonitor.org/setup/emontx/

[___]

Okay, I see from the spec sheet that this inverter does not have an RS485 connection, it is an optional extra. So forget about that (or find out what it would take to add that option).

Just measure the power output on the AC-out of each inverter and be done with it.

[Sidewinder]

AFAIK, CT scanners only works on AC, as mentioned before

• CT 1-3 are standard 100A / 24KW max CT inputs (@240V)
• CT 4 is a special high sensitivity input for 19A / 4.6KW (@240V)
• Recomended 100A SCT-013-00 CT sensors should be used

[fritserasmus]

So I guess my best bet would be to try and get the SBF Spot (  https://github.com/SBFspot/SBFspot  ) to make available the readings for emoncms ........mmmmmmm but how?

If it can send to PVOUTPT.ORG....there must be a way to send the readings to emoncms: OR am I over optimistic here?

 

[___]

The way we deal with PV-inverters that don't do Sunspec (or Fronius WebAPI) on a Victron system, is to use a current sensor (effectively a current transformer) to measure their output. You can also use a modbus power meter, like the SDM120 or SDM220, or you could use a Carlo Gavazzi ET340 (a three phase meter), and put your two inverters on separate phases. The SDM meters are quite cheap on ebay and ali-express. The CG meters start at around 1k for a ET112 single phase meter.

[fritserasmus]

@plonkster Thanks for that advice.

I am now making good progress in harvesting info.

I am ultimately aiming to build a more sophisticated system to divert access power to geysers in turn.

Like this just two notches up:  http://mk2pvrouter.co.uk/