Testing grid tied inverters

Hardware is easier and cheaper than software (more reliable, too).
With a clamp AC/DC ammeter, you can check output of each PV panel and each inverter.


Since your panels are accessible, on a patio structure not house roof, I'd consider rewiring them in series/parallel strings and buying a used or new-old-stock string inverter.

diWhy said:

Ok, but does this mean the panel outputs DC or does it actually have microinverters built into the panel itself so it's output is actually AC?
That would be confusing to me since the input of the inverters are 48V DC.

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The panels make DC volts. The raw/wild DC goes to the junction box “internally” with probably some diodes and maybe a parallel connection (probably not) and the output wires are feeding microinverters that take the DC and make it AC voltage. That is effectively the “panel output” but the DC wires between JB and micinverts can be used to measure panel efficacy.

If you have good DC but no AC-out, then THAT indicates a likely bad microinverter.

(It is possible though unlikely to have full VOC from the panel but if panel has/had a failure or the JB had water in it you won’t achieve any amps because as soon as a load is applied - microinverter- the volts plummet and maybe only milliamperes pass. But ignore that for now as it is unlikely)

If you have poor DC then it’s panel, JB, or cable/connector issues.

Likely you’ll have good DC and a bad microinverter.

Don’t forget these things can kill you.
Don’t let yourself be a conductor.

diWhy said:

Restarting it changes nothing, sunny days or nighttime changes nothing,

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Which is what I’m saying.
Your charge controller and/or monitoring system is whacked

.

12VoltInstalls said:

If you have good DC but no AC-out, then THAT indicates a likely bad microinverter.

(It is possible though unlikely to have full VOC from the panel but if panel has/had a failure or the JB had water in it you won’t achieve any amps because as soon as a load is applied - microinverter- the volts plummet and maybe only milliamperes pass. But ignore that for now as it is unlikely)

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Good Voc isn't necessarily proof panel is good. I've measured good Voc and Isc, but an intermediate voltage & current were low.

https://diysolarforum.com/threads/measuring-pv-panel-performance.27932/

12VoltInstalls said:

If you have poor DC then it’s panel, JB, or cable/connector issues.

Likely you’ll have good DC and a bad microinverter.

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If one panel outputs AC (seen with clamp ammeter) but neighboring one does not, could swap PV panel connection to see which part doesn't work.
Cover PV panels with opaque material while swapping MC connectors to prevent arcing. DC voltage will remain high enough to shock, but current will be far lower.

>Hardware is easier and cheaper than software (more reliable, too).

Yes but hardware has to be programmed and sometimes, it's useful to do it yourself if you can because you can get more out of the data.

>With a clamp AC/DC ammeter, you can check output of each PV panel and each inverter.

I do have a clamp meter, I think I just don't know quite what I'm looking for. I mean, I can see the voltage when I clamp over a wire and if I move it around, the voltage changes. I'm not used this kind of measuring much in my life so am not sure what to expect. Just need more experience using that method.

>Since your panels are accessible, on a patio structure not house roof, I'd consider rewiring them in series/parallel strings and buying a
>used or new-old-stock string inverter.

The rear 7 on each major section are easier to get at but the rest aren't so easy. I was trying to think of a way to tap into everything while I'm up there so I could get direct readings from every component, each panel and each inverter because of how hard it is to get up there. I just don't know how much I trust the manager or PLC for that mater when things start breaking down.

My thought was to mount panel boxes here and there where each wire would terminate onto a clean setup that I could easily reach to test when needed.

diWhy said:

The panels make DC volts. The raw/wild DC goes to the junction box “internally” with probably some diodes and maybe a parallel connection (probably not) and the output wires are feeding microinverters that take the DC and make it AC voltage. That is effectively the “panel output” but the DC wires between JB and micinverts can be used to measure panel efficacy.

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Ok, thanks for confirming that. I thought I might be being told something else .

>If you have good DC but no AC-out, then THAT indicates a likely bad microinverter.

Well, this is where I'm still in an unknown.
Since the inverters are grid connected, there is always 120VAC on each leg so I guess I need to measure the current. Since I should not disconnect and re-connect the panel while there is power from the inverter, it's not clear to me how I go about this. Sorry but someone explaining it face to face, I'd get it immediately but using text is making it a lot more complex than it actually is and will be once I know what I'm doing.

>If you have poor DC then it’s panel, JB, or cable/connector issues.

I can can test each panel once that meter I ordered gets here.

>Likely you’ll have good DC and a bad microinverter.

Still not clear how I can confirm the inverters are working or not since they are grid connected so always have AC on their output side.
As mentioned, some of them are making a really loud buzzing sound so I assume more have or are about to fail.
I also assume there is no fire hazard to worry about since the system is using heavy shielded cabling and the inverters are sealed in metal canisters. I'm assuming that because everything would have had to pass standards and I'm in a serious fire zone area.

>Which is what I’m saying. Your charge controller and/or monitoring system is whacked

I must have missed something. I have DC to AC inverters. What charge controller are we talking about?


If someone still wants some pics from underneath, I can do that. It's just that they aren't going to show anything more useful then the docs I shared which clearly show how it's wired up.
I forgot I had taken a little drone footage so see what trellis panels I needed to fix as they regularly break so here are some caps to show what I mean by canopy.
At the back, things are easy to reach, at the front of each section, it's one heck of a challenge as it is very steep rocky sand and very tall at around 16 feet at the high end.

Clamp meter can only read amps. Needs to be around a single wire, not a pair of wires.

On an AC wire, you know that is at 120Vrms or 240Vrms.
PV panel, it is an unknown DC voltage. but given watts AC and amps DC, voltage can be calculated.

What you're looking for in microinverters that produce different current/watts compared to others.
Then with swapping of wires, you can determine if PV panel or inverter is faulty.

>What you're looking for in microinverters that produce different current/watts compared to others.
>Then with swapping of wires, you can determine if PV panel or inverter is faulty.

Ah yes, note down each, looking for variations on the output side. I think that was mentioned but a bit lost by me somewhere.
While trying to learn how to figure out my system, I've also been under pressure with a computing center upgrade.

Any chance someone knows of some couplers I could get for both the mc4 panel connectors and these 4-wire ones?
I'd like to put something together as mentioned in my previous message that would give me a two wire output that I could run to a panel box that I could reach. That way, I could test all of the panels and inverters more easily.

diWhy said:

I mean, I can see the voltage when I clamp over a wire and if I move it around, the voltage changes.

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That’s amps

diWhy said:

there is always 120VAC on each leg so I guess I need to measure the current.

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yes. The warp of the clamp meter measures current by induction.

diWhy said:

Which is what I’m saying. Your charge controller and/or monitoring system is whacked

I must have missed something. I have DC to AC inverters. What charge controller are we talking about?

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Forget the charge controller mention. That was referring to the microinverters handing off info to your monitoring software. Which is whacked out if it shows watts after dark.

Hedges said:

What you're looking for in microinverters that produce different current/watts compared to others.
Then with swapping of wires, you can determine if PV panel or inverter is faulty.

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He uses less words than me but says plenty

Ok, it will be several days before I can get to the next step. I need someone with me to block the panel while I'm underneath the canopy and the meter I ordered has not come in yet.

What I think may be difficult/inconvenient is that AC wires are probably a pair in a cable, so clamp ammeter will read zero. It needs to be around a single conductor. This would have been an easy way to definitively measure power per panel.

What you can do easily is measure DC current on PV wire. Probably that will correlate well with power, but possibly not. If one out of three diode-bypassed sections of panel was bad, you could read same current, but voltage and power would be only 2/3 as much.

If you get MC4 Y cables, then (with panel shaded), you can insert these cables giving DMM access for voltage as well as clamp for current. Get an MC4 tool as well; it gets old trying to open those with bare fingers.


If a similar breakout cable for the AC connections is available you might be able to measure with it. An extension cable, if you peeled off the outer jacket, you could separate insulated wires to fit clamp meter.

Yes, I bought a current meter and cables to tap between the panel and the inverters (H4).
Each of the inverters has a Y cable that is connected to the next inverter so there are no free plugs. However, I made up a connector so that I can tap into the output so could clamp on those wires. I'll have to look at it again to see how I can tap in while each inverter remains connected to the grid.

Turns out I do have full access to the manager. Just never noticed you have to stop data collection to get access to the rest.
Anyhow, I re-discovered all of the modules and only 38 of 32 installed were found and all of them show 0 CD volts.
For status, all the manager shows is what you see in the image, IEEE-1547.

It's almost as if the inverters are simply not communicating properly anymore. I know the system is not generating anything but maybe there is some sort of shutdown function in the inverters that was set by the installer before they left me with this. More likely, the manager is simply not working right.

Does anyone know of any sort of generic PLC reader that would show me what's going on with each module/inverter?

I would test the panels and micro’s and see what that tells you. Didn’t you say you had spares? If one fails out in test, put in anew one and test.
I feel like you’re ocd on the software but nobody here can tell you how to hack it. But a thousand people can deal with the panels and microverts and get you functional

Yes, I'm still going to test the panels and inverters as soon as I can get out there with help.
I was just playing around with the manager while working on other things.

OCD on the software? Kind of, just because I want to understand all of the pieces I have in this system.
I have full access to the entire manager at this point so not really focused on that too much. Just wanted to see if the manager could help discover the inverters and provide some additional information. Never hurts to have more info than you need.

So yes, I was focused on the manager and still am so OCD for sure .
I still plan on getting up there but messing with the manager is something I can do from my desk.

It turns out, they trashed the operating system somehow. There were entire directories removed, permissions messed up. I'm not the paranoid type but I'm not sure how an embedded system could do that to itself considering it basically just resets back to defaults on each reboot. I build IOT devices so am very aware of how embedded operating systems work.

Once I noticed that, I fired up another manager and started working through the directories being careful not to overwrite anything that is unique to this manager since some things would be different. After a couple hours of copying programs back, checking permissions etc, I restarted the system and here is the result.

It's 9am so the sun is not over the full canopy but the watts keep going up. It's now at 1600 watts as I write this.

I did a full discovery of the inverters and it found 38 of the 42 installed so definitely have some bad ones which I'll find when I get up there. I hope it's not panels because that will be harder to fix. I've yet to find any used/spare panels.

We'll see how high the wattage gets during the day but at least I can see something now which is positive to me.

sounds like your making progress.

never underestimate the ability of something like a lighting strike or something to erase some random data.

I've never seen lightning remove directories on an embedded system but I've seen plenty of lightning damaged hardware.
The directories removed were the ones that the startup program needs to start all of the PLC code.
Really not sure what's happened here but happy that I've now got a couple of tools to help me with the system.

I very much wanted the manager back because now I have two different ways to see the system.
I can now see the output of each inverter that showed up. I can see the DC, the AC and the temperature of each.

Once I get up there, test and get the serial numbers, I'll be able to associate what is what and rebuild the rest of the manager too.

The thing that has me a little perplexed however is why the power company meter was always showing Er and no power being generated and now that the manager is partially working again, that same meter is reading output. That's a bit odd. It should have been seeing output no matter if the manager was working or not but it definitely wasn't.

It will be interesting to see if this generation is reflected on the next bill.

If it is, it means the manager is somehow involved in feeding the meter perhaps. I'll have to take a closer look at how things are wired up. That doesn't make any sense. Or maybe the manager is somehow controlling the inverters but I doubt that too. I think they only output PLC data. However, there is a ping function which means there's a slight chance they do respond to certain commands and it's not documented.

diWhy said:

If it is, it means the manager is somehow involved in feeding the meter perhaps.

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As a concept I know that the Enphase Envoy can be programmed for Zero Export. It needs the Current Transformer on the Envoy and presumably some software setting which then calculates output at the grid interface and modulates the micros accordingly. Perhaps there is something similar with your system?

Ampster said:

As a concept I know that the Enphase Envoy can be programmed for Zero Export. It needs the Current Transformer on the Envoy and presumably some software setting which then calculates output at the grid interface and modulates the micros accordingly. Perhaps there is something similar with your system?

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Yes, to me, there is something that is undocumented.
First of all, the inverters respond to ping and status requests which means to me it's possible there is some sort of basic receiver on the inverters.
Somehow, the manager is involved in what is going on, perhaps controlling the output along with the inverters knowing to shut down when grid goes down.
Today is a very sunny day and the system is generating only 2100 Watts. It should be around 6K to 9K but it's not.
There is no reason that 38 inverters aren't outputting but here's the fact that has me perplexed.

Notice in the following image that the output view shows 0 watts. I think the output is turned off but the inverter is working fine.

Yet the inverter can be reached and is showing DC volts in of 32.36V.
A valid input range is 18V-37V which means the inverter is within range so why is it showing 0 watts output?
In fact, many of the inverters showing 0 watts also show a valid DC voltage.

I'm starting to think that the real reason these micro inverters were flawed is not because their hardware is dying but because their software has problems and is preventing the output from happening. I think most of the inverters you see as 0 watts are actually good but they aren't outputting their AC due to programming, nothing else.

Hopefully, it becomes clearer why I was and still am so OCD about the manager .

I have limited understanding of the grid tie micro inverters. however several? of the systems use the grid frequency as a controlling attribute. FOr instance, I know you can shutoff enphase micros by ramping the frequency out of range of what they expect to see. (as I understand it) this means they could effectively be reporting the correct DC volts (ie the panels see sunshine) but they choose not to output any of it because controlling software is saying not to.

As far as I know, all micro inverters work roughly this way. they all rely on a central command and control unit to organize and centrally tell all the micro inverters what to do.