Testing grid tied inverters

I searched the net and read a number of posts but nothing gave me a clear ok to go ahead so I thought I'd sign up, say Hi and ask my first question.

About three years into owning this system, it started having problems. The installer eventually left me hanging so now I'm wanting to learn what ever I can about it so I can maintain it myself.
At the time, I wasn't aware enough to know that I had gotten a grid tied system so the two things I'd like to do are to first fix the system and second, add some hardware so I can run this even when there are grid outages.

Step one is to test all of the inverters. Since it's a grid tied system, so long as the grid panel breakers are on, there is always 120VAC on each side.
If I understand correctly, to test, I have to turn off the breakers, then disconnect the inverters from the panel, inject voltage and see if I get a reasonable output.

The inverters are Pantheon II, Integrated, Microinverter, p250lv-208/240, 48V version.

Recommended STC Module input Power rating: 235 W – 280 W
Maximum Continuous input Power: 250 W
Maximum input voltage: 48 v
MPPT voltage range: 18 v – 37 v
Maximum Power voltage range: 25 v – 37 v

My question is, what exactly do I need as a 48V power supply to test these inverters?
I read a bunch of posts and it seems I need to use a range within the MPPT and not 48VDC.

Initially, I thought I should use a 48VDC supply around around 3 Amps to keep it under the 250 Watt max input.

I would start with an aggregate measurement first. An AC ammeter when the system is running would allow you to see what the output is. Better yet would be one that could convert to kWhs so you could get a daily output and compare that to an estimate from PV Watts.

If I understand you, you want to test your micro inverters. Is the panels on the roof? If you can get a DC clamp on amp meter on the PV wire from the panel, you can see what amps are being pulled.

What type of problems are you having? Do you have anything that monitors production ?

Most micro-GT inverters have a communication link system. Your Pantheon II, Integrated microinverter communicates with data over the AC lines from micro-inverters. If you don't have the comm head-end unit you should purchase one so you can monitor each panel performance.

Hi,
First of all, thank you for the replies. I am really feeling alone on this task so being able to use forums should help me get to something positive.

Pursolar, my installer, left me hanging with a messed up manager which is a solar bridge manager. I know about the admin/admin to get into it but there is another level needed to set some higher level things and he won't give me the password. I was able to gain access to the Ubuntu operating system of the manager but that's not helping much. It is not set up right, the module numbers are all messed up, etc etc. I need to gain access to the GUI to fix this mess since they won't bother to do it.

About three years into the ownership, the system started having problem after problem. At first, they would send someone and spend lots of hours working on it but within that three years, told me that mage parts were no longer available and that the inverters were now no longer manufactured.

I've had it about 8 years now and they have not been here in two years. It took dozens of calls and emails to get them to do anything.
So, now I want to figure this out and maintain it on my own. I didn't know enough about solar at the time to know this was a grid tied system.

That said, because it's a grid tied system, the inverters don't work unless they get grid power so even if they are connected to the solar panel, they would output anything right? Withe the breakers on, the inverters work but how can I test them since there is 120VAC on each leg from the grid?

To answer questions;

>I would start with an aggregate measurement first. An AC ammeter when the system is running would allow you to see what
>the output is. Better yet would be one that could convert to kWhs so you could get a daily output and compare that to an
>estimate from PV Watts.

That's the problem. With the breakers on, there is always 120VAC on each leg so no way to know if it's the grid or if it's the solar AC.
So, there is something missing in this for me so far.

>If I understand you, you want to test your micro inverters. Is the panels on the roof? If you can get a DC clamp on amp
>meter on the PV wire from the panel, you can see what amps are being pulled. What type of problems are you having?
>Do you have anything that monitors production ?

The panels are actually on a canopy which is on a very steep hill. That means that all of the panels other than the top of the hill are extremely hard to reach.
The problem is that because of the breakers needing to be on, I have no way to know what is going on. We are no longer getting any kind of savings since nothing seems to be reaching the power company. We've not seen a cut in our bill for almost two years.

I figured if I could test the system right up to the grid, then I would know if it's the system or something on the grid side that is no longer working. I don't understand the digital meter they have but will have to try to dig up a manual so I can see what's going on.

The manager is useless, it shows 607 watts being generated. When we first noticed the problem, we were getting around half our discount from the power company so I figured half the system was not working. It just took me a long time to get on this because it's a very time consuming job and I don't have much time.

>Most micro-GT inverters have a communication link system. Your Pantheon II, Integrated microinverter communicates with
>data over the AC lines from micro-inverters. If you don't have the comm head-end unit you should purchase one so you
>can monitor each panel performance.

Right, that would be the case had they not messed up the manager.

So, at this point, I just want to be able to test each panel and each inverter as a starting point. Or, at least enough of them to know that there is some usable output and if that's the case, then I'll contact the power company to have them look at their stuff on the house wall.

Or, maybe I should be calling them before doing anything else because maybe it's something on their own end, on the wall.

diWhy said:

That's the problem. With the breakers on, there is always 120VAC on each leg so no way to know if it's the grid or if it's the solar AC.
So, there is something missing in this for me so far.

Click to expand...

Power in Watts equals Amps times volts. You know the voltage will always be line voltage of 120 volts AC. If you can measure Amps with a Clamp as suggested by others you can see whether the Watts the Manager corresponds with the actual power flowing. It is only a starting point to confirm that the manager is reporting correctly.

Yes I read that and will go do it asap.
I called APS, the power company and they tell me this system should be putting out around 1200-1500 KW monthly on good months. According to them, it put out 21KW last month , 17KW this month etc. They show that it's been getting worse over time starting over two years ago.
I'm not sure the person I spoke with is correct because when the system was installed, the bill shows it was generating around 600KW month on a good month. Even that is strange since it's a 10.5KW system and when it was working well, I could see on the manager that it was generating over 8000KW/h regularly.

So, maybe something has not been right since day one.

Testing:
I have micro inverters, installed myself, and so some experience. If the inverter is making power, then DC amps can be measured on the PV line of each panel. DC amps will give you an indication of the power under good sunny conditions. When the sun is off, the AC current at the microinverter will be next to zero. When the microinverter is making power, the power is equal to the volts on the line times the amps measured on the AC line. Most microinverters are on some type of a trunk cable, so hard to get at the AC amps of any one unit. But of you have 8, 250w panels on one trunk, you should see amps close to 2000w under ideal conditions. If you can get at your connectors, you can disconnect the panel on X number of inverters (in the dark) and then measure for those left connected and repeat to try to isolate any weak or dead units/panels. Mine and I think most US microinverters are connected to 240v so their output can't cause out of balance on the backfeed to the utility transformer. Pantheon appears to be a 240v unit as well, so be sure of your line voltage when you calculate your watts, to not be confused.

I should have been more clear that the Amp measurement and calculation of Watts was only an instantaneous measurement. That is why I referred to it as a first step. The number that matters is kiloWatt hours each day (kWhs). That requires another device that can measure and log over time. I cannot make sense of your numbers because the units are unclear. Once you get that squared away then you should be able to tell how significant that decline is and move on to the next step of isolating that to a bad micro or two.
If APS is your power company they are only seeing the net production after your loads. Perhaps your loads have increased and consumed more of your power. There is a $100 device that I use to measure my loads and production and that might help. It is call Emporia Energy ,monitor and there are several other energy monitors including Sense. Emporia was the best price and gave me the data I wanted. It reads out in kWhs so you can relate that number to how your power company charges you.

Ampster said:

I should have been more clear that the Amp measurement and calculation of Watts was only an instantaneous measurement. That is why I referred to it as a first step. The number that matters is kiloWatt hours each day (kWhs). That requires another device that can measure and log over time. I cannot make sense of your numbers because the units are unclear. Once you get that squared away then you should be able to tell how significant that decline is and move on to the next step of isolating that to a bad micro or two.
If APS is your power company they are only seeing the net production after your loads. Perhaps your loads have increased and consumed more of your power. There is a $100 device that I use to measure my loads and production and that might help. It is call Emporia Energy ,monitor and there are several other energy monitors including Sense. Emporia was the best price and gave me the data I wanted. It reads out in kWhs so you can relate that number to how your power company charges you.

Click to expand...

I have 3 formal ways to monitor my production and to observed losses in my 250 foot power run, I put one of these meters at each end. Cheap and easy solution to see what was going on at the panel site without a phone app or anything else. I just removed the cover from my connection box, wire this meter in, and actually made a temp enclosure from an old butter tub and set in in a sheltered location under my panels. The total KWH needs to be reset after 999 but it is good for a quick look at what is going on.

I used one of those to measure the Amphours while parallel top balancing. Very good value

Yes, I have similar and I was thinking about mounting one on each of the four sections that are wired together.
What I call section 1 is 11 panels, section 2 is 10 panels, section 3 is 11 panels and section 4 is 10 panels.

I made a basic diagram of what I've got and was going to fill in the panel/inverter voltages.
However, I got stopped at not knowing how to test the output of the inverters, hence my question of course.

My overall consumption actually went down since I installed this. Initially, I was using almost 5000 watts of power 24/7 running a software development environment but over time moved most of that away and down to around 1000 watts now. I always had excess generation so was able to see that clearly on my bill.

>If you can measure Amps with a Clamp as suggested by others you can see whether the Watts the Manager corresponds
>with the actual power flowing. It is only a starting point to confirm that the manager is reporting correctly.

I'll be doing that as soon as I get the chance. The thing is that the power company and I can clearly see that the system is not generating what it should be. APS told me that the meter is unlikely to be at fault, that if it's working at all, it should be fully functional therefore it's the generation that has changed.

The manager is all messed up so I cannot count on it to tell me what is being generated so I can already rule that out.
However, I can clearly see on my electric bill how it's gone down and down and down over time to the point where it's now generating maybe 20kw/day.

>The number that matters is kiloWatt hours each day (kWhs). That requires another device that can measure and log over time.

Yes, I shared what I know so far without measuring, meaning, what the power company is showing me, above.

>I cannot make sense of your numbers because the units are unclear. Once you get that squared away then you should be
>able to tell how significant that decline is and move on to the next step of isolating that to a bad micro or two.

This is mainly my question, asking what I need to do in order to get to that point. I'm providing what I know but some of it doesn't make sense to me yet since this is all new to me. I've never had to deal with a device that must see grid power in order to run and so have no idea how one deciphers what it's putting out since it's connected to power to begin with.

I can get out there and measure the amps but what am I looking for? The grid is connected to the four segments, each with a 15 amp breaker.
What ever I measure amps or watts, aren't I just measuring the grid?

Sorry but this is where things aren't clear yet .

See image. If you have a clamp on amp meter or clamp on meter like I posted link to, put that on L1 or L2 (either of the 240v wires) at each breaker, or any place on that 240v line. If it is the panel meter that I suggested, connect the wires to the 240v, so the 240v is powering the meter. The put the inductive clamp around only one of the power wires. The meter will record KWH for that branch of your system. You can reset it daily. If you get 2 meters, you can monitor two branches the same day and compare output, which would be useful.

For example if branch 1 has 10 amps, it is making 10x240=2400 watts. Do that for 3 hours and you get 3x2400 kwh. The panel power meter will record the KWH and also let you see amps and watts in real time.

Does that help?

I can see you are confused about the system's function with the grid. I will describe something that might make more sense and then try to apply that to your install. Suppose you have a sub-panel to run 20, 500w lights on a large garage. The subpanel is fed by a main breaker. Inside the subpanel you have 4 breakers, each powering 5 of those 500w lights. These are 240v lights and pull a little over 2 amps each. So a circuit that had 5 of them, should be pulling a little over 10 amps if all of the lights are on. You walk into the utility room where the breakers are and put an amp meter on each of the black wires, on each of the 4 circuits. (Assume a black and a red wire come from each breaker) You get the following readings.
Breaker 1, 10.6 amps
Breaker 2, 10.5 amps
Breaker 3, 8.3 amps
Breaker 4, 6.1 amps

How many lights are not on?

The micro inverters when making power look no different than a load on a circuit, except rather than having a slight voltage drop at the load you have a slight voltage drop the other way. My panel site, 250 feet from the house is showing about 250v-251v when at my main breaker I am running 246v or so. I have 4, 30amp circuits at the panel site and each of them should be showing about 20 amps under ideal conditions.

Looks like you'd have 1 off on breaker 3 and 2 off on breaker 4.

I'm not so much confused as I am new to it and is why I'm asking for input and help so I can learn more about the aspects I don't know yet.
With everyone's help, it gets clearer all the time.

Today, I'm thinking I should call another solar company to come and assess what I have as a starting point since they should already know everything. From there, if it's a simple fix, I'll have them take care of it but if their assessment is a bunch of time consuming work but I know what needs to be done, I can tackle it on my own.

That actually might be a good starting point. There is only one place where I can get a clamp meter in but they didn't label the wires so I won't know which section I'm testing. The diagram I created above was by spending a few hours testing physical wires to the first panel mounted on the canopy where they just used twist ties to connect the wires so I was able take those off and test. That's how I at least know which sections are which now but from there, have not gotten back to test and was planning on it.

If the system is underperforming, it could be some inverters failed, and it could be panels degrading.
Biggest reason for people to see less power than they expect is that panels normally put out less power than "STC" rating from lab test conditions. But yours has decreased compared to originally?
Other big reason is intensity of light varies with weather and season, not obvious without measurement.

Clamp ammeter reading each inverter, if accessible, is a way to compare them without software/communication gizmo and see if some failed.

If the inverters are going bad, warranty is one option and replacing with different brand is another.
I think most models of Enphase microinverters are supposed to be pretty reliable.
I like string inverters rather than microinverters. All panels in one string need to be same orientation. Calculating maximum number of panels allowed in series is critical to avoid over-voltage destruction of inverter.
Used or new old stock string inverters can be had fairly cheap (sometimes $0.10/W e.g. $500 for 5kW), could be connected to existing array in place of microinverters.

If you turn off the breaker for all of the circuits but one, you should be able to identify (with a current clamp or inductive sniffer) which circuit is active. At the least, if you measure current at your four breakers, you can see if any are lower than the others. That might tell you that you have some inverters that are off.

Since the string sizes are fairly equal at either 10 or 11 panels I agree with the suggestion of @DThames to measure current (Amps) which might give you a way to rank each section to focus on the one with the least current. Presumably that might be the one which may have a failing micro or two. Then it is on to the testing of each micro. Do not dismiss the failure of a trunk cable or a section of cable.
I had an outage with my micros and it turned out it was the AC trunk cable. BTW someone mentioned to be careful disconnecting the leads unless the panel is dark. That is good practice with string inverters because you do not want to disconnect under load because the spark can damage the connector. However I am not sure this applies to the AC trunk cable or to micros because there is no load (current) on the DC connector until the micro goes through it's boot up process after being connected. Someone with more knowledge may want to comment.

At the time, the installer told me the panels (Mage) were no longer being manufactured and the company had filed for bankruptcy. The inverters were also no longer or hard to get until more would become available. When I started seeing the signs of the installer leaving me hanging, I started buying spare inverters so have a box of 20 or 30 of them.

The panels I can no longer find but I don't care. It's a large enough system and my usage has gone down that if I could get even half of it to work, I'd be happy. I doubt I have 21 inverters that have gone bad but as mentioned, the system is not even generating 1KW of power in good sun these days.

Yes, I am now aware of not pulling the connectors off the panels under load. Is it enough to cover the panel with a heavy blanket first or should I turn off the breaker for that section then test each panel?

First step was to I identify what's going on, get some information which I'll be able to do thanks to all your input, I'll have some idea of what I have to do next. It makes no sense to me that it's not generating anything considering its size and it seems relatively simple. Even with the manager dead, and even with some panels dead (I know of 1 dead one) and even with some of the inverters dead, I should be seeing something useful coming out of this big system but there is nothing to show on my billing which is why I have to dig.

Once I have it fixed or have a good idea of what is wrong, I can decide from there what I'll do.
The options I've thought about are...

I could replace the inverters and just go DC with an inverter/battery setup but then I lose any credits I get from APS.

I could keep it connected to the grid as it is or take half off the grid and the other half to my own inverter/battery setup.

I could simply add batteries to my UPS systems and use that to keep certain things running overnight, off the grid.

I've called several local solar companies and it's interesting how many are in fact out of business, number out of service. I've got one that says he'll call me back. If that call doesn't come in, in the next day or two, I'll go deeper on this. In the meantime, I'll try to get out there with a clamp meter tomorrow to get some basics and post what I find.