Solar panel tester.

[Mattb4]

Looking up possible solar panel testers I see a few that are available from China that are all basically the same meter with different names. The two versions are up to 400 watt (in led or panel display) and up to 800 watts. Does anyone have any personal experience with these? It could prove to be a handy thing if it works.

 

[Hedges]

Will did a report on one of them.
I think he felt their measured power wasn't real close to what he thought the panels delivered to an SCC, but they did work.

I used DMM, switches, and electric heaters to test Voc, Isc, and some intermediate voltage/current.
Some of my bad panels did show up with Voc/Isc, but some looked OK there, only tested bad under load (poor Vmp/Imp.)

 

[Mattb4]

Thanks I just searched and watched Will's video on it. From what I garnered it was not so much that the results were inaccurate as it was the cost of the meter and the need for a consumer to test their panels made it something not worth while.

I guess in my thinking is that it could possible help in trouble shooting. At that point $50-65 is not a bad price.

ETA: After almost pulling the trigger on ordering one I decide Will's advice does apply. I can always test my own setup using heaters, voltmeters and DC clamp on. Plus even if my SCC is not pulling all that my panels could produce I am unlikely to run out and buy a new one.

 

[Hedges]

Measuring PV panel performance

I suppose I could buy a solar panel tester like Will reviewed, but that doesn't feel DIY enough to me. Besides, I'm a cheapskate, and I try to do things in the most difficult (and expensive if the equipment wasn't on hand) way. I'm presently working on an underperforming string of Sharp 165W...

diysolarforum.com

 

[fafrd]

My 4kW grid-tied array installed in 2016 is showing some severe performance degradation and I think I’m going to have to do some testing to understand whether only a few panels are degrading faster than the others or they are all degrading at a similar rate.

Testing against STC is obviously impossible but I’m thinking that at a minimum I can compare two side-by-side panels to identify my best panel and compare all of the others against that in terms of % of bear to determine how much extra degradation I’m looking at.

Ideally, I’d live to be able to generate a full I-V curve for two separate side by side panels if there are any low-cost testers that provide that capability.

So I’m curious as to how anyone who has done so has characterized panel performance and whether these MPPT testers make the job quick and easy.

Whether it’s using one of these MPPT testers or not, I’m also interested in any cheap and easy ways to generate crude I-V curves (at least two points on either side of Vmp as well as measuring Voc and Isc).

Any advice on how to most easily and effectively characterize relative panel performance appreciated…

[EDIT: Just followed the link provided by Hedges and am digesting that thread now…

What a fantastic forum this is ]

 

[Ampster]

Any advice on how to most easily and effectively characterize relative panel performance appreciated

In your case the other variable is the micro inverters. A simple short circuit or resistance load with switches like Hedges suggested would be the quickest way to get a high level ranking of panel performance. Then test each micro with your best performing panel to test each micro. How practical that is may depend on your roof?
The least expensive and easiest way without going on the roof would be a simple Watthour meter on your Solar leads on the wire(s) from your roof and compare that daily production to what your micro controller is reporting during the same solar day. I bought a simple Coulomb Counter on Amazon for less than $40. I think it was DC but a quick search would also reveal ones that work on 240 Volt AC.

 

[RCinFLA]

Consider the amount of power they must dissipate. They usually only load panel for a short period of time, every so often, to keep their internal heating down. They can abruptly jump around in their reading when clouds impact the illumination level. With short duty cycle of loading it makes it much more challenging for them to hit optimum MPP point.

Some measure unload Voc voltage and just figure Vmp will be 0.83 x Voc along with 0.95 x Isc current for I_mp current.,

 

[Ampster]

Any advice on how to most easily and effectively characterize relative panel performance appreciated

As you shared with me on a separate thread the issue seemed to be inconsistent readings from your micro controller reports of generation and your clamp on Amp meter. Which is why I suggested the hypothesis to test the accuracy of your micro controller readings.

As @RCinFLA duggested it is more difficult to eliminate insolation differences when testing individual panels, especially over the time it would take to do them all on a roof installation.

Comparing Watthours over the same day reported by two devices might be worthwhile to test whether your controller is reporting correctly.. For example I have Enphase micros and and an Emporia Energy monitor. During different times of the day their cumulative KWhs can vary by as much as one kWh. However at the end of the day yesterday one reported 35.4 kWhs and the other 35.7 KWhs. That is an difference of less than one percent and all I could expect from an inexpensive device like the Emporia.
Here is one inexpensive device:
DROK AC Multimeter, AC 40-300V 100A 110V/220V Voltage Current Power Factor Frequency Electric Energy Monitor with Current Transformer, Digital LCD HD Display, Volt Amp Watt Detector Reader Panel https://a.co/d/aaecx8o

 

[Rednecktek]

So having 2 of the 800w testers due to flakey internet access, here's my $0.02

1: They only go up to 60VoC which makes them pretty useless for anything larger than a milk crate or boondocking rig.
2: They're slow to respond finding the max power point, but they do get there.
3: They do work well for comparing parallel VS series connections so you can verify the panels are talking correctly and not fighting each other (**COUGHHARBORFREIGHTCOUGH**) which is handy.
4: They come with both alligator clip probes AND MC4 probes which makes getting it to talk to your panels pretty easy, unless you're using one of the 800 flavors of barrel connector.

 

[Hedges]

Clamp ammeter around PV wire would give current.
If you plug in "Y" cables, you can read voltage and current, at whatever operating point the microinverter has it at.
If one diode-bypassed section is bad and delivering half the current, or zero volts, that may jump out at you.
If you can open junction box and probe you might see different voltages across each diode.

The IR camera would not be quantitative, but would highlight which panels are suspicious and should be measured.

 

[fafrd]

In your case the other variable is the micro inverters.

Yes, I’m going to sort out with my Microinverter supplier first that the Microinverters are performing correctly.

This post / thread was anticipating that even after that issue has been addressed, there’s a reasonably-high probability I may have some or all of my 6-year-old 12 335W panels that have degraded more than they should have…

A simple short circuit or resistance load with switches like Hedges suggested would be the quickest way to get a high level ranking of panel performance.

Short circuit allows you to measure Isc, but typical degradation results in a ‘slumping / rounding’ of the I-V elbow around Vmp and Imp, and a short won’t help to characterize that.

I think I can rig up something using my two spare electric water heater elements.

Then test each micro with your best performing panel to test each micro. How practical that is may depend on your roof?

I’m not going to waste any time checking my MicroInverters unless instructed to do so by the supplier. They seem responsive so if they are treating this issue as a warranty claim, I’m going to proceed as they instruct.

The Microinverters are reporting much more power production than I’ measuring (as in close to 200%), so either the Microinverters are faulty and the panels are fine, or the Microinverters are fine except for reporting / gateway monitor but the panels have degraded.

If the supplier replaces all the Microinverters I will do that first - testing anything on the roof will not be easy - step one is to get to the point that reported array production matches what I measure getting into the mains panel (which ties to what Tyler utility meter reports).

The least expensive and easiest way without going on the roof would be a simple Watthour meter on your Solar leads on the wire(s) from your roof and compare that daily production to what your micro controller is reporting during the same solar day. I bought a simple Coulomb Counter on Amazon for less than $40. I think it was DC but a quick search would also reveal ones that work on 240 Volt AC.

Thanks for the suggestion but for now, the Microinverter supplier seems to be accepting the discrepancy between my annual clamp-meter current measurements at the end of the home run and the production report coming from their gateway monitor.

Power generated should equal 240V x measured current, and at the moment, reported power generation is almost 200% x 240V x measured current…

Once they get me to the point that reported power generation ties to measured power generating, I’ll finally be able to get an easy bead on how my 6-year old panels are performing.

If it turns out they’ve degraded severely after only 6 years, I’ll need to characterize how many and how badly before determining whether any defective panels remain safe enough to be put back into the array.

I’m happy I did a DIY install with components I selected myself, but managing failures and warranty issues like this is the hidden cost of that decision…

 

[fafrd]

Consider the amount of power they must dissipate. They usually only load panel for a short period of time, every so often, to keep their internal heating down. They can abruptly jump around in their reading when clouds impact the illumination level. With short duty cycle of loading it makes it much more challenging for them to hit optimum MPP point.

Some measure unload Voc voltage and just figure Vmp will be 0.83 x Voc along with 0.95 x Isc current for I_mp current.,

Is Voc an accurate reflector of panel health?

I thought I read somewhere that typical panel degradation is characterized by smoothing / slumping of the elbow at Pmsx / Vmp rather that changes in Voc…

 

[fafrd]

As you shared with me on a separate thread the issue seemed to be inconsistent readings from your micro controller reports of generation and your clamp on Amp meter. Which is why I suggested the hypothesis to test the accuracy of your micro controller readings.

Not sure which ‘Microcontroller’ you are referring to - the Gateway associated with my Microinverters (which reports instantaneous and daily production)?

I’ve already confirmed that is not accurate and the vendor has agreed.

The getaway is reporting production which is almost 200% of that reported by my utility meter and confirmed by my clamp meter measurements. I’ve only discovered this huge inaccuracy 6 years after the system was out into service. For year one and year two I checked monitor versus utility meter versus monthly electrical bill and they all tied, but since then I’ve trusted the gateway and gotten lazy…

As @RCinFLA duggested it is more difficult to eliminate insolation differences when testing individual panels, especially over the time it would take to do them all on a roof installation.

I’d only test panels after the Microinverter issues have been resolved and only after disinstalling the entire array from the roof…

Comparing Watthours over the same day reported by two devices might be worthwhile to test whether your controller is reporting correctly.. For example I have Enphase micros and and an Emporia Energy monitor. During different times of the day their cumulative KWhs can vary by as much as one kWh. However at the end of the day yesterday one reported 35.4 kWhs and the other 35.7 KWhs. That is an difference of less than one percent and all I could expect from an inexpensive device like the Emporia.

I’ve already convinced my Microinverter supplier that instantaneous power generation is a bit over 50% of what their gateway is reporting and they they have agreed that means there is a problem with the equipment which they have agreed to address.

I’m assuming that means that sometime over the next month or two I’ll get back to a position that reported power generation ties much more closely to what the utility meter is reporting (and I’m confirming with my clamp meter).

I’m only going to dive into checking out individual panels if that future accurate view indicates that my production has degraded by much more than the 7% my panels specifications warranty guaranteed after 6 years…

Here is one inexpensive device:
DROK AC Multimeter, AC 40-300V 100A 110V/220V Voltage Current Power Factor Frequency Electric Energy Monitor with Current Transformer, Digital LCD HD Display, Volt Amp Watt Detector Reader Panel https://a.co/d/aaecx8o

Thanks for the link. My biggest regret as a first-time DIY installer is that I trusted the gateway after validating it in years one and two and didn’t have the foresight to install a 3rd party energy monitor before trusting it blindly for the next 4 years.

Whether it’s a unit like this or a more comprehensive energy meter such as that offered by Emporia, I’m certainly going to get something into place (though that appears to not be on the critical path to get the reporting issue with my Microinverters addressed…).

 

[fafrd]

So having 2 of the 800w testers due to flakey internet access, here's my $0.02

1: They only go up to 60VoC which makes them pretty useless for anything larger than a milk crate or boondocking rig.
2: They're slow to respond finding the max power point, but they do get there.
3: They do work well for comparing parallel VS series connections so you can verify the panels are talking correctly and not fighting each other (**COUGHHARBORFREIGHTCOUGH**) which is handy.
4: They come with both alligator clip probes AND MC4 probes which makes getting it to talk to your panels pretty easy, unless you're using one of the 800 flavors of barrel connector.

I’m not sure I understand the implication of your coughing fit, but appreciate your insight.

Sounds like one of those little testers might be worthwhile for testing a single 335W panel (69V limit means 2S string is too high).

But the simplest thing for me to do will be to use what I already have - a resistive load and a multimeter…

 

[fafrd]

Clamp ammeter around PV wire would give current.

My multimeter only shows AC current through the clamp - are you saying the AC current setting will also report DC current or that the DC current setting also works though the clamp?

If one diode-bypassed section is bad and delivering half the current, or zero volts, that may jump out at you.
If you can open junction box and probe you might see different voltages across each diode.

Yeah, once the panels are off the roof, checking Voc and checking voltage under resistive load seem like the easiest things to scan for gross failure / defect.

The IR camera would not be quantitative, but would highlight which panels are suspicious and should be measured.

The pictures you posted made an impression on me - what was the magnitude of investment you made to capture pics like that?

The IR camera seems like the easiest way to check fir gross depredation installed on the roof (hot spots).

 

[Rednecktek]

I’m not sure I understand the implication of your coughing fit, but appreciate your insight.

The newer Harbor Freight mono panels have been documented to work well in series but don't play well in parallel for some odd reason... or allergies

Sounds like one of those little testers might be worthwhile for testing a single 335W panel (69V limit means 2S string is too high).

The tester errors out over 60v so if your panels do 69 it won't even work for a single panel.

But the simplest thing for me to do will be to use what I already have - a resistive load and a multimeter…

If you can do the job with what you have, it's cheaper than buying special equipment.

My multimeter only shows AC current through the clamp - are you saying the AC current setting will also report DC current or that the DC current setting also works though the clamp?

Nope, meters to amp-clamp a DC line are built to do it. An AC clamp won't detect squat.

 

[fafrd]

The newer Harbor Freight mono panels have been documented to work well in series but don't play well in parallel for some odd reason... or allergies

Got it - thanks. Never had an array with panels in series but sounds very strange that identical-spec panels could have any issue. Just one more thing to watch out for, I suppose…

The tester errors out over 60v so if your panels do 69 it won't even work for a single panel.

No, single panel Vmp is ~35V, so I can test a 1S1P or 1S2P string, but 2S1P would be out of reach…

If you can do the job with what you have, it's cheaper than buying special equipment.

Absolutely, as long as there is not too much screwing-around involved. Have a tester with MC4 leads is actually one of the most attractive features of those pre-built testers. I’ll need to rig something up to connect fo the MC4 connectors on my panels…

Nope, meters to amp-clamp a DC line are built to do it. An AC clamp won't detect squat.

Was afraid of that. My cheapo multimeter only reads AC current through the clamp, so I’ll need to break the MC4 connection to read DC current inline or invest in a more expensive multimeter…

 

[Ampster]

The getaway is reporting production which is almost 200% of that reported by my utility meter and confirmed by my clamp meter measurements. I’ve only discovered this huge inaccuracy 6 years after the system was out into service.

Remember the PG&E meter is Net. The unknown variable is consumption. Unless you have reliable data about consumption I would be skeptical about reaching a conclusion that is not supported by verifiable facts. What do the statistics about production of each inverter tell you? Do they add up to the totals that the Gateway is reporting. Does the Gateway report instantaneous data or does in only report 15 minute chunks of data like my Enphase system does. If it is instantaneous a better correlation or error correction could more easily be compared to the instantaneous reading of you clamp meter.

 

[Hedges]

Is Voc an accurate reflector of panel health?

I thought I read somewhere that typical panel degradation is characterized by smoothing / slumping of the elbow at Pmsx / Vmp rather that changes in Voc…

No. Sometimes it shows if panel is bad, but can't say it is good with certainty.

If you study the measurements I took, some of the 5 bad panels had Voc or Isc out of line. But a couple, those measurements were good. Only V(load) and I(load) showed they were bad. I'm guessing one diode-bypassed section put out low current. Full voltage, full current from the other sections pushing past it. But resistive load showed it bad.

My multimeter only shows AC current through the clamp - are you saying the AC current setting will also report DC current or that the DC current setting also works though the clamp?

As was just answered, No.
I bought the Harbor Freight Ames 1000A AC/DC clamp meter for this. It has 0.01A resolution, which many others do not.

DC with this resolution and low range is done with Hall Effect sensor. For some reason I don't understand those are a bit expensive; they are just a piece of doped silicon, and op-amp, and a coil (more accurate to cancel field under test than to use voltage from Hall sensor directly.)
There are magnetic ammeters good for starter current.

AC is usually current transformer (core clamped around wire). I also have a Fluke probe which is Rogowski coil - helical spring is flexible wrap-around probe, and with no core it has 20 kHz bandwidth.

The pictures you posted made an impression on me - what was the magnitude of investment you made to capture pics like that?

That camera was about $600. I borrowed it.
Same brand has $120 cameras to plug into a phone, but much lower resolution.

People say there are many cheap cameras with the same poor dynamic range sensor, and that Flir for a high price is worth it. I think the one I borrowed was good too.

The IR camera seems like the easiest way to check fir gross depredation installed on the roof (hot spots).

Yup, in-situ, operating.

 

[Ampster]

Never had an array with panels in series but sounds very strange that identical-spec panels could have any issue. Just one more thing to watch out for, I suppose…

Your NEP micros are connected to two panels, correct? Do you know if they are in series or in parallel? Does the gateway give you any information about voltage or current? That might be a clue about panel degradation if you can believe the numbers.