Measuring PV panel performance

[Hedges]

Zoomed in on the one bad panel. Good news it it can be tested in-situ, so no need to disconnect anything to inspect for failing panels. Works best during operation.



Those were Sharp 165W. Now for AstroPower 120W and SunPower 327W


Two panels as power source, producing 79 Voc, 41V @ 2A into panel under test

 

[Berseker]

Is this tool any good for testing panels??.

US $56.29 50%OFF | EL400B/ EY800W Photovoltaic Panel Multimeter Auto/ Manual MPPT Detection Solar Panel LCD MPPT Tester Voltage Testing Tool

56.29US $ 50% OFF|El400b/ Ey800w Photovoltaic Panel Multimeter Auto/ Manual Mppt Detection Solar Panel Lcd Mppt Tester Voltage Testing Tool - Multimeters - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

a.aliexpress.com

 

[RCinFLA]

A load tester that has a constant voltage mode, like DL24, can be used to test panel power output. Watch watts reading as CV load is raised. Power should peak at CV near Vmp of panel for given panel temp. If panel wattage is greater than load tester can tolerate you have to do it quickly before load tester overheats.

Feedback loop response time on load tester is slow and it may oscillate up and down a bit if you adjust CV loading too quickly. I have heard of some having trouble with oscillation. An electrolytic cap across tester input should help stabilize oscillation.

 

[Hedges]

Straight from the mouth of Will (same brand, different model.)

 

[fafrd]

The array being tested. Originally 9s2p installed around 2004 or 2005, now 12s2p with the column of 6 panels on the left acquired later.
These Sharp NE-Q5E2U panels are paralleled with 24s AstroPower AP120 into one Sunny Boy 5000US GT PV inverter. One one occasion, inverter reported 357 Vmp, Astropower delivered 3.71A Isc, Sharp (panels on left of array) delivered 3.20A Isc, Sharp (panels on right of array) delivered 2.17A Isc.

View attachment 63329

Tester, measuring Rload. Voltmeter (here set to ohms) is across MC cables for PV input.
Heavy-duty knife switch connects PV to power strip with oil-filled radiators as load.
General-duty knife switch shorts for Isc.

The heavy-duty switch is rated 600VDC 30A, so could be used to test a string of panels.
General-duty switch is not DC rated. It would probably work fine with single panel voltage & current, but I always open circuit with heavy-duty switch.
If I was testing series string, the general duty switch would still be adequate to hold off Voc or carry Isc, but couldn't be expected to interrupt current so heavy duty switch must be used.

A suitable series connection of several heaters could be used as load for this 2000W array, but their resistance would need to be same/similar so no one gets more than 120V applied. Their switches and thermostats are not suitable to interrupt DC, so thermostats are turned all the way up and switches are set without load using ohm meter.

View attachment 63331

Measuring Voc with heavy duty switch open, Isc with both switches closed, V(load) & I(load) with heavy duty switch closed, general duty switch open

View attachment 63333 View attachment 63334 View attachment 63335

So the Sharp panels you installed in 2004 showed this level of degradation 17 years later (2021).

Were you successful in getting Sharp to recognize a warranty claim?

My SinEdison 335W panels were installed in 2016 but unfortunately I may be experiencing degradation similar to what you saw in your Sharp panels, but much sooner.

And since SunEdison went through bankruptcy in 2018, I’m afraid I’ll be left holding the bag no matter what level of degradation I discover.

So my primary interest is in characterizing the relative performance of my 12 panels as well daily and cost-effectively as possible.

Seems like a quick way to determine severe degradation is to use an IR camera as you have done, so I’ll look over the product you’ve linked to and will consider getting one as a first step (since that allows some characterization without the need to disassemble the array).

But since I’m guessing I will eventually need to characterize electrical degradation, I’d appreciate any recommendations from your experience.

I was originally attracted to these $50 testers but Will’s video has convinced me they are not worth it.

So the kind of quick and easy testing I am considering would involve testing two panels side-by-side to determine relative performance and since I have an spare SCC and a 24V battery,I’m thinking just setting up two panels to charge the battery at midday and measuring current from each into the SCC might be the easiest thing to do. Equal current translate so equal performance so I can determine the best panel pretty quickly and then characterize the performance of all 11 other panels relative to that on a relative basis pretty easily.

An even easier test I could perform would involve connecting a single panels to a spare pair of hot water heater elements I have connected in parallel, monitor current through an ammeter.

Vmp is ~35V and the parallel connection of both elements will translate to about 3.5 ohms, so I should end up at around Vmp based on original specs and will end up at at whatever voltage below than than results in current close to Imp if performance has degraded…

Beyond that, any severely-underperforming panels should be checked for hotspots using an IR camera before putting them back in service.

When I read through your posts and this thread, I feel like I am seeing my future. So any advice as to how you’d approach a 12-panel array starting to deliver severely degraded output would be greatly appreciated…

 

[Hedges]

I couldn't get through to Sharp when I tried back the, haven't tried in quite a while.
Only a percentage of panels showed severe degradation. All one array, one environment, but some are biased more positive/negative than others (spent 1 year on a transformerless inverter.) Because I didn't check string current before, don't know if degradation was due to that brief period and PID.

Will may have said it seemed not so accurate, but what's 10% between friends? Good for comparison, anyway.
Either that tester or resistive load like I did should work. Keep toggling back to one reference panel, to correct for changes in sun.

The only degradation mechanism I understand how to partially reverse and to prevent is PID. (well, some others may also depend on magnitude of voltage.)

Now that we know, try to buy quality with track record. And I'm trying to use transformer-type inverters which can be grounded as desired. (My TriPower can't.)

 

[Ampster]

So any advice as to how you’d approach a 12-panel array starting to deliver severely degraded output would be greatly appreciated…

I thought your controller readings were fairly close from year to year? Are you still getting 5000 kWhj per year? Why do you think it could be panel degradation? I forget if you get panel level statistics from your micro controller or what size your system is.?

 

[efficientPV]

I would put more faith in that $50 tester than Will's method of depending on a charge controller to get the right spot. Getting the power point is very simple technology that can't be faked. All you need is two fairly accurate A/D conversions. I do it with a scope.

 

[conquistador]

All you need is two fairly accurate A/D conversions. I do it with a scope.

Could you explain how you go through the load that quickly? In your picture, you seem to take 30ms?