Solar Panel IV Curve Tester Recommendations  - Page 1
Forum section: electronics / general

author: AJ3G
author_rank: Regular Contributor
timestamp: July 10, 2021, 10:41:47 pm
content: All:This topic is a bit new to me. I need to measure and graph hundreds of solar panel IV curves. As I have done some research it appears there are a couple of test instruments that do just this, but I wanted to see if I could solicit some real world feedback from those who have used them before making a selection. This is an area of Test and Measurement I have virtually no experience in, and what I have kluged together thus far, is too cumbersome to not only setup but use considering the quantity of panels I must characterize.Thus far I have viewed the Seaward and HT Instrument offerings. Looking for some real world feedback, and recommendations.ThanksRich

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 10, 2021, 11:23:41 pm
content: Easy way to make one is to have an electronic load in "constant voltage" mode and sweep it while monitoring current. It would also be useful to have a small solar panel beside the one you're testing and monitor the short circuit current of that panel as a measure of the light level.

author: AJ3G
author_rank: Regular Contributor
timestamp: July 10, 2021, 11:26:00 pm
content: That is basically what I am doing now. I am then exporting the data for plotting in excel. Unfortunately, it takes too much time when attempting to do hundreds in a year.

author: Someone
author_rank: Super Contributor
timestamp: July 11, 2021, 12:35:29 am
content: SMU is the fully automated instrument for this:https://download.tek.com/document/Photovoltaic%202450%202460%20AppNote%20(3).pdfThe Keithely units are more programmable and able to do things like presenting a single numeric result in manufacturing, alongside collecting/logging/displaying the full data. You can quickly get the forward and reverse characteristics, other competitors are Keysight, Yokogawa or Rohde & Schwarz. R&S have some cheaper options that are only 2 quadrant such as the NGL200, just as fast as the SMUs but not advertised as one.If you don't need reverse characteristics or high speed or integration in a single box, then a programmable DC load connected to a computer has been the usual solution for solar cell IV sweeps.

author: AJ3G
author_rank: Regular Contributor
timestamp: July 11, 2021, 12:48:47 am
content: That is great information. I will take a look at the SMU. I did some searches for application notes, but this one did not avail itself to me.The panels we are working with are all well below 100W. We have to characterize them after construction and deliver reports. I am using a DC Load at the moment, but each test is taking around 30 minutes to complete, and we need to go much faster.Rich

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 11, 2021, 01:01:33 am
content: Does the load support PC control? It would be easy to write a Python script to automate it, one point per second would be very reasonable.

author: floobydust
author_rank: Super Contributor
timestamp: July 11, 2021, 02:07:12 am
content: What is your light source, and what distance away? I found it varied with temperature and mains voltage, it does move around.Manufacturing personnel had trouble positioning the panel properly, had to make a tight jig to get consistent results. If the light source is close, then even 1/4"makes a difference.Ultimately the panel temperature goes up under test so you can't get high accuracy data.We just used a few switched-in power resistors to get about 7 data points, Isc, Voc, and 5 others and it was good enough.

author: AJ3G
author_rank: Regular Contributor
timestamp: July 11, 2021, 03:27:18 pm
content: The load I am using does not have Serial or GPIB interface. This is why I thought an all inclusive instrument for this application would be appropriate.The light source is approximately six inches away. We also have a test panel to compare to.

author: DougSpindler
author_rank: Super Contributor
timestamp: July 18, 2021, 01:32:09 pm
content: Take a look at the Mooshimeter.https://www.amazon.com/Mooshim-DMM-BLE-2x01A-Mooshimeter-Wireless-Multimeter/dp/B011W4L7JA/ref=asc_df_B011W4L7JA/?tag=hyprod-20&linkCode=df0&hvadid=242041198988&hvpos=&hvnetw=g&hvrand=4382281054637073765&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9032015&hvtargid=pla-570044788491&psc=1

author: floobydust
author_rank: Super Contributor
timestamp: July 18, 2021, 06:52:11 pm
content: We still don't know what kind of light bulb is being used. I've seen 300W incandescent halogen and also sodium lamps used. It's easy to be comparing spectral response by accident.Everybody has a different idea of making "sunlight".Is the Mooshimeter still active?Sparkfunretired it, and it's been many years since.

author: trobbins
author_rank: Frequent Contributor
timestamp: July 18, 2021, 11:33:44 pm
content: Rich, are you saying these are new panels? As in they have been made up from cells on a backing and then encapsulated by you? Are you doing other testing as well on the finished panels like insulation resistance and continuity? It sounds like you are making up your own pass criteria, based perhaps on STC performance of cells? Were the cells tested prior to assembling? Are the panels being used or sold based on a certain performance specification?

author: DougSpindler
author_rank: Super Contributor
timestamp: July 19, 2021, 12:15:26 am
content: Quote from: floobydust on July 18, 2021, 06:52:11 pmI think it is, they are still being sold on Amazon.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 19, 2021, 02:35:31 am
content: Quote from: AJ3G on July 11, 2021, 03:27:18 pmDoes it have analog I/O? Best solution might be to interface it to a microcontroller.

author: Berni
author_rank: Super Contributor
timestamp: July 19, 2021, 05:43:12 am
content: As others have suggested a SMU is the correct tool for this, they are the test instrument of choice for most kinds of static semiconductor testing. A lot of modern SMUs have built in graphing capability, older ones usually don't.However you might find that a SMU capable of handling 100W can be rather expensive. So unless you plan to also use it for other things it might not be worth it. But since solar panels are always used in the regime of them producing power you can get away with just an electronic load.Just find a electronic load with some sort of automation connectivity, RS232 USB GPIB LAN..etc. This is a good example for the use of instrument automation. The instrument is capable of doing the measurement at one data point, then you just use a PC with a script to run the instrument trough all the points and plot a graph. This can graph points as fast as the instrument can measure them. If this is something that is done regularly the same automation script can also generate a PDF report of the test, store the report somewhere, print it out etc. The report part is something standalone instruments don't do, but can sometimes take longer to make manually than even the measurement takes. Also since the script sets up the instrument for the test, it means that you eliminate operator errors, as it can easily happen that he puts in a wrong setting.This PC automation part does require some programing skill tho since there are not much in the way of ready to go software tools while its dificult for a ready to go software tool to be flexible enough to cover all possible test setups with like >5 instruments working together.

author: AJ3G
author_rank: Regular Contributor
timestamp: July 19, 2021, 03:28:51 pm
content: All:I am sorry for the late response to all this information. While i had subscribed to this thread, those messages alerting me to new post were sent to my junk mail box.These are panels which we purchase from another vendor and than integrate onto a PCB panel for space applications (space cubes, nano sat’s etc). We have a sample test article which has been tested. We are making a pass/fail criterion based on deviation from the test article. I have been able to obtain an Electronic Load with serial interface, and write basic script to plot the results.With the above in mind, this setup is not ideal for the quantity of panels that must be tested. At some point I need to document the test and set up a jig so that someone else can run the test on all these panels. We are getting a demo SMU, and HT Instruments curve tracer. I hope to resume this task in the next two weeks, and conclude what will be the most intuitive and time saving approach. If we can get away with the HT Instruments then that would be the first choice from a cost perspective. I had not been in the market for a SMU in the past, and was a bit shocked by the cost. Of course, we gladly pay more than that for other instruments needed to conduct other work.Rich

author: trobbins
author_rank: Frequent Contributor
timestamp: July 19, 2021, 11:42:28 pm
content: Rich, I hope you can manage to use such a commercial IV curve measurement instrument, although now you need to prepare a suitable controlled illumination system with temperature control, which may not be easy. As this is for pass-fail, the source spectrum does not necessarily need to align with the cells response and could I guess be even LED based. One preferred method is to use a small encapsulated reference cell and use its output to control the light intensity of the source during testing, and another small reference cell to plot the spatial variation over the plane of the panels during initial setup. A large LED light source panel may be appropriate, as it should be able to be part of a simple closed loop intensity controlled system, and achieve a short duration test period where temperature change is minimised due to illumination (depending on the test sweep period of the IV curve instrument). At one time, such PV panel test systems were based on the very short illumination period of a pulse discharge bulb to achieve one-sun illumination.

author: AJ3G
author_rank: Regular Contributor
timestamp: July 20, 2021, 01:27:21 am
content: Hi trobbins:This is very good information. I have reviewed some literature on the topic. In the case of the HT Instruments it is being shipped with two accessories, which I think help automate this process. The first is a reference cell for irradiation measurements. The second is a remote irradiation, temperature and tilt angle sensor.Both of these, from the available literature seem to be highly integrated with the instrument, so they will not provide much use with the SMU should that be the direction we chose. In that case, I think a little more work will be necessary to accomplish the same task.As I have stated in a previous post, I never had the opportunity to try and measure these parameters before. I am learning a lot about it, and it all seems very interesting. I have used normal TEK Curve Tracers for characterization of components, and despite having this experience never really looked into the SMU’s, or fully appreciated their capabilities.Rich

author: trobbins
author_rank: Frequent Contributor
timestamp: July 20, 2021, 03:51:20 am
content: At least you have a broad range of products to look at nowadays, although the vast majority are likely aimed at installation verification or maintenance processes for farms (with strings now pushing past 1kVdc).Absolute simplest pass/fail could be just Voc and Isc, and perhaps a loaded point in the vicinity of Mpp, if you had a room or box etc with a relatively even light source like a light table for inspecting xray films. If the panels are at the same temp, and the test duration is short (ie. a 3-way switch with 2 DMMs for current and voltage), then repeatability may be reasonable - which you could test by say doing 10 panel samples and then retesting the batch of 10 again a few times - but yes that would be manual entry in to eg. Excel.I presume the panels would be tested again once installed in end product.Does the panel OEM provide test certification of any kind?

author: AJ3G
author_rank: Regular Contributor
timestamp: July 20, 2021, 07:28:47 pm
content: Hi trobbins:The panels would be tested again on the end product. The goal at the moment would be to characterize them here, and save the plots with a serial number. This way we can compare quickly if something has happened while in shipment or during integration onto the satellite. Your idea of a light table seems very doable for me. I have room for something like this.The OEM provides a IV Curve plot of there own, but I am not sure I would call this an official test certification. From the looks of it, the document they produced is nothing more something to give us a “warm fuzzy feeling” that their panels are meeting advertised spec. Our whole system is tested after integration to TRL 4 (space qualified).Rich

author: floobydust
author_rank: Super Contributor
timestamp: July 20, 2021, 08:02:14 pm
content: The failures I observed were all bad interconnects between cells, and cracked cells was also common. How that shows up on the IV curve is pretty straight forward.I did not do a hi-pot test to confirm insulation/no shorts to the aluminum frame.