Basic low cost ways to test (as a user level diy QC) individual solar panels? - Page 1
Forum section: electronics / general

author: evb149
author_rank: Regular Contributor
timestamp: April 28, 2022, 07:58:28 pm
content: Hi, I'm wondering what are some resources available for the testing as a user for diy QC of good / bad panels vs. their specifications? (0-22V / 0-6A / 100W).I just want to see if the panels I am getting are working correctly and meeting their general rough expected performance and are free of functional defects.Ultimately I'm planning to be using a very small low voltage DC system just to run equipment and charge low voltage DC battery backup reserve either 12 / 24 / 48V battery and 12-22V coming in from the 100W panel(s).I also want to obviously be able to use the power so if there are good reliable cheap basic equipment suggestions for a LV DC DC-DC MPPT controller / charger I guess I could get / use that as a rough indication maybe vs. test setup equipment.Basically I'd be looking for achieving / quantifying the approximate maximum power & {V, I} delivered under light conditions that are as maximal as possible within the next week or so. Testing could be a fully manual process with a standalone voltmeter / ammeter / luxmeter / resistive load or if there's some automated system for doing it that'd be fine too.I haven't gotten any DCDC converters / inverter / battery charger equipment as a load so I don't have any such thing to hook the panel under test to to see if it is producing NNN W power in that way. I wasn't thinking of buying such off the shelf but I guess if there's some good quality / really inexpensive & readily available MPPT DC-DC battery charger unit or something which also measures / reports power I could get / use that vs. improvising / acquiring test setup equipment?It seems like I'd potentially be able to use:* Calibrated lux sensor of some kind to measure the sunlight intensity at the panel during a test; (I don't recall what standard wavelength vs. sensitivity curve might be needed). Or maybe there's a "local" weather station or something in the area that would report "close enough" values given known latitude / longitude / time of day so the only variable would be local micro climate clouds / haze and ideally I'd test when "pretty clear". Suggestions for DIY or COTS inexpensive but useful units? I don't happen to have any just-freezing platinum cube handy for a SI blackbody source.* Fixed load resistance approximating the MPP full power load given the panel stated max. power V&I specifications, or better: Adjustable load resistance capable of dissipating or sinking variable amounts of power at 23V-0V 7A-0A (~100 W for a small panel). Load level could be possibly manually or automatically adjusted to achieve rough MPP maximum power point operation for a given moment.* DMM Ammeter for measuring current unless integrated into the tester apparatus.* DMM Volt meter for measuring the loaded and unloaded voltage unless integrated into the tester apparatus.* Measurement of time, longitude, latitude coordinates, and temperature sensor for approximate panel surface temperature during test.So obviously I can cobble these kinds of things together given time from individual parts, but I'm wondering what resources / parts sources / equipment could facilitate this testing?In particular I have no calibrated photometer / lux meter or optical source, though I have various photodiodes and small area test solar cells, LEDs, and such I could hook up if there's a means of rough calibration.Secondarily I don't know what good / cheap 12-24V / 100W rated load resistors are available as parts or whether some quick hack with incandescent bulbs, nichrome wire, heating elements, electrodes in a saline bucket, or whatever is the most viable quick and dirty solution for this. I'm guessing nichrome wire and a sliding jumper might be a easy manual option if nobody has made a variable power DC-DC SMPS power sink or something cheap.Ideas / suggestions?

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 29, 2022, 04:45:42 am
content: A 10mF capacitor and 0.1 ohm resistor in series will let you get an IV sweep using a scope (voltage across resistor is current, then use the second channel for voltage across the combination). Then use a load (e.g. resistor or incandescent light bulb) to discharge the cap in order to reset the setup for the next run.Quote from: evb149 on April 28, 2022, 07:58:28 pmA very cheap sensor would be to use a small solar panel connected to a multimeter measuring short circuit current. Just have it at the same angle as the panel under test.

author: Fflint
author_rank: Frequent Contributor
timestamp: June 25, 2022, 10:55:06 am
content: Like the other poster said get an IV curve on a scope then compare it with the datasheet. The important bit is near the "corner" (some people call it a knee). It is the part where the panel is most efficient.A good panel will have a curve that goes right then down with a very narrow turn radius. Same type of panel that has a very wide gradual turn has some deterioration.Also, when buying panels that are of the same type and if they were kept in the same place I would take a voltmeter with me and just check their open circuit voltage at same lighting conditions. Any panel with substantially lower voltage may be internally damaged.Finally, if you can wait till nighttime you can use your mobile phone camera to do a check. For this your mobile phone has to be able to "see" infrared. How to check this? Very simply. Take a TV remote in a dark room and open your camera app. Can you use the TV remote as a light source your mobile phone sees? If yes, you can use it to test your panels.Basically you need to supply voltage to the solar panel so some current flows through it. Make sure you use a current limited psu to avoid damage to pv panel. Then panels will emit IR light (same as a TV remote). By looking at how even the illumination looks you can find dodgy cells.

author: Towger
author_rank: Super Contributor
timestamp: July 24, 2022, 08:06:13 am
content: Another option is the the use of a thermal camera.This YouTuber goes through testing second hand panels and the types of damage often found.https://youtu.be/_HKW7mwPiMI

author: Psi
author_rank: Super Contributor
timestamp: July 24, 2022, 08:17:35 am
content: Quote from: Towger on July 24, 2022, 08:06:13 amThat is useful to know. Another use for the Flir E(4)8

author: Siwastaja
author_rank: Super Contributor
timestamp: July 24, 2022, 02:27:53 pm
content: Or just build any ghetto style adjustable resistance, wait for a sunny day, aim the panel directly to the sun, measure current & voltage with two multimeters, manually find MPP and compare to the datasheet values. Power is in the right ballpark, except if you are up north/south and it's winter time.