Don't wanna have to clamber up on the roof but ???? - Page 1
Forum section: electronics / general

author: fourtytwo42
author_rank: Super Contributor
timestamp: June 03, 2020, 06:02:55 pm
content: Debugging advice!I have a 1Kw array on the roof made of four 60 cell 260W panels in series.Recently the peak power available has dropped from around 1100W to 750W, so I cleaned them as this is usually the reason for a drop in peak power, however that didn't fix the problem, just raised the peak to around 850W (yup the were dirty) , so in desperation I got out the DVM!ISC was still a very healthy 9.3A (spec 9.1A) but VOC had dropped from the specified 150V to around 136V.More interestingly the MPPT controller was running them around Vmpp 108V instead of the normal (and specified) 120V.These things are inaccessible big time being on the roof but I suspect a panel fault as a faulty controller would not affect VOC (IMOP).I am thinking along the lines of a shadow diode gone short circuit, there being 3 strings of 20 cells in each panel so 12 strings in all and one diode short on the array would reduce the output voltage by 1/12th.I don't think its a corroded tabbing wire (1st thought) as I couldn't see any substantial corrosion through binoculars and my guess is such a fault would affect ISC.Does anyone here have any experience of array faults, do my symptoms sound familiar?

author: ahbushnell
author_rank: Frequent Contributor
timestamp: June 03, 2020, 07:02:57 pm
content: Corrision was the first thing that come to mind. I don't want to go on the roof either.Good luck.

author: Gregg
author_rank: Super Contributor
timestamp: June 03, 2020, 07:36:25 pm
content: A corroded connection would be easier to locate with a thermal imaging device. Even if the connection is inside a junction box, the whole box should be a lot warmer than the surroundings. If you don’t already have one, this would be the perfect excuse to own one.

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 04, 2020, 03:01:16 am
content: With a magnetic field probe, you'll be able to tell the difference between a shorted diode (will still have current through that part of the string) and an open in the string (no current). Particularly for the second case, probably a good time to use the warranty if there is one.

author: fourtytwo42
author_rank: Super Contributor
timestamp: June 04, 2020, 08:59:51 am
content: Quote from: ahbushnell on June 03, 2020, 07:02:57 pmThanks, two of them have been up there 4 years and the other two 3 years, wish I had hung them so the junction box was at the bottom

author: fourtytwo42
author_rank: Super Contributor
timestamp: June 04, 2020, 09:03:03 am
content: Quote from: Gregg on June 03, 2020, 07:36:25 pmI tried an IR thermometer from a distance hoping to detect a change in cell temperature but either any difference was overridden by the heat from the sun and/or the shorted string is generating the same current as the rest! Tried pinging the junction box area but again nothing detectable, probably just to far away......10 Metres/30 FtSWMBO already thinks my hobbies are excessively expensive so sadly an IR camera is out of reach for me

author: fourtytwo42
author_rank: Super Contributor
timestamp: June 04, 2020, 09:11:28 am
content: Quote from: NiHaoMike on June 04, 2020, 03:01:16 amA very good idea although I think I would have to be in close proximity for that (on the roof), I had tried to measure cell temperature as a way of finding an open string but either I was to far away (10M/30Ft with an IR device) or the sun's radiation swamped any detectable difference) or indeed the diode is shorted so all the cell currents are the same.I tried the warranty angle (5 years) but they want the panel serial number and guess what I failed to do before installing them

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 05, 2020, 02:12:35 am
content: Quote from: fourtytwo42 on June 04, 2020, 09:11:28 amIf the gap between the panels and roof allows, use a camera on a selfie stick to record a video of the labels under the panels.

author: fourtytwo42
author_rank: Super Contributor
timestamp: June 27, 2020, 08:19:11 am
content: Well I finally put the tower up and retrieved one panel from the end of the array, the system being flexible still works at reduce power on the remaining three.I took the cover of the junction box but it is filled with white gooo so no inspection possible beyond confirming no serious overheating. I did however make some comparative measurements of this standalone and the remaining three panels (in a string)Model AC-265P/156-60S, Vmpp 30.98, Voc 38.16 (-0.3%/C), Isc 9.2A all @25CBarcode Voc Vmpp mV reverse @1Amp Visible damage2615113205572 33.3 1030 NoneRemaining 3 100.8 82.2 3274The reverse voltage test is intended to show up shorts in shadow diodes and appears to show none.Voc is considerably below spec in all cases, Vmpp for the remaining three is also low as it was for the four, so if there is a faulty panel it probably remains in the three still on the roof.I have a feeling that final debug will not be possible till all the panels are back on the roof with there junction boxes pointing down so they can be reconfigured to isolate one at a time and compare Vmpp as determined be the controller, unless some damage is encountered when turning them.Accesing each panel means taking the tower down, moving the base and rebuilding itI think that's what passes for exercise during lockdown

author: Kleinstein
author_rank: Super Contributor
timestamp: June 27, 2020, 11:07:52 am
content: What type of cells are these ? With thin film cells it is kind of normal that the voltage will drop ober time when they age and some aging is normal with these cells.The specs are usually for some 25 C and full sun, this is a combination one would hardly get in real life except for a very cold day in may. It only takes some 30 K temperature rise to get 10% less power.

author: fourtytwo42
author_rank: Super Contributor
timestamp: June 28, 2020, 12:00:24 pm
content: They are polysilicon panels. The system is instrumented and this fault suddenly started appearing earlier this year, as I think I said elsewhere it seems to only happen on very hot days when the peak recorded power is around 20% less than normal, Vmpp is also lower than normal.Whilst removing panels today I saw a snail trail on another panel and managed to get a picture, this is invisible from the ground due to the angle. In the scheme of things this will be the last panel to be removed.Having taken the measurements I have so far I think the probable way to id the faulty panel will be by running the system using different sets of three (missing out one) for several days at a time and record the results (once I have them all rotated with the connectors at the bottom for accessibility).

author: Seekonk
author_rank: Super Contributor
timestamp: June 28, 2020, 01:14:14 pm
content: Probably worthwhile building tap connectors and running three wires down to monitor each panel. I had a lightning event and it caused several bypass diodes to short. It appears to have saved the panels as they worked with new diodes installed. But everything does not show up right away with lightning. I have multi strings in parallel and have yet to fully test each string. Not a fan of isolation diodes, but might be installing them this year so I so a shorting panel doesn't bring everything down.

author: fourtytwo42
author_rank: Super Contributor
timestamp: June 29, 2020, 01:42:45 pm
content: A very good idea Seekonksort of along the lines of a battery BMS giving monitoring of each panel.Damm wind this morning putting up a panel caught me at the critical moment panel near vertical in my hands whilst standing up swaying on the top of the tower, thought I was about to become a hang glider for the 1st time in my life lolsAnyway gotten another serial number and some more snail trails, one more panel to get down to record the lot.No burn marks in junction boxes found yet.

author: ahbushnell
author_rank: Frequent Contributor
timestamp: July 02, 2020, 01:52:15 pm
content: Quote from: fourtytwo42 on June 29, 2020, 01:42:45 pmThat snail trail looks like a problem.

author: fourtytwo42
author_rank: Super Contributor
timestamp: July 02, 2020, 08:17:20 pm
content: Quote from: ahbushnell on July 02, 2020, 01:52:15 pmI agree they don't look pretty, some small semicircular burn marks on the edges of some cells too (same two panels as snail trails) both purchased 2 years ago, these have all grown as were not there originally.I have yet to run the serial numbers past the manufacturers as I have as yet no electrical proof of performance degradation, partly because they were the last two to be turned over to make the connectors accessible and partly because the weather has closed down (showers & overcast) and I am fairly certain bad things only happen in hot sun (clear sky all day).Interestingly the other panels that are a year older have no snail trails or semi-circular burn marks on the edges.

author: ahbushnell
author_rank: Frequent Contributor
timestamp: July 04, 2020, 08:56:13 pm
content: Quote from: fourtytwo42 on July 02, 2020, 08:17:20 pmI have a panel that died and I left it outside leaning against the house. Latter I looked on the back and there were a bunch of black tracks.