Solar panel

[keninpalamos]

I have 2 100w panels that seemed to have stopped working. With them disconnected and taking separate readings from each one I’m getting 10.46v. The regulator, a Votronic 250 MPPT is telling me it’s on standby as if it were dark. At the regulator solar panel input I’m getting a reading of 10.44v I’m guessing both panels are US. I’m in brilliant sunlight.

[Ocsid]

On the face of it it certainly looks that way, but two failing together in itself ring something of a warning that all might not be as it seems.

If "normal" 12 VDc charging panels we would expect an open circuit voltage to be around 20 VDC.

 

If selected for that controller, for use in parallel as opposed to series, they could be twice that. Though typically here, using two panels, the higher voltage is achieved with a series wiring of conventional 12 V DC use panels.

 

Any reason to mistrust the meter?

[keninpalamos]

The meter is ok and not a cheap one. I have used it at work and checked it against another meter only a few weeks ago. I fitted and wired in the panels six years ago (in Parallel) with the correct cables and connectors and have the Votronic control panel connected as well plus the starter battery connected on trickle charge from the regulator. It does seem odd that with everything disconnected each panel is reading the same and not connected to each other (10.46v). Readings from the starter battery are 12.5v at present and the leisure battery 12.3-4v. I only really need the batteries for tonight. I will go and look for a blue hook up plug as I’m on a site but don’t usually need to hook up but do have a lead with Uk plug. I’m in Bilbao by the way. Anyway that should get me out for the c#$p. Thanks for your reply. PS if I remember correctly the panels should be reading about 21-25v readings taken directly of the panels.

[colin]

It does sound odd that both are giving an identical low reading, are you 100% sure you haven't missed something connecting them both together still?

[Keithl]

Are the solar panels clean or could they both be equally dirty?

[keninpalamos]

Not clean but in brilliant Spanish sunshine. I was getting a better reading in dull wet England of 13.4

[keninpalamos]

I took the reading from each individual panel fly leads direct off each of the panels. The + and - are about 12 inches long. The end of each lead are marked + & - there are four leads. I can see each pair of leads quite plainly. The ends are not connected to anything as I have unplugged the solar plugs. All there is are 2 pairs of leads about 12 inches long so not a chance of anything else being connected or earthing out as the panels are on a fibre glass roof and the cables come through two separate weather proof unions on the roof which are made of plastic.

[Ocsid]

I still am bugged by two failing, they failing but still showing a potential 10 odd volts, and both closely the same potential.

These things all stacked together so neatly are exceedingly rare occurrences, making me really wonder what is being missed.

 

Keith raises an important point re being clean, more importantly is there any debris, dead leaves etc stuck on them?

 

Such things can cause a massive drop in performance, way out of proportion to the obstructed area involved.

 

This still leaves questions of why both are developing about neatly half the potential they ought?

There might be some logic to this laying in the interconnecting of the physical cell groups on the panel, which manifests in the potential being halved if one section of the panel is "blinded" by something like dirt, leaf etc.

 

I certainly would not jump to dumping these panels without a better understanding of the real issue they have. I don't buy the similarity of the "failures", I am sure we are missing something else.

[Keithl]

On the subject of being clean, are they in full sun or even partially shaded?

 

Like Ocsid I am struggling to comprehend them both failing so similarly!

[mikefitz]

Most solar panels in the 100 watt range have the cells arranged in two 'banks' connected in series, with a bypass diode across each 'bank'. If the series connection within the panel fails or one of the diodes were fail as a short, then you would see half the panels nominal voltage, which is the case, ( nominal panel volts open circuit is 21 volts).

 

Having exactly the same voltage on both panels is odd, one would expect a small variation.

 

It seems the panels have failed, if the panels are the flexible type this is expected, as they rarely have a long service life.

 

You may have limited success connecting the panels in series to deliver 20 volts or so to the controller. However if the panels are the flexible type, then overheating ( that causes failure in the first place), may cause damage to adjacent surfaces. Thus best leaving disconnected until they are replaced.

 

Mike

 

[mikejkay]

I had an identical situation with two flexible 150w panels failing abruptly and at the same time. I also went through the rigmarole of testing each panel with a good quality DMM. Both were down to about 10v so I didn't waste any grey cells and just replaced them. I should say that the panels were replaced under warranty as these particular panels had a bad track record for premature failure.

[keninpalamos]

Thanks for your input everyone. I'm now in Mojacar, Almeria where I live for part of the year. As you know we get very long sunny or full sun days here and I'm still getting the same readings on each panel. Although the panels have gone dull in appearance due to age (about 6 years) they are clean as they are easily accessible as the van is a poptop Autosleeper. I'm going to disconnect them at the regulator. and on my return to the UK will replace them. The van is parked in my garage here most of the time so they would not be doing a lot anyway. Again thanks for your views, advice and help.