Folding Solar Panels - check the wiring

Submitted: Saturday, Dec 02, 2017 at 13:00
ThreadID: 135936 Views:3811 Replies:4 FollowUps:4
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Hi all

I thought this worth posting FYI to all those with folding (or multiple) solar panels. Maybe this has already been "discovered" and posted but regardless here it is.

I discovered a recently purchased a 12V 200W folding panel (2 panels) wired incorrectly - working, but not right. They do not have blocking diodes in series with each output. Others on this forum will know whether it is just reduced efficiency, or potential damage to one of the panels, that can result from unequal panel outputs in parallel like this - especially if one in shade and one in full sun.

When I opened the connection panels, they have Bypass Diodes across the output of each panel (as you would use in say a 24V series connection), but the outputs are connected directly in parallel as a 12V system.

So unless I am on the wrong track as per any documentation I have seen regarding solar panel connections for parallel and series connected arrays, I have re-wired mine (soldering iron required) to put a blocking diode in series with each panel.


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Reply By: RMD - Saturday, Dec 02, 2017 at 14:25

Saturday, Dec 02, 2017 at 14:25
Is the way they were supplier/wired actually wrong? If wrking it would seem they are correct and the diode is there to protect the panel if someone reverses the connection to the battery. As I understand what you have posted, the way it was originally will have no negative effect on normal operation.
Two panels can be in parallel and supply twice the amps of just one panel.

If you have fitted diodes in series with the panel, then you have reduced the overall voltage of the panels putput voltage by 0.6V and the diode has to carry ALL the panels current output and not overheat and fry itself.
Must be a big diode, is is cooled.

The whole idea is to have the maximum of the panel energy get to the battery I thought. Perhaps I have that concept wrong.
AnswerID: 615327

Follow Up By: 808 - Saturday, Dec 02, 2017 at 15:27

Saturday, Dec 02, 2017 at 15:27

You may well be right and in practice it may not matter much depending on what device the solar panels are connected to. And I will not profess to be expert in solar panel theory, nor have I done any tests to check all the possibilities.

The Diode only has to be large enough to carry the maximum continuous current of the one panel it is being supplied from, and the loss of 0.6V would be irrelevant in most situations.

Having an electronics engineering background, let's say it is "technically wrong" (even though it does work) if you look at any information relating to connection of solar panel arrays - a search for "diodes on solar panels" will provide many links and images to the theory. However, with the blocking diodes in circuit, my logic also tells me that an MPPT controller would be vital to getting the most out of each panel such that both panels are supplying current.

I appreciate there are many varying scenarios for the use of solar panels (directly connected to batteries or on various controllers or regulators) and in most cases it may not matter. But the theory as I see it is generally not to allow batteries or other solar panels to push reverse current through panels that are not generating enough output for whatever reason as that is wasted energy.
FollowupID: 886249

Follow Up By: Dean K3 - Saturday, Dec 02, 2017 at 16:37

Saturday, Dec 02, 2017 at 16:37
I would be more concerned about solar panel discharging start battery if it was left attached without a diode to prevent back flow, than the solar panel supplying too much or being partially shaded

I had this occur using a 80w fold out from a australian electronics component supplier, took awhile to figure out what was going on.

Battery fully charged by middle of day left attached early evening looked at led battery status one step away from deep discharge -managed to start engine (just) following morning.

with few days of testing I figured out was due to lack of blocking diodes, contacted manufacturer of solar panel/regulator for their input -sure enough we don't fit them.

ended up replacing with a GSL MPPT unit and on advice of the manufacturer installed a blocking diode inline between regulator and power leads -so far no more issues.
FollowupID: 886252

Follow Up By: RMD - Saturday, Dec 02, 2017 at 17:43

Saturday, Dec 02, 2017 at 17:43
An MPPT controller can't reverse switch to allow any current to flow back into the solar panel. That is like saying a laptop supply will supply the computer battery to the 240v grid.
FollowupID: 886255

Follow Up By: Member - Phil G (SA) - Wednesday, Dec 06, 2017 at 20:37

Wednesday, Dec 06, 2017 at 20:37
I have installed the extra diodes on mine - thet are 15A Schottky diodes so forward voltage drop is only 0.3V which is irrelevant to the solar panel voltage.
FollowupID: 886378

Reply By: the_fitzroys - Sunday, Dec 03, 2017 at 09:30

Sunday, Dec 03, 2017 at 09:30
Why not just take it back to the retailer if it was recently purchased? They'd either provide a new one or confirm with the manufacturer that it was correct. More time to sit back and enjoy life!
AnswerID: 615342

Reply By: Frank P (NSW) - Sunday, Dec 03, 2017 at 11:55

Sunday, Dec 03, 2017 at 11:55
I believe you are correct in doing that, Ken. I have done it to all my paralleled panels. It stops wasteful backfeed from lit panels being dispersed as heat in shaded panels.

It has nothing to do with stopping back feed from the battery to the panels - the regulator does that.

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AnswerID: 615347

Reply By: TerraFirma - Monday, Dec 04, 2017 at 14:59

Monday, Dec 04, 2017 at 14:59
I'm re-wiring any of the cheapies to work via Anderson plug to a Redarc Regulator. With the no name stuff the panels can be ok but the rest is crap. I also use a Redarc Solar Monitor to see how many volts and amps I'm getting to the battery etc.
AnswerID: 615362

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