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Solar Panel Fun - Is it dead or is it alive...


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So one for the electrickery boffins out there.

My boat has two x 100W Polycrystal solar panels fitted side by side on the flybridge. (Specs are below)

It has a 30Amp PWM charge controller.

 

If i connect one panel i get 5amps charging, if i disconnect that panel and plug in the second panel i get no current charging... So one assumes the panel is dead

 

This is where it gets funky...

If i test the Open Circuit voltage (Voc) i get 21.8v on both panels. 

If i test the Short Circuit Current (Isc) i get 5.89A .

 

So it seems as if the panel is performing to spec but when connected to the charge controller on its own it doesnt seem to put any current to the controller.
The controller is fine as the other panel works when connected exactly the same... (note the panels are side by side, same sunlight and even the same wiring to the controller when i swap them so no differences there.

 

Any ideas? - Is it normal for them to die yet show both correct Voc and Isc? 

 

 

Panel specs:

Maximum Power:100W (Pmax) 
Maximum Power Voltage: 18 V (Vm) 
Maximum Power Current:5.55 A (Im) 
Open Circuit Voltage:22.5V (Voc) 
Short Circuit Current:5.99A (Isc) 
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Thanks team - it was the same cable - I literally disconnected at the actual solar panel and moved it to the second panel. So i can rule out cable between panel and controller.

 

Will measure Voltage at same time as doing Isc (Current Short Circuit).

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Yeah, the panel is stuffed. Be interesting to know the voltage when its providing the 5.89 a with the short. Probably below useful batt voltage.

If volts is ok, cabling problem.

It's short circuit current is 5.89 amps. How is that stuffed !? Thank watts. There has to be an intermittent fault or bad connection in the plug. If both panels are operating to spec, I am thinking the connector is dodgy. Giving it some more thought. The pins on the connector are not making contact properly thats why it tests OK when unplugged but one or both pins won't be connected.
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Well Island Time you were right - its dead...

 

I put a load on the panel (lightbulb drawing 1amp) and it lit the light but the voltage dropped to 9 volts straight away.
on the other panel if i did the same the voltage stayed around 17 volts.

 

So panel dead, now to find a new one the same size so its fits in same place! 

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For the above questions. Watts. Yep, watts are unknown unless you know both amps AND voltage. Hence my question above. The real answer to a panel is it's wattage, or P (power). P=amps x volts

if the panel cannot sustain sufficient wattage (P) to provide useful amps at a voltage that can be used to charge a battery( > about 13.8v) it is effectively useless. 

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So thinking some more- the voltage drops to 9 volts, which is basically half the Open Circuit Voltage (VoC).

So now im wondering if its a blown diode kicking out half the cells? Anyone know any way to test that if i cant find a panel the same size to test

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Cheers KM - i have two identical panels, and one is working mint so got a pretty good test bed.

I hate throwing stuff away that i cant explain how they are broken! So curiousity will probably have me buy a new one for the boat, then play with this one at home to learn some more.

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I had a panel that had been underwater and the copper ribbon behind the connector had turned to green dust. I dug it out with a knife to get to intact ribbon and soldered 2 new wires on then sealed with silicone. Working fine. Seems they are pretty hard to kill.

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Haha they were in the sun - hence one of them works one doesnt.

 

@CrazyHorse - not really in that when you measure the Open Circuit voltage the current isnt at 5amps. Likewise when you measure the short circuit current the voltage drops a little. you cant measure the two together and get that.

 

@StrayCat - Panels are probably 5 years old but they were bought by previous owner of boat so not sure where from etc. there is diodes in the connector box on the back of the panel itself.

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often the cells have a good warranty, but the panel itself does not. Worth reading the fine print on any new panel.

The diodes can of course fail on a panel like that. If they can be accessed  they can be tested and replaced if required, but on many panels this is impossible - destroys the panel.

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Sounds like a diode or a join in a string of the cells has gone, 9v at Short isn't bad for a 100w panel but it is a touch low. For example here is a different 100w panels volts/amps curve:

 

HmHaokV.png

 

Can you get us a picture of the black box on the panel with it's lid off if it comes off? Under the glass on the panel can you see any black/soot like marks between cells?

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You can't measure current open circuit, only potential (voltage). If the panel is delivering 5.8amps as in the specs when under full load (short circuit) then there is nothing wrong with it. There should be a voltage drop under load of about 5v. One thing I have come across is electrolysis. The cells are all linked and mostly using aluminium foil which then enters a junction box and using ss screws connect to the copper cables supplying the power. Over time the tabs turn to aluminium oxide unless salt is sealed out. The best sealant I've used is a silicon grease, stays liquid so doesn't dry out. Anyhow, good luck.

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