Solar panel VOC accuracy ?

Submitted: Wednesday, Mar 08, 2017 at 10:46
ThreadID: 134434 Views:2360 Replies:2 FollowUps:10
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Have just purchased a new panel and specs read 21.67 voc . I measured the voltage at the panel in full sun and 26º ambient and was only showing 19.1, should i have any concerns?
thanks
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Reply By: qldcamper - Wednesday, Mar 08, 2017 at 11:11

Wednesday, Mar 08, 2017 at 11:11
Yes it is worth a talk to whoever you got it off.

Was the panel pointing directly at the sun or laying flat?

Would also do a short circuit current test and see how much short that comes up.

A couple of volts doesn't sound like much but makes a big difference to the performance of the panel in low light conditions IE, getting a little output and not getting any.
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Follow Up By: Member - wicket - Wednesday, Mar 08, 2017 at 14:50

Wednesday, Mar 08, 2017 at 14:50
Thanks, now how do I perform a short circuit current test ?
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Follow Up By: qldcamper - Wednesday, Mar 08, 2017 at 15:06

Wednesday, Mar 08, 2017 at 15:06
Best to use a clamp type amp meter, if you dont have one use any amp meter rated at least 50% higher than the short circuit current in the specs of the panel.

I am also assuming you dont have a regulator on the panel....have you?

if not cover the panel to block all the light, connect the output leads of the panel to the probes on the multimeter securely as in with screw type connectors and set the meter up to read the highest current it can.

Get someone to uncover the panel and expose it to good sun, as soon as you get a good reading cover the panel again, no more than one to two seconds.

If your not confident get someone thats familiar with meters to assist you.
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Follow Up By: Member - wicket - Wednesday, Mar 08, 2017 at 16:53

Wednesday, Mar 08, 2017 at 16:53
Well my elcheapo multimeter is only rated to 10 amps but the panel is rated at 13.4amp , i do have a clamp meter that will handle the higher current but I'm not sure if i can use the plug in the probes ,only 2 plug (only com and one other )holes not 3 like multi one being amps. So if i plug in both cables and set the clamp meter to dc amps then using the probes will this work?
Thanks
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Follow Up By: qldcamper - Wednesday, Mar 08, 2017 at 17:32

Wednesday, Mar 08, 2017 at 17:32
if you use a dc clamp meter you wont need to use the probes, just securely connect the output leads from the panel and put the clamp around one cable.

Remember just briefly uncover the panel, just long enough to get a reading.

You dont have a reg in circuit do you?
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Follow Up By: Member - wicket - Wednesday, Mar 08, 2017 at 17:52

Wednesday, Mar 08, 2017 at 17:52
will give it a try but i thought for a clamp meter to measure amps there had to be an appliance drawing power
no reg just the leads
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Follow Up By: qldcamper - Wednesday, Mar 08, 2017 at 20:10

Wednesday, Mar 08, 2017 at 20:10
make sure it is a DC clamp meter.
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Reply By: Batt's - Wednesday, Mar 08, 2017 at 13:22

Wednesday, Mar 08, 2017 at 13:22
I'm no expert but after doing some research I would say no don't worry about it because there are a lot of things that have to be just right for it to reach it's peak output. Ranging from the temperature of the panel while 25 deg is considered good it may be a 25 deg day but your panel may be 30 deg plus to touch so it will lose approx 2.5 % efficiency for every 5 deg above 25 deg. The different months of the yr will also come into play and the area you live in as well. Also the sun has solar cycles which are constantly changing etc etc.

I checked my 170w panel one day recently and it was putting out around 15 - 17 v which surprised me but it was a very hot sunny day and it's sitting on top of an aluminium canopy with a small gap for airflow between the roof and panel. I should have measured the surface temp because it was probably 50 deg plus.

AnswerID: 609258

Follow Up By: qldcamper - Wednesday, Mar 08, 2017 at 13:34

Wednesday, Mar 08, 2017 at 13:34
I would be concerned if the open circuit spec can not be achieved on a sunny day.

The test your referring to, was it with the panel still hooked up? Nominal voltage and open circuit are completely different things.

Out of interest, what are the os and nom specs for that panel Batt?
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Follow Up By: Batt's - Wednesday, Mar 08, 2017 at 16:02

Wednesday, Mar 08, 2017 at 16:02
As I mentioned earlier I'm no expert but I would expect that you could put any brand of panel in the sun and not get a peak reading every time because the conditions have to be right I may be wrong.
My neighbour has a different brand of solar panel for his vehicle and his oc varies as well.


All I done was check the volts one day with a voltmeter stuck the pos/neg into the wire coming out of the panel before it goes into the redarc bcdc charger I have done this a couple of times before and got different readings I was using the latest one as an example.


22v OC and I don't have a clue what nom specs are or mean here's a link to the panel if you want to look it up http://stores.ebay.com.au/Bit-Deals/Solar-Panels-/_i.html?_fsub=12521457&_sid=302026428&_trksid=p4634.c0.m322
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Follow Up By: qldcamper - Wednesday, Mar 08, 2017 at 16:25

Wednesday, Mar 08, 2017 at 16:25
Fair enough, im not sure what you interpret oc to mean but i read it as open circuit, which is not the case if it is connected to a working charging system.

Open circuit is with no current flowing to load down the voltage reading, spec reading should be easily achieved.

All good.
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Follow Up By: Batt's - Wednesday, Mar 08, 2017 at 20:11

Wednesday, Mar 08, 2017 at 20:11
I thought it wouldn't make any difference to how much power was produced by the panel if it was tested before it goes into the regulator or if it is not connected and tested as an open circuit. So there is a difference you learn something every day.
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