Solar Panel Output??

Submitted: Tuesday, Mar 30, 2004 at 08:28
ThreadID: 11672 Views:2278 Replies:11 FollowUps:5
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Can anyone give the true reading of their Solar Panels? I have two 80W and the best I can get is about 7.5amp. I spoke to the Solar Shop(who wired them up for me) and was told this is normal as the manafacturers always overstate their actual output on their specifications.My panel are directly in the sun,facing North etc.
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Reply By: Boeing - Tuesday, Mar 30, 2004 at 10:19

Tuesday, Mar 30, 2004 at 10:19
Hello Nobby, I would have thought that that was about right . 7.5 over say 6 or 7 hours of daylight gives 45 or 52 amps which is not bad.

Regards

Mark
AnswerID: 52532

Reply By: ianmc - Tuesday, Mar 30, 2004 at 11:04

Tuesday, Mar 30, 2004 at 11:04
Nobby, do you get only 7.5 from BOTH panels wired in parallel?
Amps = watts over volts, in your case 80/12= 6.5 approx X 2 = 13 amps.
Result depends upon strength of sun & angle and length(resistance) in wires
to where you measured the amps & maybe the accuracy of the ampmeter.
My 60w (5amp) solarex has NEVER got near to 5 amps. 4 has been about the best & often much lower.
If there is a shadow over even the smallest corner of it the output drops dramatically.
I understand that later models/types dont do this.
AnswerID: 52535

Reply By: Jon - '88 TD42 GQ - Tuesday, Mar 30, 2004 at 11:07

Tuesday, Mar 30, 2004 at 11:07
What voltage does it supply?

Power = Voltage * Current

So if it is providing 12V:
12 * 7.5 = 90W

So if you do get 12V from it I'd be hppy.
AnswerID: 52536

Follow Up By: Jon - '88 TD42 GQ - Tuesday, Mar 30, 2004 at 11:08

Tuesday, Mar 30, 2004 at 11:08
Oops.... TWO panels.... In that case, yeah not terrific, but probably alright since 80W will be the optimum performance.

Cheers.
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Reply By: Member - Nobby - Tuesday, Mar 30, 2004 at 11:19

Tuesday, Mar 30, 2004 at 11:19
It just puzzles me that you do all the sums and you should get 9.5amp ( which is in the specification sheet), but in reality I am only getting 7.6 max.(As per my multimetre) As stated have them in full sun, facing north, heavy duty cable etc, etc. I realise that I'm still getting enough to run my set up but why do they say you get "X" and you actually get "X" - something(in my case 2amp)??
AnswerID: 52538

Reply By: Member - Wim (Bris) - Tuesday, Mar 30, 2004 at 12:15

Tuesday, Mar 30, 2004 at 12:15
Nobby

Kyocera info KC80.
Max V = 16.9
Max A = 4.73
watts = 79.937.
This max performance. I have 2 x KC80. Very difficult to get max output. Still good setup though.

Hope this helps.

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AnswerID: 52543

Follow Up By: Member - Nobby - Tuesday, Mar 30, 2004 at 16:17

Tuesday, Mar 30, 2004 at 16:17
Wim that is what they say on mine to , so we should get 2 X 4.73= 9.4, but in reality I'm getting 7.5. Mind you I am still getting enough power to charge my two batteries.
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Reply By: Ray (Geelong) - Tuesday, Mar 30, 2004 at 12:44

Tuesday, Mar 30, 2004 at 12:44
Solar panels are rated to an industry standard in a controlled enviroment. They are subject to a brief flash of light of some makeup at I think 25c. What this boils down to is that in the real world you don't get what they say....great!
I have a 55 watt BP on the garden shed keeping a number of batteries alive. I get nearly 3 amps tops, usually 2.5
AnswerID: 52549

Reply By: Rod - Tuesday, Mar 30, 2004 at 12:56

Tuesday, Mar 30, 2004 at 12:56
Nobby

Three possible explainations given to me were:

1). Solar panel output is affected by the cell operating temperature. Panels are rated at a nominal temperature of 25 degrees Celcius. The output of a solar panel can be expected to vary by 2.5% for every 5 degrees variation in temperature. As the temperature increases, the output decreases. I've proven this by throwing a bucket of cold water over the panels on a hot day and seen the current climb.

2). Panels are typically rated at around 16V. I've been told that if we could run everything off them at 16V rather than 12V, they would operate more efficiently. Dunno how true this is ?

3). Is your load taking all of the current ? If you are charging a battery and that battery is fully charged, you may not see the full current.

Food for thought anyway. I use and efficiency of 75% of the stated output when doing my calculations.

Regards
AnswerID: 52551

Reply By: Member -Bob & Lex (Sydney) - Tuesday, Mar 30, 2004 at 17:48

Tuesday, Mar 30, 2004 at 17:48
If it does what you want who cares. All these things are done @ optimum conditions & we don't get that in the bush do we?
AnswerID: 52576

Reply By: Member - Jeffrey - Tuesday, Mar 30, 2004 at 18:12

Tuesday, Mar 30, 2004 at 18:12
Hi Nobby,
I have heard if you inprove their reflective amount ie,shinny foil,gal tin sheet it actually improves output by reflecting more light onto the panels..also the higher they are mounted the better,Hope this helps.
All The Best In Health And Wealth
Jeffrey (AKA JD)
AnswerID: 52580

Follow Up By: Moose - Wednesday, Mar 31, 2004 at 13:31

Wednesday, Mar 31, 2004 at 13:31
Excuse my ignorance - what has height got to do with it?
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FollowupID: 314497

Follow Up By: Member - Jeffrey - Wednesday, Mar 31, 2004 at 14:03

Wednesday, Mar 31, 2004 at 14:03
Hi Moose,
I cant go into all the detials or egzactly where i read it but i have been reserching photovoltics for some time now and I remember reading folks that live in elevated places produce more power,..I live in blacktown leeding up to foothills of the bluemountains which produces X amount of power but if I lived in lets say kurrajong it would be more eficient..more power I suppose put smiply,and not trying to put anybody down you are closer to the source ie the sun for those of you who dont know where kurrajong is it the begining of the mountains on the bells line of roads.
Hope this helps Moose and yes it is confuseing
All The Best In Health And Wealth
Jeffrey (AKA JD)
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FollowupID: 314499

Follow Up By: Moose - Wednesday, Mar 31, 2004 at 14:10

Wednesday, Mar 31, 2004 at 14:10
G'day Jeffrey
Thanks for that. I wonder whether it has something to do with higher elevations being cooler. As I understand it the cells lose efficiency as they get hotter. Which is pretty bloody useless really - one would expect that something that works off the sun would work better as it heats up. But I guess it's the light that does the work, not the heat.
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FollowupID: 314500

Reply By: Member - Rohan K - Tuesday, Mar 30, 2004 at 19:31

Tuesday, Mar 30, 2004 at 19:31
Gidday Nobby. It's that 20% inefficieny I spoke about over on OL, as explained to me by a solar panel techo. The manufacturer's specs are based on a certain (cool) panel temp in high intensity sunlight with full current load ignoring all current losses through wiring, heat losses etc.

You can discount these optimum specs by at least 20% for the real world.

Glad to hear however, that the two panels are delivering sufficient for your needs.
AnswerID: 52589

Reply By: phil - Wednesday, Mar 31, 2004 at 17:25

Wednesday, Mar 31, 2004 at 17:25
Have a look at this for a really good explanation of the proper use of solar panels. It coveres the matching of panels to loads, including batteries, and explains "where the power goes"

http://www.windsun.com/ChargeControls/PPT.htm

AnswerID: 52675

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