Solar Panel Output??
Submitted: Tuesday, Mar 30, 2004 at 08:28
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Member - Nobby
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.
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: 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 - 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