Testing PV Power Output

4 Posts
Apr 27, 2010 02:02 pm
Testing PV Power Output

I watched the "Solar Panel Testing" video on the AltE website and measured my panels. The open circuit voltage (voc) = 18.28 volts. The short circuit current (isc) = 4.35 amps. The rated voc = 22.1 volts and the rated isc = 5 amps. Can I use the measured numbers to determine the performance of my panels? They're warrantied by the manufacturer at 90% for 12 years.

578 Posts
Apr 27, 2010 02:12 pm
Re: Testing PV Power Output

for your own knowledge, sure, you could see what the modules are doing.  to get useful information, you will also need to know the irradiance, as well as temperature in degrees celcius. 

i would bet there is nothing wrong, but send more data on exactly how you tested.

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"Making Renewable Do-able"

Tel: 877.878.4060 x107  or +1.978.562.5858 x107
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4 Posts
Apr 27, 2010 02:23 pm
Re: Testing PV Power Output

Thanks James,

I measured them exactly the way you did it in the video. I'd guess the temp was ~18 C. By "irradiance" do you mean was the panel in direct sunlight? Yes, as best I could get it. It was about 1:00 PM at 37 degrees Lat with the panel lowered from 90 degrees to get the highest reading.
4 Posts
Apr 27, 2010 02:51 pm
Re: Testing PV Power Output

Sorry, I should have added the panels are 85 watt BP mono crystalline and they're nine years old.

From the label:
Vmp = 18 V
Imp = 4.72 A
Voc = 22.1 V
Isc = 5 A

578 Posts
Apr 27, 2010 04:35 pm
Re: Testing PV Power Output

irradiance is measured with a tool called a pyranometer.  essentially irradiance is the rate of sunlight power hitting a given spot at any instant in time.

here is a link to one. 


the 85 watts number is measured at what is called STC.  without going too far, standard test conditions (STC) is done assuming 1000w/m^2, 1.5 air mass, and 25 C cell temp. 

irradiance is directly related to current output, so the numbers you measured, even if only characterized by "sunny" conditions, would suggest your module is fine being that you were at 87% (4.35/5) of its current rating without any further technical data at hand.

the voc number was slightly low, but could be easily explained if the module was warm.

for more info regarding pv technology

this is a good book,


and you could also take classes if you think you could stand 16-40 hours of me in person Wink


hope that helps

altE staff

"Making Renewable Do-able"

Tel: 877.878.4060 x107  or +1.978.562.5858 x107
Fax: 877.242.6718  or +1.978.562.5854
May 2, 2010 05:48 am
Re: Testing PV Power Output

Here is some information I found to be useful, Jimmie O as a "tool" to make comparison with.
Another good "tool" I have found to be useful is my Bogart TriMetric 2020 monitor.
Other good tools are, angle finder, 12"x2"x4" cut square on on least one end, a good flat board roughly 3'x3/4"x6" and, a magnetic compass, which of course you'll want to know the degree of declination from solar south. It helps as well to secure the angle finder to one end of the broadside of the flat board.
Being knowledgable of our Sun helps as well. Knowing which days are the shortest (winter solstice) and the longest (summer solstice) and which days have an equal number of hours with the night (vernal and autumnal equinox.)

Just for fun;
The analemma of Mars.
Saturns north pole.
Have any of you every thought about what its like to be on a boat, on the open water, looking out ahead of you in the direction of travel, seeing nothing but open waters? Its tempting to let the boat go on its own feeling safe that it will not hit anything like a log floating just below the surface or, as unbelievable as it sounds, an iceberg.
Our entire solar system is like that boat and there is nobody at the helm, there is no helm. We are traveling through space without a clue as to what is out in front of us. People on Earth thousands of years ago new of this simple fact and they set to watching the stars trying to gain knowledge of what was to come.
We still do this today only, most likely, we will pick up a newspaper and turn to, our horoscope.
« Last Edit: May 2, 2010 05:50 am by Thomas Allen Schmidt »

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