Solar PV Module characteristics

[squelch]

Hi Guys,

do you know what is/are the implications if their is a mismatch of Nameplate Isc and the actual Isc from string that you will be testing. say, Module Isc : 9.08A and by site testing you only get around 3A ?

TIA

 

[Gavin A]

all depends on the sunlight levels. If in full sun perpendicular to the panel then you've got a problem, but that's unlikely to be the case in november.

 

[SibertSolar]

Module nameplate values are based on STC (standard test conditions) which are typically 1000W/m2 irradiance, 25degreeC cell temperature and air mass of 1.5. In order to determine whether your measured Isc in reality is in line with the manufacturer's declarations you need to measure the environmental conditions at the same time as measuring your short-circuit current. You can then extrapolate. (Something like the Seaward PV150 solartest kit + S200R multi-meter does this automatically for you). Most people will live with measuring just the irradiance, but temperature does make a difference too. Air mass is rarely bothered with as the coefficients are almost negligible.

 

[SolarCity]

I gave up testing with the temperature. Could never get my figures to line up with what they were supposed to be.

 

[squelch]

Module nameplate values are based on STC (standard test conditions) which are typically 1000W/m2 irradiance, 25degreeC cell temperature and air mass of 1.5. In order to determine whether your measured Isc in reality is in line with the manufacturer's declarations you need to measure the environmental conditions at the same time as measuring your short-circuit current. You can then extrapolate. (Something like the Seaward PV150 solartest kit + S200R multi-meter does this automatically for you). Most people will live with measuring just the irradiance, but temperature does make a difference too. Air mass is rarely bothered with as the coefficients are almost negligible.

Thanks SiberSolar,

what are the possibilities for this kind of situation ? given that the irradiance is around 800W/m2, TempAmb is 45, etc. and the Isc from the nameplate is (say 9A) and when we test the string we are only getting around 3A.

 

[SibertSolar]

Can you describe how you are performing the test on each string?

 

[squelch]

using the Seaward 150 instrument. will it be in connection with insulation or module damage ? just guessing not sure of this.

 

[SibertSolar]

Ok, are you still getting the voltage values you would expect, under load and also open-circuit? At 45C cell temp, and around 800W/m2 irradiance, you should be getting more than 3A I would expect. Are you sure about those temp/irradiance values though?

 

[squelch]

Ok, are you still getting the voltage values you would expect, under load and also open-circuit? At 45C cell temp, and around 800W/m2 irradiance, you should be getting more than 3A I would expect. Are you sure about those temp/irradiance values though?

thanks Sibersolar for this responsive message on my question.
this situation is for " What if it happens ? " im just seeking informations if this scenario may came up on our future installations.

those numbers are imaginary one's just for sample.

 

[SibertSolar]

ok, understood. In that case, if you do find that the measured Isc value doesn't reflect the extrapolated value expected, based on the environmental factors present, then that would typically indicate cell or module power issues, which would need to be investigated on a panel by panel basis, using systematic (step-by-step) trouble-shooting methods to identify why the irradiance present is not resulting in the right levels of current output.

More often than not, issues with modules, wiring, connectivity, fuses, etc, etc are manifested by a voltage problem, not current. For low current issues, you would need to look at the possibility of defective bypass diodes perhaps, or defective module sub-structure (internal parallel connections, cell defects, ribbon connection defects in junction box etc, etc

Difficult to be more specific in such a hypothetical scenario I'm afraid.