label at solar panel

[thebe]

Hello masters,

I am new here.
I already bought solar panels. There are some items written on the label.
How the manufacture get the numbers such as Wattage, Isc and Voc?
Is it an actual value of the panel?

Regards,
TB

[PNjunction]

Yes. At least from what they test at the factory during the "flash" test. Real world is usually a tad lower.

Here are some generalities:

ISC is current-short-circuit. You can short a panel without destroying it. If you want to test it you put an ammeter (or multimeter in the current measuring mode first) inline between the two leads. Cover panel with a towel beforehand, and once all connection are made, remove it.

VOC is voltage-open-circuit. That is, there is no load or other connection to the panel. Put a multimeter on the voltage scale across and measure.

Wattage is VOC * ISC. Part of the power forumula, P/I*E

[thebe]

Yes. At least from what they test at the factory during the "flash" test. Real world is usually a tad lower.

Here are some generalities:

ISC is current-short-circuit. You can short a panel without destroying it. If you want to test it you put an ammeter (or multimeter in the current measuring mode first) inline between the two leads. Cover panel with a towel beforehand, and once all connection are made, remove it.

VOC is voltage-open-circuit. That is, there is no load or other connection to the panel. Put a multimeter on the voltage scale across and measure.

Wattage is VOC * ISC. Part of the power forumula, P/I*E

Thanks a lot with the info.
But why the label value is always same one to the another?
Is the value just a sample data of one panel, then we just generalize and write it to another panel?
So the other panels have same data.

[foo1bar]

Thanks a lot with the info.
But why the label value is always same one to the another?
Is the value just a sample data of one panel, then we just generalize and write it to another panel?
So the other panels have same data.

It's probably not the same across all the panels.
BUT it should be the same (or very close) for the panels that you buy as a group - you want to get panels that are fairly closely matched when installing them as a group.
A manufacturer may have a production line where they get 275W panels and 285W panels and 295W panels.
The lables for the 275W panels will all be the same, as will the ones for the 285W and 295W panels.
But the label will be different for a 275W panel compared to a 295W panel.
The exact results from testing may say that the panel labeled as 275W is actually 277W or 280W or maybe even 274W.
But it'll probably be within 4% of any other 275W panels - which is close enough that all those 275W panels from that manufacturer will work well together. (there won't be much power lost due to mismatches between panels)

BTW - Wattage shouldn't be Voc * Isc. It should be Vmpp * Impp.
Voc is Voltage-open-circuit (max voltage you should ever see.)
Isc is Current-short-circuit (max current you should ever see)
Because it's a curve, Vmpp and Impp (max-power-point) are lower for both current AND voltage than those values.
(But 0A * Voc = 0W and Isc * 0V = 0W - which is what those points on the curve represent. Vmpp/Impp is where on that curve the product of voltage and current should be at it's maximum)

[thebe]

It's probably not the same across all the panels.
BUT it should be the same (or very close) for the panels that you buy as a group - you want to get panels that are fairly closely matched when installing them as a group.
A manufacturer may have a production line where they get 275W panels and 285W panels and 295W panels.
The lables for the 275W panels will all be the same, as will the ones for the 285W and 295W panels.
But the label will be different for a 275W panel compared to a 295W panel.
The exact results from testing may say that the panel labeled as 275W is actually 277W or 280W or maybe even 274W.
But it'll probably be within 4% of any other 275W panels - which is close enough that all those 275W panels from that manufacturer will work well together. (there won't be much power lost due to mismatches between panels)

Thanks master.
For example when I bought 3 panels and test the current, I have:
Panel 1. Isc = 8.23 A
Panel 2. Isc = 8.55 A
Panel 3. Isc = 8.40 A

But at the label it is printed 8.30 on the label.
Where is the value come from?
can you tell me.

[sensij]

Isc is very sensitive to the irradiance. The mfg uses a controlled test procedure using calibrated light sources and measuring equipment. How are you controlling those things in your test?

[J.P.M.]

Thanks master.
For example when I bought 3 panels and test the current, I have:
Panel 1. Isc = 8.23 A
Panel 2. Isc = 8.55 A
Panel 3. Isc = 8.40 A

But at the label it is printed 8.30 on the label.
Where is the value come from?
can you tell me.

FWIW, besides slight mfg. variation and assuming you're measured the Isc at about the same times, but a couple of minutes apart for each measurement, part of the difference in the current you are measuring is due to the slight variation in the solar irradiance form minute to minute, and/or a slight difference in orientation from one panel to the other relative to the direct irradiance.

[foo1bar]

For example when I bought 3 panels and test the current, I have:
Panel 1. Isc = 8.23 A
Panel 2. Isc = 8.55 A
Panel 3. Isc = 8.40 A

But at the label it is printed 8.30 on the label.
Where is the value come from?
can you tell me.

IN addition to what has already been pointed out about how easy it is to have a slight difference in irradiation(lighting) of the panel, there's also probably some small amount of variation that's acceptable. 8.23, 8.55, and 8.40 are all within 3% of the 8.30A on the label.
So some of the differences in Isc could be due to manufacturing tolerance - but I'd bet most of it is differences in your testing.

[thebe]

Isc is very sensitive to the irradiance. The mfg uses a controlled test procedure using calibrated light sources and measuring equipment. How are you controlling those things in your test?

I just tested the panels using silver modules as a reference for my sun simulator. The the data that is generated from silver module is used for test my panels.

[thebe]

IN addition to what has already been pointed out about how easy it is to have a slight difference in irradiation(lighting) of the panel, there's also probably some small amount of variation that's acceptable. 8.23, 8.55, and 8.40 are all within 3% of the 8.30A on the label.
So some of the differences in Isc could be due to manufacturing tolerance - but I'd bet most of it is differences in your testing.

Thanks foo1bar. But I still confuse about getting the value that apply for all product specification(concern on Isc and Voc). Let's simplify the question, How the mfg get the value (Isc and Voc) that apply for the rest of production? Did they just take a sample randomly and took a test several times, then they average the results and define the Isc and Voc based on the average value?

[SunEagle]

Thanks foo1bar. But I still confuse about getting the value that apply for all product specification(concern on Isc and Voc). Let's simplify the question, How the mfg get the value (Isc and Voc) that apply for the rest of production? Did they just take a sample randomly and took a test several times, then they average the results and define the Isc and Voc based on the average value?

I would say that each manufacturer has a different way to test and label their panels. I doubt that every panel is put through all the same tests but my guess is they take a sampling from a production line and fully test each and then just do a go/no-go test for the rest of the panels to see if they at least function. I could be wrong but QC testing can get expensive unless it is automated.

[foo1bar]

I would say that each manufacturer has a different way to test and label their panels. I doubt that every panel is put through all the same tests but my guess is they take a sampling from a production line and fully test each and then just do a go/no-go test for the rest of the panels to see if they at least function. I could be wrong but QC testing can get expensive unless it is automated.

I would expect them to do a basic parameter test on each unit.
It'd be very much like a 'go/no-go' test - in that it'd be a very short test time.
In less than a second I'd expect them to be able to get Voc, Isc, Vmp, Imp.
They probably don't get temperature parameters for each panel, since changing the temperature takes time.

They show the testing at 4:15 in this video:

https://www.youtube.com/watch?v=BKrOZ6OogmQ

Or at ~4:33 in this one

https://www.youtube.com/watch?v=fZ1SC-vUe_I

Based on what I see as a consumer (multiple lines which look to be identical except for power production) I expect that manufacturers are sorting the panels as they test them. The ones that meet the higher wattage requirements get sold as higher-wattage panels. The ones that don't meet those requirements get labeled/sold as lower power (because they are).

I would expect that by the time a set of panels is getting ready to be sold there has been a bunch of testing on panels that should be similar to the new line of panels. I would expect that as part of manufacturing setup you'd do some example/test/sample panels, test the heck out of them, and then if everything looks good, start manufacturing in volume. And probably the labels would have the numbers from those test/example/sample panels. If the production panels were out of spec, then you'd need to look into why and address it.

Really all that Isc and Voc on that panel are for is so that the installer can use it for calculations. For example he needs to be sure that the wire is sized large enough for Isc. And he needs to make sure the voltage from multiple panels in series isn't more than 600V for 600V wiring. And that it doesn't exceed the inverter inputs. The manufacturer gives him a single value for those - which makes his life easy. in real life it's probably not "8.40" but "8.40 +/- N%" But there's more than enough safety margin that the installer can just use "8.40" and it's good enough for his use.
For example, if the Isc is 8.4A, the installer can know that he shouldn't do more than 2 strings in parallel on wiring or fuses that are setup 20A, because 8.4+8.4 = 16.6A. So he can expect 16.6A at most going through that wire, and can make sure the wire is sized appropriately (probably size everything as if it were 20A since that's the standard fuse size that's bigger than 16.6A.)