getting rated power out of panels

[solar_gest]

Hello Guys,

I got some flexible panels from china, reviews are good, when I tested them I couldn't even get the Isc amperage or Voc to the specs.

do you know a quick test to check if the panel is actually able to output the power according to the stated specifications?
I see many youtube videos where a 100W rated panel give 100W of power (also one of Will) , is that the norm or more the exception?

If I test on a full sun day, at sun peak, i should be able to get at least the current specified at max power point, right?
According to the IV curve , even if the panel voltage is lower than Vmp the current should actually be higher.

please correct me if I'm misunderstood something.

thanks

 

[nosys70]

Voc means nothing, just put a resistor in a water bucket and measur volt and current.

 

[solar_gest]

So of course I put a load on the panel and was getting 2.5A where Isc = 3.17 A and Imp is slightly above 3A.

I would expect that under full sun, clear sky a min of 3A, is that correct? Even if the voltage is say 3Volts if I have a 1Ohm resistor.

in my test the voltage was around 14Volts with 2.5A. I understand it will not be max power, but the current should be at least 3A no?

 

[nosys70]

no, even in good condition it is possible to have far less than 100% of the written specs.
i would say even more if specs are set by some chinese guy.
65 to 85% is usually what you get.

 

[gnubie]

Only if the load can pass sufficient current to pull the panel down to or below Vmp. If the panel voltage stays over Vmp regardless of light exposure you will not see the full current the panel can produce.

Under STC if you short the panels you should see Isc. If you don't the specs on the panel are incorrect. The question is, do you meet the STC?

 

[gnubie]

no, even in good condition it is possible to have far less than 100% of the written specs.
i would say even more if specs are set by some chinese guy.
65 to 85% is usually what you get.

Choice, the arguably premier consumer magazine in Australia, tested a whole heap of panels on sale in Australia and found that over 70% of them did not meet their claimed ratings.

 

[ianganderton]

What would be a simple setup to test solar panels? What’s the best way to safely create a load so maximum volts and amps could be measured?

 

[Forbisher]

in my test the voltage was around 14Volts with 2.5A. I understand it will not be max power, but the current should be at least 3A no?

14V x 2.5A is 35 watts.
What is the panel rated for?
And what are the dimensions and cell count?

 

[gnubie]

What would be a simple setup to test solar panels? What’s the best way to safely create a load so maximum volts and amps could be measured?

If you are chasing the Vmp and Imp you may find a cheap MPPT controller with a front panel display is the easiest way. Connect a load to soak up all the panel's output, a partially discharged battery etc, connect panel and observe what the MPPT controller says. You could fiddle around with resistors, meters, buckets of water and such but compared to just hooking it up to a MPPT controller, that's more effort in my books.

 

[Hedges]

What would be a simple setup to test solar panels? What’s the best way to safely create a load so maximum volts and amps could be measured?

Max volts and amps is trivial. Vmp and Imp is a bit tougher, but it is an exponential curve and those set endpoints. I just assume ratio of maximum power to Voc x Isc follows data sheet.

I had some spare Square-D heavy duty disconnects (3 poles, unfused, 600V AC/DC, 30 A) so I put in MC4 pigtails and banana pigtails.
My the banana plugs to in my DMM common, volts, amps. With switch open I connect a PV panel, note Voc. Close the switch, note Isc

Here was my setup:

 

[solar_gest]

thanks for the answers.

I have a flexible panel, brand new (at least supposed to be)

14V x 2.5A is 35 watts.
What is the panel rated for?
And what are the dimensions and cell count?

55W , dimensions 565 x 530 mm, 32 SunPower Cells.

no, even in good condition it is possible to have far less than 100% of the written specs.
i would say even more if specs are set by some chinese guy.
65 to 85% is usually what you get.

I saw several youtube videos, one of them a guy (Julian Ilett) even in UK was getting 20w from his 20W panel . I live in northern italy would expect the sun to hit harder in summer.
But if you guys think this is normal, I'll acknowledge this. I'm new to the whole solar thingy.

 

[gnubie]

It depends on the quality of the cells, and if the seller is even being truthful about the capabilities. Anyone can order a pallet of 175W panels from China and ask that the label have specs for a 300W panel printed on the label. If you pay attention to cheapie panels the labels haven't even been screened, instead they are ink dot matrix printed, complete with spelling mistakes at times too.

The physical dimensions of your panels vs claimed wattage is believable, but that depends on the quality of the cells and the amount of area that isn't actually covered by cells. They state sunpower cells, a good name, but there's no guarantee they actually are unless you can trace their heritage. I've seen panels claiming kyocera cells, visually they obviously weren't.

 

[Hedges]

thanks for the answers.

I have a flexible panel, brand new (at least supposed to be)



55W , dimensions 565 x 530 mm, 32 SunPower Cells.




I saw several youtube videos, one of them a guy (Julian Ilett) even in UK was getting 20w from his 20W panel . I live in northern italy would expect the sun to hit harder in summer.
But if you guys think this is normal, I'll acknowledge this. I'm new to the whole solar thingy.

I was wondering how they arranged 32 cells to make a square panel.
Turns out it is like KFC's "10 pieces of chicken". They cut each of what we would call a piece in half, and technically they now have twice as many pieces.

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Depending on how wired, that might or might not help with partial shading. Bendability? Only helps in one direction.

Apparently some of these little panels are branded SunPower, while others are made from SunPower cells.
Everybody knows that matching cell current in a panel maximizes power, because the panel will be pulled down to lowest current of any cell.
Same goes for panels in a series string.

Probably many manufacturers buy cells, assemble panels, and (if you're lucky) rate the panel according to stated power of the cells.
Real panel manufacturers flash test the panels to measure output. That is after they bin cells, so they can assemble some panels for higher power and charge accordingly. At the low end of products, of course they would just slap them together fast.

You can easily have been testing on a day when sun was < 1000W/m^2. We assume you oriented the panel directly toward the sun.

"I live in northern italy would expect the sun to hit harder in summer."

Ahh, there's your problem. We tell Italian jokes over here.
The sun probably did hit harder in the summer. You got Isc = 79% of label rating, which represents 1 standard sun and panel at 25 degrees C.
Try cooling it with air conditioner or whatever, then measuring immediately upon aiming it directly at noontime sun. Although, apparently heat has more impact on Voc and power than on Isc. You may have about 800W/m^2 rather than 1000W/m^s

https://image.slidesharecdn.com/blobservere20-120418175716-phpapp02/95/pv-option-2-e20-data-sheet-2-728.jpg?cb=1334772744

Did you test all panels? That would rule out single defects (but would follow variations in lowest-output cell, at least at Vmp)
Measure current shorted, which should be less sensitive to temperature. Power, and current at around Vmp, will definitely be lower when hot.

 

[solar_gest]

Thanks @Hedges for the long answer, appreciate.

I also was wondering how they can state 32 cells , and yeah the panel is same type as you posted in your second link. They are cut into halves.
I tested also shading, if I cover 1cell , 0 amperage.
If I put my hand above the panel, amps also drastically drop almost to 0. So no bypassing there lol.
I also got a 110W panel which has the 32 entire cells, and it s double the size , obviously.

I ordered from a manufacturing company, so they (say) buy SunPower cells from US and assemble them there in China. I have tested 4 50W/55W panels. Next week will try the 110W ones.
Panels were not too hot as I just take them out for testing and cover them when finished so they cool down. I also cleaned them with cold water to make sure no debris and to cool them further down.


Anyway the fact of 1000w/m2 was taken for me as granted, i thought that at our latitude we would be getting more in full summer on a clear day, especially after some vids i saw.

I was clearly wrong, i researched and found the solar irradiation from EU meteo SAT, so you are right, we are having between 800-900W/m2
Here the link of today
EUMETSAT solar irradiation

And here screenshots of it for 1pm and 2pm CET timezone. Clearly below 1000W/m2.

So my measurements kinda make sense now, still surprised, but it s ok.

I m puzzled how Julian ilett could in UK gets max. i mean UK!! Of course it s not today and who knows when the vid has been taken, if I find the link i ll post it. Cant believe they ever get 1000W/m2 LOL.
He s not the only one posting vids where you can see max power extracted from solar panels, but doesn't really matter anymore.

I ll post the result next week of the 110W panels and hopefully the italian jokes are funny over there and not so lame as here haha

 

[gnubie]

Julian can get that, on the odd occasion he even has direct sun considering the amount of cloud he has to put up with, because of the typically lower temperatures he has. His panels are cooler. Cooler panels = more power. Sure it can get hot-ish in the UK but their sweltering heatwave conditions are other place's cool spring days.

 

[Hedges]

I also was wondering how they can state 32 cells , and yeah the panel is same type as you posted in your second link. They are cut into halves.

Actually, there is a reason for that. "12V" panels are either 32 or 36 cells. If they hadn't cut the cells in half and wired them in series, you'd only get about 10V and they couldn't charge a 12V battery without a boost converter. Of course, they're made with a cell that's popular for larger panels. And the pieces cut off to fit a round peg in a square space get put in even smaller panels.

 

[solar_gest]

Julian can get that, on the odd occasion he even has direct sun considering the amount of cloud he has to put up with, because of the typically lower temperatures he has. His panels are cooler. Cooler panels = more power. Sure it can get hot-ish in the UK but their sweltering heatwave conditions are other place's cool spring days.

Would cooler panels get you that much more power ? Like 20-30%? Looking at the IV curves, seems to me strange that a 700-800w/m2 IV curve would be higher as a 1000w/m2 one, because of cooler panels.
Plus I have tried my panels directly in the garden, directly pointing the sun, temperature would have had no effect in my case since i just took then out to test, so say a couple of minutes. Even that, the current doesn't reduce with higher temps. According to the datasheet.

I highly doubt you ever get 1000w/m2 in UK, just bcs of it s latitude. If you compere with continental Europe, there s a massive difference.
Anyway, here s the link, minute 3:52
Utube vid

Seems he s not even surprised, sun gets out he gets 20W.
Maybe his measures are not that accurate, especially if fiddling with an arduino. In any case, doesn't matter really, thanks for all the answers , really helped to clear some misunderstandings

 

[solar_gest]

Julian can get that, on the odd occasion he even has direct sun considering the amount of cloud he has to put up with, because of the typically lower temperatures he has. His panels are cooler. Cooler panels = more power. Sure it can get hot-ish in the UK but their sweltering heatwave conditions are other place's cool spring days.

Would cooler panels get you that much more power ? Like 20-30%? Looking at the IV curves, seems to me strange that a 700-800w/m2 IV curve would be higher as a 1000w/m2 one, because of cooler panels.
Plus I have tried my panels directly in the garden, directly pointing the sun, temperature would have had no effect in my case since i just took them out to test, so say a couple of minutes. Even that, the current doesn't reduce with higher temps. According to the datasheet.

I highly doubt you ever get 1000w/m2 in UK, just bcs of it s latitude. If you compare with continental Europe, there s a massive difference.
Anyway, here s the link, minute 3:52
Utube vid

Seems he s not even surprised, sun gets out he gets 20W.
Maybe his measures are not that accurate, especially if fiddling with an arduino. In any case, doesn't matter really, thanks for all the answers , really helped to clear some misunderstandings

 

[gnubie]

Current may actually increase ever so slightly, but temperature's main effect is on the voltage.