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Ebay "Camping Solar Panels" listings with impossibly high power ratings

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ozzee:
I'm in the market for some solar on my upcoming but now postoned due to covid19 camping trip.

Blindly I decided to get some "flexible 300W" panels. I did a quick current measurement and found they barely produce 130W. I'm now on my fourth purchase of panels and it's not looking good.  I had one listing saying it was 24% efficient but there's no other production panels saying 24% efficiency.

I escalated this to Ebay and they basically said "we're working on it" and failed to shut down any of the listings as far as I can tell.

Is this a common problem?  I have roof panels and they produce close to their rated power even in mid July.

I've referred this to NSW Fair Traiding so hopefully I'll get an answer in a couple of days.

Maybe Dave can do a Camping Solar Panel shootout and see what Ebay does about it then...

BCF has similar panels but their power ratings seem to be much more reasonable and likely correct. Their prices are less competitive but at least you can hope to get what you paid for.

BrokenYugo:
It can generally be assumed that Chinese watts are about half the size of a regular one.

beanflying:
Current measurement under what Voltage conditions for what panel/controller?

With Solar you need to look at a complete spec at best efficiency point and also ensuring you are facing the Sun and putting in a nominal 1000W/m2 before deciding if a given panel lives up to a claim or not. Simply stating a Current while the rest of your system (charger/controller/battery etc) is pulling the Panel below MPP wont really give you a complete answer.

Even doing all that properly I would tend to still be 20-30%+ skeptical about evilbay claims for performance.

ozzee:
One instance:

Looking at the power leads connected directly to the panel. A fully illuminated panel perpendicular to incident midday sunlight with a rated short circuit current of 17A delivers 7.8A. I'm pretty sure that being in the middle of winter does not make a 55% difference in power generation. The nominated max power voltage is 18.4V so the upper limit power is 144W, probably more like 125W when you take into account the drop in current from short circuit to 18.4V. These panels are listed as 300W and they're about 1m2 in size (the active power generating PV area a little smaller.) Hence, at 300W these panels would need to be around 30% efficient based on the listing's provided specifications. And; they're German certified, I forgot to mention that.

Maybe the sun shines brighter in China?

beanflying:
If you are looking at the leads you are not looking at a short circuit you are looking at two low value resistors plus whatever connectors and fuses are fitted. While it won't make a lot of difference it is still is important how you test in particular when you get above a few Amps.

In particular at or around zero volts the burden voltage of your meter will never read close to accurate as it too is a resistor (unless you are using a hall effect or similar one). Depending on your meter and the leads on it your actual error might be a lot https://zone.ni.com/reference/en-XX/help/370384V-01/dmm/burden_voltage/ Typical DMM leads unless very high grade above a few amps are never going to give a decent result even at higher voltages (non/near shorted).

The main point is here testing method and equipment and how it is used is important. Typically an external shunt should be used and clamped across the panel and then the voltage across that shunt measured to get a current reading.

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