EB55 with 200W solar panel only charging at 25W

i have just tested a brand new 200W solar panel to charge my EB55 and it only produced 25W with direct line of sight of the sun and over 30 degree celsius. So it is pretty good weather right now for solar generated power.
How do i test which of the components is the culprit here?


Please share the model of solar panel you’re using?

  • Always double check a panel’s Open Circuit Voltage “Voc” and be sure to be within your EB55’s max input range of 12-28V.
  • Voc is the “open circuit” voltage, meaning the maximum voltage the panel can produce. It has to be lower than the maximum your EB55 can take, or you might damage or even fry your unit.

Unless you’re sure of the quality of your solar panel, we should check it first. See the 3 test I suggest below.

  1. Begin with an open-circuit voltage check in good sunlight; it’s, probably the easiest test. See my small ETFE panel below connected to a multimeter (in DC mode, parallel):

In (very) good sunlight conditions, it should be close to the panel’s Voc.

  1. Test the current under load, with good sunlight. Testing the current is a bit more complex as it needs a DC load that supports your panel’s voltage. There, you put your multimeter in series between the panel and the load.

The current can’t go higher than the Imp (intensity at maximum power) indicated on the label at the back of your panel.

  1. Test the voltage of your panel under load. Connect your panels to a load and check the voltage at the terminals.

It’s important to note that the reading here is always lower than the Voc you tested in step 1. It can’t go higher than the Vmp (Voltage at maximum power) indicated on the label at the back of your panel.

This way, you can test 3 important aspects of your panel in conditions that you think are good (clear sky, noon sky, panel perpendicular to sun, no shade, clean panel surface, etc.).


For example, I’ve obtained some 100W ETFE panels from Aliexpress (punchline: don’t buy those). Just see the label at the back (and mind the “fiexible solat panel”):

At 65€ a piece, it looked like a decent deal for portable panels (<2kg per unit). However, thoroughly testing them revealed they don’t match their advertised spec at all.

The real values I got from testing this one were:

  • Max power 65W (instead of 100)
  • Vmp: 13,5V
  • Imp: 4,25A
  • Voc: 18V

BTW, don’t trust the announced rating on sites like Amazon and Aliexpress from brands that are not popular yet. The example above is a lucky pick in spite of generating only 60% of announced capacity. I’ve seen panels announcing 200Watts, but in reality, only generate a bit more than a dozen Watts. Few considerations:

  • top-tier, roof grade panels should generate about 200-220Watts per square meter
  • heavier panels like roof grade usually have better sensitivity, but then, it’s 20-25kg for 400W.
  • a lightweight panel (<5kg / 100W) that is rated above 150W per square meter is suspicious in my experience.
  • before buying an unkown brand, always consider this.

Another thing to check is what you consider “good conditions”. Vendors might challenge that too. It’s probably trickier because you need other panels, ones that have proven their worth. Here’s a rough test setup I use to have a general idea of how well panels perform:

These are 2 pairs of different flexible panels and a roof-grade Longi panel. Longi is like Trina, Denim & co, it’s top quality for an unbeatable price (<30cents per W) and I’ve tested a lot of those. They easily reach 99% of advertised power output in what I call “good sunlight” (Europe, Brussels: May to September, blue sky, sun, no clouds, easy).

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Hello and thanks,

Sorry for not including any information about the panel in the first place. It is bought on amazon germany. I thought/hoped 180+ ratings with a median of 4.5 stars will get me a usable product.
But the specs on the back of the panel don’t even match the specs on the amazon page https://www.amazon.de/dp/B08QZPYN1L?psc=1&ref=ppx_yo2ov_dt_b_product_details
But the Voc is still within the EB55 required range.
I don’t have a set of solar panels to test with, this is my first attempt on this topic.
I’ll try the open circuit voltage check.

Thank you

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@uhtred You can test the voltage of the solar panel with a multimeter to check if the solar panel works. If there is no problem with the solar panel, then the solar charging cable maybe defective.

Just to verify…the battery is not almost fully charged an unable to accept much is it?

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it’s down to 40%, there is room for power.

Guys, i returned the panel and ordered another one with better reviews. It performs very good. So i assume the first panel was rubbish.
Thanks for your support

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So the fault was with an aftermarket solar panel and not a problem with the Blueti in any way?


Yes, the 3rd party solar panel was at fault.

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