Solar panel output too low?

[tsizkeik]

So I bought 4 100 watt flexible solar panels of banggood
Elfeland sp-37 (here is the link, dont know if it will work for you) https://www.banggood.com/Elfeland-S...line-Solar-Panel-p-1143245.html?rmmds=myorder
I installed them and got a victron 100/50 mppt smartsolar thinking that I will eventually expand to rigid panels on a rollbar.
They are currently on my bimini.
I have been monitoring their output, their highest was 126 watt and that only lasted for a few seconds. They average between 70-90 watt.
I use 6mm2 cables about 6 meters lenght between the panels and the MPPT and 10mm2 cables about 5 meters length between MPPT and batteries.
I have tried both series and parallel connections and there was little difference between them, could even be the movement of the boat that caused the difference.
I am baffled. I was not expecting them to be as productive as high-end ones but surely I should be getting 50% of their nominal wattage, right? I am in Greece and above output as for August.
What am I doing wrong? There maybe a way to further shorten the cables by another 2 meters but that's about it. And at 5-7 Amps output given the cables sizes I don't think that will make a big difference.
Reading around online I think I should be getting around double the output I am seeing at the moment, right?
I just installed a VE150 Isotherm fridge, replacing my SeaFrost and the solar can barely keep it running.
What are you guys seeing from your flexible solar panels?
Thank you
Dimitri

 

[Daverw]

What voltage is the controller reporting in full sun?

 

[tsizkeik]

Max voltage averages between hi 17 and low 18 volts, but usually its around 14-15 volts 4-5 Amps. At the same time I get around 13 volts 5-7 Amps on the battery side output of the MPPT. But I guess that is normal voltage, right?

 

[Daverw]

13v seems a bit low to charge batteries, can you adjust it. Fridge may need about 5-6 amps when running, have you checked what needs.?

 

[tsizkeik]

A typical day

 

[tsizkeik]

When the battery starts off at 12.20 in the morning, the charger will give it about 12.8. As the battery slowly charges, the charger gives it more juice, all the way up to 13.8 at mid day. The charger is set up for Victron AGM which is the closest to my Bosch Deep Cycle of all the Victron presets ( I tried contacting Bosch with very specific questions about charging the batteries but never got anywhere with them, both their Greek rep and the German head office, will be chasing them on). Unless I am grossly mistaken, the MPPT is correctly setup and the panels just do not produce. I know they can produce because they give me peaks of 110-126 watt momentarily but like I said, 70-90 average. They are only shaded by the twin backstays but surely even at 35 degrees ambient temps they should not lose around 80% of their nominal wattage (i am talking about mid day). 50% i would consider ok but 80%? And if panels are at fault, how come i see spikes of productivity and then revert back to their average?

 

[VicS]

So I bought 4 100 watt flexible solar panels of banggood......................
Dimitri

I think in full sun in Greece you ought to get the full rated output if they are facing the sun and not shaded, Your wiring appears to be adequately sized,

Are your batteries capable of accepting the expected max output from the solar system. Are they of sufficient capacity and are they discharged sufficiently.
If the batteries are too small or are almost fully charged already they wont accept the full rated solar output.

Is the Victron operating in "bulk mode"

Are the batteries getting old and not accepting the charge current they should do

 

[tsizkeik]

2x140 Ah Bosch Deep Cycle, 3 years old, when not in use they get to absorption and float within a single day according to the Victron. They are not new but I would say they are about 85-90% of their original capacity at least. Never had them below 12v and where usually charged by 2 oclock before adding the fridge. The fridge draws 5-6 amps indeed, working for 20 min every 1andahalf hours during daylight, about 10 minutes every 2 hours give or take during night time. My icebox is very well insulated.

 

[Daverw]

As VicS says, are your battery’s actually near full charge and reducing input, you are only looking at the input in isolation, what happens if you let the batteries discharge a little more that put the solar back on?

 

[tsizkeik]

If you see the pics I posted, I start off at 12.10-12.20 in the morning. With such a tiny solar output, it is impossible that the batteries will be near fully charged by mid day when full power is available from solar panels. But if we suppose you are right, that would mean that the batteries would eventually be fully charged at some point, correct? What usually happens is the batteries are around 12.6-12.7 by late afternoon and back to 12.10-12.20 in the morning since I never switch off the fridge ( I could do but I wanted to find out how much power I would need on 24hrs bss). I get what you are saying but that would only happen if the batteries were nearly fully charged and the MPPT would limit itself as it would start its 6 hour absorption cycle. Like I said, that is exactly what happens when the fridge is off. If I understand correctly even in the heat of the summer I should be getting close to 400 watts for at least 1-2 hours a day, when sun in vertical to the boat, right?
Apologies, overlooked the question, yes the Victron is working on bulk mode throughout the day

 

[PaulRainbow]

As VicS says, are your battery’s actually near full charge and reducing input, you are only looking at the input in isolation, what happens if you let the batteries discharge a little more that put the solar back on?

More than the 50% discharge they are suffering now ?

 

[William_H]

First thing for OP to do is in full sun load up the electrical system as much as possible with lights pumps fridge and inverter all pulling as much as possible. If this can be done initially with solar charge off then turn on solar and he might get close to max from the solar system. Proving it is OK. if not....
Second thing for OP to check is the panels them selves. Isolate each one and check open circuit voltage in the sun. This should be around 20 volts. Then use your multimeter on amps scale (10 amps) to short out the panel. (disconnected from the controller) He should get around 5 amps short circuit. No this will not harm the panel. If these 2 tests prove OK on all panels then OP is expecting too much of the system. I would guess that controller is not pushing enough voltage into batteries and or batteries are not accepting the charge current he expects.
It may be a case like having a 100amp alternator and asking why he does not get 100 amps charge. (because the batteries and system can't use the 100 amps). ol'will

 

[tsizkeik]

That is what i plan to do next time im on the boat, i simply did not have the luxury off taking them offline and check them. My alt is 40 Amps and the batteries can keep up. My shore charger is 30 Amps. I was just trying to find out what others are getting from their panels and was wondering why I get peaks of 126 watts and then reverting to 70-90 while there is no shading involved. I did test the open voltage before installing them and it was indeed over 18 volts but being cheap my multimeter only reads tiny amounts of Amps so had no way of checking that. I now have a proper multimeter and will check them.
Quick question. If indeed they output over 5 Amps upon checking, what do I do next?

 

[Mistroma]

I tried a different type of flexible panel on the awning a couple of years ago. It worked well for a few weeks and then output dropped sharply. It was replaced under warranty and the replacement also failed.

I had given the supplier full details of the installation and they had initially claimed it was suitable for mounting on a bimini. However, their advice had changed when I checked a few months later. It said that the panel must not be allowed to sag in the middle to give a concave curve. Convex was OK as this stretched the cells very slightly. Concave compresses them and this causes micro-fractures and output drops off very significantly.

No idea if this will apply to your panels but I imagine it is a general rule that a concave curve will compress the top layer and cause issues, especially when it is moving up and down slightly. Do your panels droop in the centre or are they supported in the middle with a metal frame?

N.B.
My daily output from rigid panels in Vlycho yesterday was:
1) 39Ah from 145W under the boom (PWM)
2) 80Ah from 200W on arch at the stern (MPPT)

I don't log details of current but did see 6-7A from 145W and 10A from 200W at times yesterday. Very variable as the boat was slow turning round in circles all day.

 

[tsizkeik]

Thank you for the numbers.
My panels do not droop, if anything they are convexing as the bimini is super tight. I also thought about that by reading about it online.
i have never seen decent output so as to believe that the panels where ok but somehow the performance dropped.

 

[noelex]

That output is much lower than expected. A peak of 126w from 400w is very poor and indicates something is wrong.

A good test of the panels, and the overall installation is that under very good solar conditions the peak maximum output should be close to rating of the panels. Often this peak reading will only be brief, typically as the sun comes of of cloud (the cloud edge effect), but this provides confirmation that everything is working as should do.

It is time to conduct the tests that William has nicely outlined in post #12. I suspect these tests will show the solar panels are defective.

 

[lawrence_craig]

I am not going to contribute much as the people that have contributed so far to this thread know way more than me on this subject but if it's any help:

I am having exact same issue. I bought 300W of solar panels (semi flexible) and in the Caribbean, only achieved max 200W. In Europe, I am only getting 100W max. I have recently changed my batteries (all new) and performance hasn't changed. I personally think I there's an issue with my solar panels (got them off Amazon) but I am still testing. They are similar to yours if that makes a difference.

Not much help but you're not the only one out there.

 

[tsizkeik]

My friend, just the fact that I am not the only one there makes me a lot happier. I was going crazy over this. We do a lot of electricity physics at school in Greece and I was an ace student so my brain would not give up on this. Many a sleepless nights were wasted trying to understand what I have done wrong. Thank you

 

[lawrence_craig]

Haha I know that feeling.

I had a thread running on another forum with the exact same question/problem. http://www.cruisersforum.com/forums/f14/solar-performance-in-the-med-222712.html

Still trying to work it out however so will watch this thread with interest.

 

[Bobc]

I have a cheap 100w semi-flexible panel from China and a Victron 75/15.

I only typically get about 20-25w at 14.5v in the middle of a clear sunny day.

I think maybe the cheap panels are rubbish.