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  1. #1
    Join Date
    May 2018
    Posts
    45

    Default Solar panel output too low?

    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-SP...?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

  2. #2
    Join Date
    Nov 2016
    Location
    Lincoln
    Posts
    890

    Default Re: Solar panel output too low?

    What voltage is the controller reporting in full sun?

  3. #3
    Join Date
    May 2018
    Posts
    45

    Default Re: Solar panel output too low?

    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?

  4. #4
    Join Date
    Nov 2016
    Location
    Lincoln
    Posts
    890

    Default Re: Solar panel output too low?

    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.?
    Last edited by Daverw; 28-08-19 at 22:54.

  5. #5
    Join Date
    May 2018
    Posts
    45

  6. #6
    Join Date
    May 2018
    Posts
    45

    Default Re: Solar panel output too low?

    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?

  7. #7
    Join Date
    Jul 2002
    Location
    Home: Kent. Boat: Chichester
    Posts
    43,614

    Default Re: Solar panel output too low?

    Quote Originally Posted by tsizkeik View Post
    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
    Last edited by VicS; 28-08-19 at 23:11.

  8. #8
    Join Date
    May 2018
    Posts
    45

    Default Re: Solar panel output too low?

    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.

  9. #9
    Join Date
    Nov 2016
    Location
    Lincoln
    Posts
    890

    Default Re: Solar panel output too low?

    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?

  10. #10
    Join Date
    May 2018
    Posts
    45

    Default Re: Solar panel output too low?

    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
    Last edited by tsizkeik; 28-08-19 at 23:33.

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