Solar power questions.





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  1. #1
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    Default Solar power questions.

    Hi All
    Sorry to bring this topic up again but I'm in need of a bit of clarification.
    I have done my sums and decided I need 100 watts. To make vehicle packing a bit more compact I intend to buy two 50 w panels instead of 1 x 100w. My questions relative to this....
    1) If I parallel wire the two panels does that mean I will get the total amperage from the two panels combined, that is about 5.5 amps, or will 1 x 100w panel be more efficient?
    2) Now I see that some panels are rated "18 volts" - what does this mean? My limited experience with (house) solar panels revealed these putting out anything up to 30 volts?
    3) Do I need 4mm or 6mm cable from panels to controller?
    Thanks again in advance.
    Fish

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  3. #2
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    Default Re: Solar power questions.

    For your application it will make no difference if it's 1x 100w or 2x 50w panels. You will need to parallel them if you are presumably using a PWM controller to charge the battery. The 18 volts is a no load voltage, no problem.
    I must however say that 100w is very little and if you have a cloudy day (even one) you are going to run low on power .... You should really aim for more like 160w to even start feeling safe.

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  4. #3
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    Default Re: Solar power questions.

    18V tells you it is an 12V panel.

    4mm wire is fine
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  6. #4
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    Default Re: Solar power questions.

    Thanks Dave and Prof
    Dave, I just need to power a 40ltr. fridge/freezer when I'm camping in game parks. I've already got a NL dual battery system fitted. Considering that I will do at least a 40km game drive EVERY morning and again in the afternoon, I felt that a 100w panel would suffice to top up when not driving around? I intend to use a MPPT controller. Do you still feel I need more wattage ?

  7. #5
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    Default Re: Solar power questions.

    So here is my view.

    You will loose about 20% when putting them in Parallel, I have done the same with two 100W panels, I should get around 15Amps but I get closer to 12amps, I have tested both panels separately and get around 7.5amps.
    Remember the change controller will charges at between 13.2 and 14v. So 100w will give you around 7amps per hour. Depending on the age of your fridge you are looking at a hourly draw of around 5amps. A 100AH will only give you 50Amps worth of power MAX so work on needing 120amps per day to run for 24h a day at 5amps. So to get enough of a charge during the day to fully change your battery and run the fridge, I would say look at the 200W's of Solar panels. This is worse case.

  8. #6
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    Default Re: Solar power questions.

    Quote Originally Posted by shfish View Post
    Thanks Dave and Prof
    Dave, I just need to power a 40ltr. fridge/freezer when I'm camping in game parks. I've already got a NL dual battery system fitted. Considering that I will do at least a 40km game drive EVERY morning and again in the afternoon, I felt that a 100w panel would suffice to top up when not driving around? I intend to use a MPPT controller. Do you still feel I need more wattage ?
    Agree on the 100 Watt as described above.
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  9. #7
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    Default Re: Solar power questions.

    I sell 2 x 55W suitcases with 10m Extension (6mm˛) - Durbanville



    Please view this ad:

    110W Solar Panel Suitcase (2 x 55W Mono) with 10m Extension (6mm˛),
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  10. #8
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    Default Re: Solar power questions.

    @shfish,

    I specifically made the 2 x 55W suitcase for my dad with his Suzuki Jimny (60L Fridge and few led lights) and National Luna box.
    He's more than happy with this setup
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  11. #9
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    Default Re: Solar power questions.

    100W is more than enough to run a fridge for the day.

    I have run a fridge AND a freezer in 40 degrees weather off 2x50W panels for the day, was cutting it very close though and the battery was maybe at 80% full at the end of that day.

    I have my 2x50W panels in series into a Victron MPPT regulator. That regulator can take up to 75V input (2 panels are 2x 18V = 36V). My thinking was that if the voltage is higher (panels in series) there are less losses in the cable from the panels to the regulator.

    With this setup I'm getting a good 7.0 Amps into the battery at 14.3V.

    As an experiment I connected the panels in parallel, same position, same time of the day, same load... still got 7.0 Amps into the battery at 14.3V - tells me the difference between series or parallel connection is negligible.

    BUT, the biggest improvement in a solar setup like this is the MPPT regulator, it's really worth the money!!


    Additional thought: You get the most from a solar panel if you can always point it directly to the sun. If you want to fix it to your car's roof, then you might have to consider going bigger because you wont always get max power from the panel with the angle of the sun changing through the day.
    Last edited by guido.e.koch; 2020/03/04 at 10:36 AM. Reason: additional thought
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  12. #10
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    Default Re: Solar power questions.

    Start out with 100W and see if it works for you, but spec your MPPT controller to be able to handle more, in case you want to go bigger in future.

    I'd say get yourself a controller which can handle at least 20 amp, but even 30 amp won't hurt depending on price difference. With a 20 amp controller, you'll be able to go up to around 350W if wiring 12V panels in parallel.
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  13. #11
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    Default Re: Solar power questions.

    Thanks for all the input/advice everybody! I think I've decided on my set-up........it's just the contrasting views on the required wattage that's left me in a quandary!

  14. #12
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    Default Re: Solar power questions.

    Hi again All
    Sorry to be a nuisance but a new question has come to the fore with my solar addition. Just to remind you, I have a NL intelligent solenoid system powering one aux. battery. Now I've added a 100 watt panel, via a MPPT controller, to the same aux. battery. Simple question, do I attach my Fridge/Freezer directly to the aux. battery as before, bearing in mind that the intelligent solenoid protects the main battery, or do I connect the fridge to the "Load" terminals of the MPPT controller coming from the solar panels? Or does it not make any difference?
    Thanks in advance,
    Fish

  15. #13
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    Default Re: Solar power questions.

    Quote Originally Posted by shfish View Post
    Hi again All
    Sorry to be a nuisance but a new question has come to the fore with my solar addition. Just to remind you, I have a NL intelligent solenoid system powering one aux. battery. Now I've added a 100 watt panel, via a MPPT controller, to the same aux. battery. Simple question, do I attach my Fridge/Freezer directly to the aux. battery as before, bearing in mind that the intelligent solenoid protects the main battery, or do I connect the fridge to the "Load" terminals of the MPPT controller coming from the solar panels? Or does it not make any difference?
    Thanks in advance,
    Fish
    If you connect it on the load terminals the controller will disconnect the load when the battery are running low. If your fridge have such option then it does not matter
    Last edited by JLK; 2020/03/17 at 07:32 PM.
    Johan Kriel

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  17. #14
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    Default Re: Solar power questions.

    Ok, thanks JLK.
    My fridge does have that cut-off protection, together with the NL intelligent solenoid so it seems I can connect the fridge either way.
    Regards.

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