How many solar panels?

Discussion in 'Solar Power' started by StefAndDi, Jan 16, 2015.

  1. StefAndDi

    StefAndDi

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    Hello Funsters,

    I had roof-mounted solar panels fitted to my previous motorhomes so obviously I appreciate the benefits. Although my new motorhome comes with three 95Ah batteries I will have solar panels fitted again.

    My touring will be mostly in the United Kingdom, year round.

    What I need to know is: is there any benefit to me having two or more smaller panels rather than one very large one? Available space on the roof is not an issue.

    Sure some probably think that I am 'going overboard' but the way I see it you can't have too many options.

    Any observations would be gratefully received.

    Stef.
     
  2. Munchie

    Munchie Funster Life Member

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    We have 2x80watt panels and are adding another and an mppt controller!
    Our two 80's are not quite keeping up due to the low sun even in Spain!
     
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  3. Dazzlin

    Dazzlin Funster Life Member

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    I read somewhere multiple smaller panels deals better with shade as you just lose the output for the panel that is in shadow.
    It may work out heavier and more expensive though.
     
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  4. BwB

    BwB Funster Life Member

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    As many as you can fit on, is my view. They're so cheap these days. If the wattage all adds up to the same then the only advantages to many smaller panels is mainly in the event of panel failure or shade (shading even a small portion of any panel will significantly reduce its output (for most panels, some have multiple diodes)).

    However, if you're regularly on the move, battery to battery might be a better solution for you.
     
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  5. gillnphil

    gillnphil Funster

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    We have 2 x 120 watt panels and 2 x 80 a/h leisure batts. They never seem to run out of steam. We travel mainly Apl/Oct.
    Phil
     
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  6. Bluestar

    Bluestar Funster

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    Worth a read up, go MPPT control and feed with 24volt by running panels in the right series/parallel configuration.
     
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  7. TheCaller

    TheCaller Funster

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    Two smaller panels wired in series & connected to a MPPT controller that can handle the combined open circuit voltage can extract a bit more power from UK winter sun than a single panel of the same total wattage.

    Because the combined panel output voltage is now doubled for any given light level, the controller will be able to raise its output voltage above the minimum needed to start battery charging at lower light levels than with a single panel.

    In strong midday sunlight, there shouldn't be much difference between a single panel & two smaller ones, but twin panels in series should extend the effective day length a bit. Note that if you have plenty of roof space, it may be cheaper to fit more or just bigger panels with a cheaper controller than to extract the absolute maximum from two smaller panels with a more expensive controller.

    I have seen it suggested that two panels suffer less from partial shading than a single panel, but I've no idea how great this effect is.
     
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  8. Judge Mental

    Judge Mental Funster Deceased RIP

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    All these extras very nice but watch the payload.....
     
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  9. Peter A Forbes

    Peter A Forbes Funster

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    We tried panels in series, but the MPPT controller shut off above 33V, so not much good.

    The Mercedes has 4 X 100W up on the roof and two MPPT controllers in a split system. Each system has 220AH batteries.

    As solar panel cells are series-connected, if one cell fails you will lose that cell's output if it goes short-circuit. If it fails open-circuit it will prevent output from the other cells getting to the terminals.

    Shaded cells will still conduct but you'll lose that one's output.

    The four X 80W on the trailer have been reliable over four seasons.

    Peter
     
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  10. TheCaller

    TheCaller Funster

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    Hence my comment about having to use a more expensive controller. Not all MPPT controllers are made equal!

    You need to be looking at Victron or similar - & they ain't cheap! If you have the roof space, it might be cheaper to just add an extra panel. A lot depends on when & where you want to tour as well. The extra performance will be minimal if you were only to tour in summer and/or Southern Europe.
     
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  11. Peter A Forbes

    Peter A Forbes Funster

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    This is supposed to be a hobby, not a money pit! :D:D

    For our needs, the existing setup is fine, but it was worth experimenting just to confirm what we had been told.

    Peter
     
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  12. swisskenny

    swisskenny Funster

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    Apologies for resurrecting an old thread but I'm looking at getting solar for my motorhome and get more confused the more I read. How many batteries, how many panels etc etc? I am new to this after all!! I have 1 x 120Ah leisure battery and was thinking of buying this but would appreciate someone's advice who knows what they are talking about! :D Will be used in the UK mainly and I don't have EHU where I store the motorhome so I'd like to know my battery (batteries!) is/are getting a charge when stored and also that I can go "wild" for a few days sometimes without having to worry.Thanks in advance.

    http://www.ebay.co.uk/itm/100W-sola...472718?hash=item43cd42240e:g:-RMAAOSwEeFU-fD0
     
  13. mitzimad

    mitzimad Funster

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    if you want it to charge both leisure and vehicle batteried youll need a dual output regulator or a battery minder
     
  14. TheCaller

    TheCaller Funster

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    As mitzimad says, if the objective is to keep both the leisure & the starter battery topped up while in storage, then you need a regulator/controller with dual outputs or a battery master, which will top up the starter battery from the leisure battery. The kit you linked to won't charge the starter battery without the addition of a battery master. You can get one from Jim's shop on here.

    Whether 100W with a PWM controller will be enough when you are using the van will depend on whether or not you use it in the winter & what 12v equipment you use while you are away. You won't get a lot of output in winter in Scotland from that kit - probably just enough to stop the alarm draining the battery while in storage.
     
  15. swisskenny

    swisskenny Funster

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    Thanks for the replies - I'll re-evaluate my needs and look for something that can charge both the leisure and vehicle batteries and generate more power.
     
  16. chaser

    chaser Funster

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    Can anyone tell me without having to trawl through loads of posts , what is an mppt controler and how is it different from the other sort, thanks.
    I have a small panel now with a bog standard Chinese box but getting a larger one , do I need another controller.
     
  17. TheCaller

    TheCaller Funster

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    @chaser In very crude terms:-
    PWM controller. Traditional type; cheaper. The solar panel puts out a higher voltage than the battery needs. The controller chucks away the excess.
    MPPT controller. Newer development. More expensive, but converts most of that extra voltage into usable current at the voltage the panel needs. When connected to multiple panels wired in series, can also start charging at lower light levels than a PWM controller (& keep charging later into the evening & when cloudy).

    As I say, a very crude summary which may make the purists throw up their hands, but probably a fair summary for practical purposes.

    Can't answer your second question without knowing the rating of your new panel and the maximum output your current controller is rated for. You will almost certainly harvest more power from your new panel with a new controller, but whether that will be justified by the extra expense is another matter. If you have room on the roof, sometimes it's cheaper to add more panels or a bigger panel than to spend money on a fancy controller to extract the maximum from a smaller panel.
     
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