Adding more panels

Discussion in 'Solar Power' started by HobbyHarvey, Mar 13, 2018.

  1. HobbyHarvey

    HobbyHarvey Funster

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    Hi all, we currently have a single 60 watt panel charging two Varta140Ah batteries, the panel more or less copes in sunny climes but We are looking to add either a single 150 watt or 2 X 100 watt panels along with a Victron smart mppt controller.
    We would appreciate any advice or suggestions on this as to best configuration and also advice on which size controller to go for.
    In simple terms please, as although I am practical, I am not too electrically experienced.
    Many thanks, Mike and Dana.
     
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  2. Urs4_2008

    Urs4_2008 Funster

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    Hi. Victron is a safe bet! Either exchange the setup you have for a 150w or 2 x 100w panels with a Victron MPPT 75/15 or just add the 75/15 (with the new panels in series) without changing the current setup (running both chargers in parallel).

    Do not connect old panel together with new panels in series or parallel if you do not know what you’re doing.
     
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  3. Richard and Ann

    Richard and Ann Funster

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    Whatever you buy, get a controller that also maintains the starter battery so you can have the radio on (y)

    I fitted a Votronic mppt 250 :cool:
     
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  4. funflair

    funflair Funster Life Member

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    I like Votronic as well, I second putting the new panels onto their own dedicated controller but I would go parallel rather than series, somebody posted a YouTube video yesterday that seemed to back that up and the "man from Votronic" told me to.

    Martin
     
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  5. Urs4_2008

    Urs4_2008 Funster

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    Serial: less cable loss due to higher voltage. More sensitive to shadows (don’t park under a tree). Parallel: more cable loss, shading one panel will only reduce that panels output.
     
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  6. funflair

    funflair Funster Life Member

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    OK thanks I understand the theory, I was careful with my three panels to keep each one on its own 4mm cable to minimise loss before going inside to 6 mm cable to the controller,

    IMG_E0348.jpg

    Martin
     
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  7. pappajohn

    pappajohn Funster Life Member

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    I really think any cable losses over such short distances aren't a concern.

    99% or more of those members with multiple panels will be wired in parallel and nobody has said "I must rewire my panels to series"
     
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  8. Urs4_2008

    Urs4_2008 Funster

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    You’re probably correct that nobody have stated that they need to rewire their solar to serial :) Not trying to rain on your parade here, rather enlighten the fellow funsters :)

    2 x 100w can produce 12 amps in optimal conditions connected in parallel. 12 amps at 17 volts (vmax on my panels) running ie 6 meters will generate an efficiency loss of 3,53%, which is above the recommended 3% max in 12 volt installations.

    Let’s say you want 400 Watts now, or in the near future, the same setup will result in a loss of 7% if connected in parallel. Running the panels in series will bring loss down to 1.75%

    Biggest issue when above 200 Watts and a “normal cable run” can be hot - and potential dangerous overheating of the cables.

    In my own experience in a normal motorhome with 400 Watts in parallel running awg11 and shortest cable run (in my case about 6m), the cables becomes too hot for comfort. In this parallel configuration one should probably go with awg7 or thicker cable - which few does because of cost and more difficult/invasive/destructive installation process

    Your own actual losses you will need to calculate using your own data from your panels, and your cable size and length.

    http://www.calculator.net/voltage-drop-calculator.html

    Hot cables can be bad, as well as high voltage shock. Be careful :)
     
    Last edited: Mar 13, 2018
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