24 Volt Solar Panel Wiring Build

ia_dreamia_dream Registered Users Posts: 1
I am in the process of wanting to build a 72 cell (6 x 6 Cells used)solar panel but am not sure of how the individual cells are to be connected on the panel itself.  I am modeling after another panel I have seen online which is 6 rows across and 12 rows tall.  Can anyone help me with this?  My email is [I would suggest sending via private message or post here--Deleted email address for poster's privacy. Note to poster, if you want your email address public, please feel free to edit this note. -Bill B. moderator] if you can send me a diagram to that email address I would really appreciate it.  Thanks in advance

Comments

  • PhotowhitPhotowhit Solar Expert Posts: 4,280 ✭✭✭✭
    edited September 2016 #2
    Each cell will put out about 1/2 volt, so for charging voltage for 12 volts you would want 2 parallel strings of 36 cells, for roughly a 18 volt vmp panel.

    Cells in each string would be wired + to - and the strings connect + to + and - to -.

    You might check for dead cells before starting and perhaps a small load check of some type to be sure the cells are viable. There are some reports of 2nds being sold as 1st quality cells.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • BB.BB. Super Moderators Posts: 26,872 admin
    To add to Photowhit's answer...

    More or less, every series string of 12 volts (~24 series cells) maximum should have a bypass diode. if there is one or more cells shaded, they go "high resistance" (do not pass current). You need a bypass diode to let the current around the shaded cell to prevent the shaded cell from being damaged/ruined by high voltage of the rest of the string.

    Next question--What Vmp voltage do you want from the panel. Nominally, you would have 36 cells in series for a Vmp~18 volt panel--Good for charging a 12 volt battery bank. If you are charging a 24 volt battery bank, you would want all 72 cells in series.

    For your panel--If you are doing 6x12 array... You would have 3x series string (24 cells in series) and a bypass diode per series string (3x bypass diodes in total). That would give you a Vmp~36 volt panel--Perfect for a PWM charge controller (the cheaper type) to charge a 24 volt lead acid battery bank. If you are going to have a 12 volt bank, or a lot of panel (more than 800 watts or so), then you would probably want a MPPT type solar charge controller (maximum power point tracking--The more expensive type of charge controller).

    Here are some interesting links on making  a nice solar panel:

    http://fieldlines.com/board/index.ph...,144982.0.html
    http://fieldlines.com/board/index.ph...,144995.0.html
    http://fieldlines.com/board/index.ph...,145004.0.html

    Now--The warnings...
    • large solar panels have enough current & voltage that they can cause fires. Solar panels should not be made from plastic or wood. They should be made from glass (ideally tempered glass) with non-flammable/flame rated materials).
    • many raw solar cells these days are rejects from solar panel mfg with defects. These defects can affect how well the panels will work, create hot spots in panels, and such.
    • new solar panels these days are running at less than $0.90 per watt. It is very difficult to build solar panels that will standup to heat and weather for less money (and as high of reliability).
    And, my one warning per thread that what you are doing does carry risks. Here is "gray market" solar panel (array) that caught fire on a house:

    http://forum.solar-electric.com/discussion/3375/panel-fire-question/p1

    Be very careful at about your material selection, mounting & electrical hardware, and where you will mount the array (not on your home's roof, not over dry brush, etc.).

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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