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DIY Solar Panel

Discussion in 'General Electronics Discussion' started by quantumtangles, Dec 24, 2012.

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  1. quantumtangles

    quantumtangles

    152
    3
    Dec 19, 2012
    What is it?

    DIY solar panel made from 4 x 3.8w mono-crystalline solar cells. Poly-crystalline cells are fine though they have a lower energy density (your panels will be larger for the same power output).

    What does it do?

    Tested in direct sunlight on 3rd December 2012
    2.34 volts @ 5.00amps = 11.7 watts
    (high energy density solar cells).

    How do you make it?

    Each solar cell is wafer thin. No matter how careful you are, you will break some of the solar cells when building large solar panels. It is a good idea to make a test piece from the ones you break, or from overheated cells warped by your soldering iron.

    In terms of polarity, solar cells are just like the silver oxide batteries you get in quartz watches. One side is negative and the other positive. Counter-intuitively, the top side of each solar cell (the dark side that faces the sun) is negative. Tabbing wire (thin pre-tinned wire) is soldered to the fairly obvious white lines in the middle of this side of the cell.

    The underside is positive and has two or three little lines to solder the tabbing wire to.

    Once you have soldered half of a double length of tabbing wire to the back of a solar cell, you then take the extra 50% length of the same tabbing wire and solder it to the front (to the dark side or sunny side up side) of the following solar cell. So you end up with the solar cells joined together just as if they were silver oxide batteries in series, stacked one on top of the other, positive to negative and so on.

    So you joined two solar cells together by taking a piece of tabbing wire twice the length of the cells. You joined the base of the first cell (cell X) to the top of the second cell (cell Y). To continue the string, join the base of cell Y to the top of a third solar cell (cell Z) and so on. The bus wire is thicker tabbing wire capable of a higher power rating. You use the wider bus wire to ensure you end up with only two terminals (one positive and one negative) regardless of how many cells you add together in series.

    The voltage from each solar cell is quite low (it may be about 0.5 volts per solar cell). But when you add them together in series (for example, in a 36 cell '9x4' configuration....as in most commercially made solar panels) the voltage will stack and give you approximately 20 to 22 volts (actual voltage always depends on the light in lumens per square metre or lux hitting the panel), whereas the current will remain at about 5-6 amps (the same as it is for only one solar cell, though again light dependent) because, in series, you have only stacked voltage and not current.

    This 20 to 22 volts (in strong direct sunlight) is the voltage one would expect from a so called '12 volt' solar panel.

    If you string 36 of these cells together in series (making up a single solar panel), you will get approximately 137.5 watts per solar panel in strong direct sunlight.

    Bill of Parts for Redneck Solar Panel

    4 x 3.8w Mono Solar cells (I used broken solar cells for this test piece...and any solar cells will do)
    Tabbing wire x 1m
    Bus wire x 0.5m
    Rosin flux
    Solder
    Flat nosed soldering iron
    Reverse current protection diode*
    Hard level surface (for soldering tabbing wire to wafer thin solar cells)
    Hot Glue Gun
    Twin and Earth Cable (any colour strand) 1m
    Frame and glass from an annoying painting or picture someone gave you for Christmas

    *Chunky Diode (the one in your parts bin that looks too big for anything else). A Schottky diode will do the same job as a Zener but has a lower voltage drop.

    Serious (non-delirious) panels?

    For serious (9 x 4 cell) long life panels, use DOW SYL resin or viable alternatives to prevent oxidation of solar cells and to prevent condensation. Most resins react to UV light and become opaque or milky after a few months and should be avoided. Try and use tempered glass for the front of the panels as well. Ordinary glass may shatter in a hail storm and perspex will probably become opaque or discolor after a few months. Also, you must 'diode protect' the solar panel output terminals to prevent damage.

    Solar cells are falling in price, however, the tempered glass, DOW SYL resin, aluminium frames and solar junction connections (including a diode) that you will need to protect DIY solar panels are expensive. It makes economic sense to buy commercially available panels rather than make your own unless you can get resin and aluminium frames cheaply.


    But if you are making a test piece (especially from broken solar cells), you can do anything you like :D
     

    Attached Files:

    Last edited: Dec 24, 2012
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