Help with solar panel - orderd scrap cells, have questions

Discussion in 'The Projects Forum' started by rudyauction8, Sep 28, 2014.

  1. rudyauction8

    Thread Starter Member

    Jan 27, 2012
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    I just ordered 70 watts of broken cells for about $10. My question is, if I use them to build a panel and some are smaller than others, will the panel be current limited by the smallest one, and will the smaller one be damaged? I plan to wire them in 30 series 2 parallel configuration, since I should be getting around 70-75 cells.
     
  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    If the pieces are all from single cells, ie, all are 1/2 V, then select pieces of approx. same size to be wired in series. Might parallel same size smaller pieces before adding them to series string. Remainder of small pieces can go in a series string of thier own. Strings should have nearly the same no. of cells; under load V will equalize.
     
  3. John A. Smith

    New Member

    Sep 28, 2014
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    From what I remember when I was playing with a Solar Panel project for my home. The size of the panel/cell will determine the ampere and how you connect them the voltage. Most solar cells put out about 0.5 volts.

    Not to squash your plan, but making any usable power will be difficult. Than you have to encase the cells. Regular soda lime glass will cost power, so you'd need "Low Iron" Tempered glass, plexi is not a good substitute as the transmittance of the light in the wavelengths your looking at is very low.

    I ordered some 0.5 v 3.5 cells and spent significant time soldering them, stringing, using the correct diode, encapsulating, framing, etc. etc. to have a panel that would barely put out 12v.

    Good luck, it' worth the experience.

    John

    Bernard,

    They don't technically balance, the array will only put out the amount of power of the lowest cell.
     
  4. rudyauction8

    Thread Starter Member

    Jan 27, 2012
    252
    2

    Thanks for clearing everything up. I have the enclosure figured out, and I figured the smallest cell would limit the panel, I just didn't know if it would be damaged. With 30 cells in series at 0.55v each I should have around 15 volts at around 3-4 amps, which is about right for charging deep cycle batteries when combined with my current panels.
     
  5. John A. Smith

    New Member

    Sep 28, 2014
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    The 15 volts and 3-4 amps are under perfect conditions. Solar cells make the most power when they are perpendicular (maybe +/-10%) in two axis to the light source. Any shading of the ONE of the cells will lower the output of the Panel. Than with any glass/plastic covering of the cells you'll lose 10% minimum due to absorption, reflected light, etc. etc. Just saying that so when you get the 15v at .5 amps you won't be disappointed anything greater will be like White Bread and Gravy ;).

    In my first go, I used Evergreen 5" x 3.5" new cells, strung 12, used a diode and 12 gauge wire (it turned out to be overkill), tempered soda lime glass and an aluminum frame with a Silicone Liquid (Dow product used to be an industry standard), so I got my 12 volts the amps when aligned in two axis was a whopping 2 amps. I'm not exactly none technical, I was the lead technician in the Micro Fiber Optic R&D for Corning Inc.
     
  6. rudyauction8

    Thread Starter Member

    Jan 27, 2012
    252
    2
    Well I have a large section of roof with unblocked sunlight from ~10am until ~4pm, my 20 watt panel generates about 17 watts during this period and generates about 10-15 watts in the early morning and late afternoon, so I'm pretty sure my needs of about 150 watt-hours per day will be met as long as the sun's out for at least a couple hours per day. Also I still get about 8 watts when cloudy.
     
  7. John A. Smith

    New Member

    Sep 28, 2014
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    What Charge Controller will you be using? A PWM or MPPT type?
     
  8. rudyauction8

    Thread Starter Member

    Jan 27, 2012
    252
    2
    I'm designing my own, PWM with 14 volt cutoff. I'm building my own because I have almost all of the needed parts already. I'm planning on making it handle up to 50 amps, and have multiple inputs so I can hook up wind turbines and more than one bank of solar panels. It'll be charging 2 car batteries, one RV battery and 2 electric scooter batteries all in parallel. I have a 350 watt and 400 watt inverter for AC power and am getting a 1500 watt inverter from a friend.

    Also when the batteries are full the controller will switch the power over to a small heater, as it's starting to get cold and I don't want any energy wasted.
     
  9. rudyauction8

    Thread Starter Member

    Jan 27, 2012
    252
    2
    Got my first panel up, it's generating about 1.4 amps average at 13 or so volts (16 volts open circuit), and I have enough cells left to build at least 4 more identical panels. I'll end up having much more power than I need.
     
  10. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    With 16 V OC, loading panel down to max power, operating V might fall as low as 12V. I would add another 2 or more cells to each string so panel can operate under more variable conditions.
     
  11. rudyauction8

    Thread Starter Member

    Jan 27, 2012
    252
    2
    I would have but I had no more room on the board I used as a frame. They seem to work quite well charging my batteries and have more than doubled my charging power.
     
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