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DIY solar power system

  1. Jun 24, 2017 #1
    Hello, I've been building my own solar panel system and throughout this process I've accumulated a lot of questions. If anyone could help answer them I would greatly appreciate it!

    First I'll start off explaining what I have.
    A polycrystalline solar panel 17V 2.2A and a mono crystalline panel 4.8V 4A (read by multimeter) I connect them in parallel to produce 16.8V 6.2A. Each of them have a "6A axial type" diode connecting the positive line and the solar cells.(I read that you use them to stop power from returning into the solar panels)
    I've connected them to a Shunt (which reads 12.9V 1.96A coming from the solar panels) and charge controller using a little less than 50 Ft of 10 gauge stranded copper wires. The charge controller is connected to a 12V 35ah battery that's connected in parallel to a 12V 7ah battery. I have an inverter that I connect to the load of the charge controller. I use that to power lights or charge cell phones.


    So that's my basic setup. As for my questions, I apologize if they seem a bit random and the large amount of questions I have.

    -Why is the shunt displaying 12.9V 1.96A if my multimeter is reading 16.8V 6.2A?

    -I bought 10 monocrystalline solar cells (4.8w) and connected them using adhesive copper tape but they produce less than my (2.8w) mono solar panel I built. I had soldered the solar panels up until I discovered copper tape. So does copper tape hold less lots and amps?

    -When I tried to connect my 4.8 W monocrystalline solar panel to my regular setup in parallel, it seemed like it actually took away from the power everything was producing, I don't know why.

    -Are these diodes actually needed if I have a charge controller?
    -Are they just taking away from the power the solar panels produce?

    -I decided I wanted to try powering small devices somehow and I found DC to DC converters. But I have no idea how to control the volts and amps enough so that it won't damage the electronics. I'm trying to power things like a peltier and a small fan. Can anyone help me understand how I can use the power I get to power these electronics?

    That's all I'll ask for now... it would be easier if I could upload pictures from my iPad or phone but I couldn't figure out how. I apologize in advance for any information I am missing and thank you for reading all of it.
     
  2. jcsd
  3. Jun 24, 2017 #2

    Averagesupernova

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    A schematic would be helpful. Connecting the solar panels with different voltages in parallel as you have makes no sense. If it weren't for the diodes the higher voltage cell would simply feed into the lower. With the diodes, only the higher voltage cell is sourcing any current. How did you arrive at 16.8 volts?
     
    Last edited: Jun 24, 2017
  4. Jun 24, 2017 #3
    I suppose that would help, I've never made a schematic before but I will try to make one and upload it.
    Thank you
     
  5. Jun 24, 2017 #4

    davenn

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    because the open circuit voltage of the panels is always higher than when loaded

    without knowing the details of how you hooked them up ... who knows ???

    only if there are separate inputs to the controller


    well there will be around a 0.7V drop across each diode

    I have to repeat what Averagesupernova said .....

    you SHOULD NOT be connecting different value voltage sources together


    Dave
     
    Last edited: Jun 25, 2017
  6. Jun 25, 2017 #5
    Thank you for replying, the monocrystaline solar panels connected with copper tape are connected in series.

    Why should I not connect the solar panels like I have them? It doesn't seem like they are being damaged but I am curious as to why you say that.
    Also I am working on completing that schematic to give a clear understanding of my setup.
     
  7. Jun 25, 2017 #6

    davenn

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    it doesn't matter if it is solar panels, batteries or other type of power sources .... you don't connect ones that are not the same voltage
     
  8. Jun 25, 2017 #7
    If you use diodes to prevent reverse current going into the panels, it will be safe, but the 4.8V solar panel can only produce current if the overall output is 4.8V or lower, so you have to use a low resistance load to get this panel to contribute. At this output voltage, most of the power that the 17.2 V panel produces is thrown away.
     
  9. Jun 25, 2017 #8
    I don't quite understand, it seems as though the (17V 2.2A) panel is unaffected and the (4.8V 4A) panel is just contributing amperage. They're feeding into a charge controller that's feeding into a deep cycle battery. Is there a more efficient way of going about this?
     
  10. Jun 25, 2017 #9

    berkeman

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    The schematic really is needed before we go much further. What you have posted above makes no sense (unless I missed a place where you corrected it).
     
  11. Jun 26, 2017 #10
    IMG_0311.PNG
    I finished making the schematic and I apologize for how crude it is, its my first time ever making one. If there is any information I left out again I apologize.
    I'm apparently terrible with computers too... but I'm trying to learn how to work with them.
     
    Last edited: Jun 26, 2017
  12. Jun 26, 2017 #11
    So if I wanted to fix the problem of connecting a 17V and a 4.8V panel, would the solution be to connect DC to DC Converters?
    I've looked on amazon and it seems like the problem is those converters can step up the voltage into the 30s but the amperage it can handle is too low (near 2-3 amps). The ones that look like they can handle the power my solar panels are producing are like $30. Also I've never bought a transformer or converter before.
     
  13. Jun 26, 2017 #12
    Thanks for the drawing.

    Another issue involves different amp-hour rated batteries wired in parallel (generally accepted practice is they should be identically rated). Even if they are identically rated, a shorted cell in one battery requires the good battery to discharge into the faulty battery, leading to it overheating and to possibly explode. This potential failure mode ought to be considered in the design.
     
    Last edited: Jun 26, 2017
  14. Jun 26, 2017 #13

    berkeman

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    No need to apologize -- you are learning by doing, and working with solar energy systems, which is all great. :smile:

    This has probably already been mentioned in the thread, but keep these things in mind:

    • Stiff voltage sources like batteries need to be rated at the same output voltage before you can hook them in parallel
    • PV panels are medium-stiff voltage sources, so you need to only connect them in parallel if they have the same output voltage rating at the same input insolation
    • You can parallel-connect different PV panels of the same output voltage even if they are rated at different output currents at that output voltage for the same insolation
    • You can series connect PV panels that are rated at different output voltages but the same output currents given the same insolation
    • There is typically a Maximum Power Point (MPP) for a PV panel output, where it is producing the most output power for a given insolation. Good PV power converters will help the PV to work at that MPP (a tradeoff between the PV panel's output voltage and current).
    • Differently built and rated PV panels may have different MPPs, so it's generally a bad idea to mix and match if you want to build an optimum system

    Hope that helps.
     
    Last edited: Jun 28, 2017
  15. Jun 26, 2017 #14

    Averagesupernova

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  16. Jun 26, 2017 #15

    Averagesupernova

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    @Brandon91man Move your shunt around. Place it in series with each PV panel individually and you will see why paralleling your two particular panels is not doing what you think it is.
     
  17. Jun 27, 2017 #16
    @Averagesupernova
    Thanks to the both of you, I will try moving the shunt around and see what I find. Although this is the first time I've used a shunt and I didn't know you could connect it in different ways.
    And @berkeman I didn't know mixing different solar panels was a bad idea. So that's good to know. I really was hoping that would be an easy fix with DC To DC converters though.

    @Asymptotic

    Thank you, That is useful information to know.
     
  18. Jun 27, 2017 #17

    berkeman

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    The right solution for mixing panels or panel configurations is really to have a MPP power converter for each contributor panel configuration that can't be easily put in series or parallel with another panel configuration. The output power of the multiple MPP power converters would then be combined in some way, typically after synchronized inverters. That's a fun project to build, but at your level of learning so far, you would need to find packaged inverters that could be synchronized, and buy a couple MPP power converters.

    What-all do you want to power? Maybe you could just have two separate PV powered systems that are independent?
     
  19. Jun 27, 2017 #18

    Averagesupernova

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    There really is only one way to hook a shunt. It goes in series with the current you are trying measure. Don't hook it across a voltage source.
     
  20. Jun 27, 2017 #19
    Well, for now I'm powering tablets and lights. My ultimate goal is to setup a grid tied system, but I also want to use them in projects and electronics too. For example, I want to eventually get to the point where I can build an electronic system that will use solar power to charge a battery that powers a peltier A/C system (still researching that) and that peltier A/C only turns on at a specific time of the day.

    My desires require me to learn and understand thermodynamics, electronics, solar power, power loss, power used, and probably much more. I'm actually extremely happy I found this forum. I didn't even know my panels were connected incorrectly until the other day.

    (I know that's more than what you asked for but I feel like there are a lot of brilliant minds here that can help me get to where I want to be)
     
    Last edited by a moderator: Jun 28, 2017
  21. Jun 28, 2017 #20

    berkeman

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    One thing to learn early when you are considering building a grid-tied system, is that your local electrical utility will have regulations for how you make that tie. There is special equipment needed (and the utility has to inspect it and sign off on it before you can make the grid connection). One of the biggest reasons is that if the grid de-energizes for some reason (like a breaker blows at your street's distribution transformer), the utility needs you to stop pushing your power back toward the grid. This is to keep repair people from getting electrocuted by what they think are de-energized powerlines on your street.

    This is called Anti-Islanding protection:

    https://solectria.com/blog/anti-islanding-protection-with-grid-tied-pv-inverters/
     
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