Solar Panel project -Help needed

Discussion in 'The Projects Forum' started by quaser, Oct 25, 2012.

  1. quaser

    Thread Starter New Member

    Sep 22, 2012
    7
    0
    Hello!!

    I want to build a solar panel to charge lead acid battery... and use the later to power 6 to 8 bright LEds through out the night...(or I might add motion trigger)
    I went through previous posts on relevant topic and this is what I summarized

    a 32 Watts Solar Panel approx 2.6 Amp at 12 V


    40 Ah lead acid battery ( 6V?)

    PIC uC for monitoring theprocess

    Is this ok? this is my first project in like years!! Please help me out!

    regards,

    quaser
     
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,394
    1,606
    A solar system is a balancing act between what your load needs, what the battery can supply, and what the panels can produce.

    Step one is to figure out your max load. How much current for how long will the LEDs draw? Multiply that to get the amp-hours required for the LEDs.

    Step two: pick a battery. You want no more then 50% capacity used each night, 25% is better to insure a long battery life.

    Step 3: PV Panels: A PV panel is a current device, meaning if you connect a 2.6 Amp at 12 V panel to a 6 volt battery the voltage will drop to the battery voltage, so you only get 2.6A x 6 volts = 15.6 watts out of it unless you get a sophisticated MPPT controller. Look it up, there are some cheapo units out there.

    The huge balance point is winter days where you get the least charge time but the longest load time. Figure 5 hours of daylight just to be safe. With your panel you're just getting 2.6A * 5 hours = 13 amp-hours to charge a 40 amp-hour battery, and that's 100% efficient.

    Having the PIC there can help, you can use a MOSFET switch to open the charge current when the battery is charged (over charging is a battery killer), or even make a controlled current input (PWM works well there).

    Also, the NEC has been specifying standards for this since 1985. You can find LOTS of non-compliant systems out there. Your system is simple and possible to make it close to code, but not if you make your own parts, they are not "listed devices."
     
  3. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,175
    397
    Start with load, LED color or Vf,& nominal operating current. Prob. White, about 3.3V @ 20 mA, 10,000 mcd; 100mA, 100,000 mcd; or 300 mA for 1W, give or take.
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,148
    3,058
    FWIW, you might want to study some commercial products that are very similar to what you describe. For instance the Westinghouse (International Dynamics) 482101MT 50-LED light string. It employs a 3.5" x 3.75" panel (just over 13 square inches) to charge a 1AH sealed lead acid 4V battery. It is advertised to light a string of 50 LEDs for 6 hours each night, automatically turning itself off to save the battery.

    It can't possibly drive all those LEDs at 20mA for 6 hours, but they're "bright enough".

    The circuitry, which I've posted in this forum, somehow controls things to properly light 3 to 50 LEDs (it comes with 50). It also uses a transistor to dump excess PV panel current once the battery reaches 5V.
     
  5. greenman

    New Member

    Oct 31, 2012
    1
    0
    Hi,

    I'm a bit of a newbie to this forum and came here to get some tips on solar panels and jeez, I knew it was technical but this is just mad! I'm barely able to follow... wish I listened in Physics class now. My father is associated with a few SMEs who are all considering going a bit greener and so I've been looking up at low-cost methods, in addition to some info I got some this site about solar panel installation but I'm pretty much in the dark here. They know nothing about solar energy and the logistics of it, and neither do I. ErnieM, your post was quite helpful for a beginner but it looks like I'm going to have to research each step! It's a good start though thank you, I'll be sure to keep you guys updates on what I do.

    Cheers!
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,148
    3,058
    Designing any power system, solar or otherwise, draws together a lot of different technologies. Physics, electronics, mechanics, economics and so on. Fortunately there are plenty of other folks working hard in the area, so read all you can stand.

    The link provided in the 2nd post in this thread is very useful and should be required reading for any newbie before they post here.

    One piece of advice I can give you is to clarify what your goals are. That will help you make other decisions on implementing your plan. Save money? You might as well stop now. Go green? How far - what percentage of your power do you want to come form solar? Have fun building something useful? Learning and experience? Go for it.
     
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