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Solar panel/led

Discussion in 'Electronic Basics' started by [email protected], Mar 22, 2007.

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  1. Guest

    Can anyone tell me if it's possible to power leds directly from a
    solar panel? I need the light there and then, and not later on via
    batteries. Hope this makes sense. Thanks for any advice
  2. Bob Myers

    Bob Myers Guest

    Sure it is. Now if you don't find that answer, by itself, particularly
    helpful, you may want to stop and think about what additional
    information you might have wanted to include in your question...

    Bob M.
  3. Guest

    Keeping it simple, I want a "shed light" that operates during the day.
    They seem to consist of a 12v led spotlight and a 5 watt solar panel
    but most I've seen for sale don't have detailed specs. These would be
    fine except I don't want to store the power
  4. Rich Grise

    Rich Grise Guest

    Well, this question might seem somewhat off-the-wall, but, just to
    satisfy my curiosity, why do you need lights when the sun is shining?

  5. Aren't you really confusing things? I don't know what "shed lights" are,
    but the reason those garden LED lights have rechargeable batteries is because
    the sun is out in the day, but you don't need the light then. At night, you
    want the light, but there is no sun to power the LEDs.

    So you use the sun in the daytime to charge up the batteries, so the power
    will be available when the sun isn't.

  6. If you only need the light in the daytime, wouldn't a small skylight or
    window give you a lot more light for no more money?
  7. Bob Masta

    Bob Masta Guest

    Sounds like your shed is as dingy inside as mine!
    Others have suggested a skylight, but that assumes
    that one skylight will give enough light, where you
    need it. The LED approach allows the possibility that
    you can move it around to different areas as needed.

    The advantage of having the battery is not just at night.
    Since the sun comes and goes behind clouds, the LED
    brightness would fluctuate without a battery reservoir.

    LED brightness is controlled by the current through them,
    while the voltage across the LED is nearly constant. Without
    some sort of current limiter, a tiny increase in voltage could
    cause a whopping big increase in current and blow the LED.

    So normally the LED is driven through a resistor or a special
    current supply... almost *never* straight from a voltage source,
    unless it is something with an intrinsic current limit. Your
    solar cells may or may not fall into that category. My guess
    is that you can probably come up with such a system, but
    you might have to test a bunch of cells and LEDs first.

    So, it's probably simplest to use the resistor or current
    limiter right from the start. Personally, it seems simpler
    (and probably no more expensive when all is said and
    done) to use the ready-made battery system. They've
    probably optimized it and gotten the prices down via
    mass production in offshore plants... you will have to
    pay more for the parts, even if you work for free.

    Just a thought...

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    Scope, Spectrum, Spectrogram, Signal Generator
    Science with your sound card!
  8. jasen

    jasen Guest

    air, glass, and mirrors conduct sunligt a whole lot better than silicon and
    copper. for light during the day some sort of window, skylight, or
    light-pipe will be much more efficient than a solar-powered LED.

    I don't think you'll find a 5W panel on those cheepie garden lights:
    more like 0.05W
  9. Guest

    Thanks to everyone for the info. Sorry for the delay in replying.
    Bob has it about right. The ability to use the light in specific small
    areas is what I'm after.
    I agree the standard battery system would be cheaper but presumably it
    can't be charging and discharging at the same time, so it would tend
    to deliver light only later in the day.
  10. Bob Masta

    Bob Masta Guest

    I haven't actually used one of these battery systems, but I'd expect
    that there should be no problem with charge and discharge. In the
    morning, the battery will still be charged up from the prior
    afternoon. In principle you could have a *much* brighter light
    running from the battery, since it can charge over many hours
    at low current input from the solar panel, then put out a much
    bigger current for the short time you need it.

    Best regards,

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    Scope, Spectrum, Spectrogram, Signal Generator
    Science with your sound card!
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