Solar Panel Voltage drop

Discussion in 'General Electronics Chat' started by afaik, Nov 13, 2008.

  1. afaik

    Thread Starter Member

    Nov 2, 2008
    I'm playing around with a pretty cheap solar panel. When I measure its output, its in the range of 15 or so volts. When I connect a load to it, it decreases significantly. For example, an led used without a resistor drops the Voltage output to 1.8V. A 1k resistor down to 1V. Why is there such a drastic drop and can it be avoided?
  2. bertus


    Apr 5, 2008
  3. Audioguru


    Dec 20, 2007
    Of course a red LED drops the voltage to 1.8V. The LED has a forward voltage of 1.8V.

    1V/1k creates a current of only 1mA which is extremely low for a solar panel unless it is not directly in sunlight.
  4. steveb

    Senior Member

    Jul 3, 2008
    Solar cells make very bad voltage sources. I find it easier to think of a solar cell as current source, much like a photodiode. However, I'm told that even this is inaccurate since they are not great current sources either. You need some type of regulator to convert this to a good voltage source. I'm sure this has been worked out by someone, but it looks like a challenging feedback problem, especially if your only power source for the regulator is the solar cell itself.
  5. afaik

    Thread Starter Member

    Nov 2, 2008
    I'm probably not understanding something very basic here, but why is it when I connect an LED to my power supply and set it to 15 volts, the LED would burn out, but in the solar panel case, it drops the solar panel output voltage. I'm sorry it's probably such a simple question. I've been studying electronics for about a year now, but sometimes we move so quickly that we don't have time to absorb long enough the foundational basics.
  6. beenthere

    Retired Moderator

    Apr 20, 2004
    It is a matter of current. An LED junction requires a certain voltage to put it into conduction. At that point, the LED will conduct and burn out due to heat unless current is limited by some device like a resistor.

    Your solar panel can't supply enough current to fry the LED - your power supply can. Most LED's get hot and die when more than 20 ma goes through them.