I am working on a project where I need about 20 mA to come from a particular solar panel I am in possession of. The solar panel is an MP3-25 panel, I actually have 2 which I am trying to get to work. The panel is rated at about 25 mW, and I got it to output that much power, even indoors, for a few seconds. I was testing it continuously with a multimeter, and for some reason it put out about .21 mW instead of 20-25 mW the rest of the time. I wonder if something would need to be done to lower the voltage, as it is possible at a very high voltage the panel cannot output the proper current. I am right now unable to make it produce the proper amount of power, which is quite frustrating.

What steps can I take to get the solar panel functioning? I have tried making a good connection to it in several different ways, and I have brought it outside and it still only output about .66 mW in broad daylight.

Right now I am directly shorting the panel through a current meter, perhaps that is the issue. Is there some special way to measure the current? Solar panels are meant to output current near the current they would provide in a short circuit, so I doubt this is the issue but it could be.

  • \$\begingroup\$ You might want to inform yourself about mppt (maximum power point tracking) \$\endgroup\$
    – PlasmaHH
    Commented Mar 13, 2015 at 21:11
  • \$\begingroup\$ @PlasmaHH I've been reading up on the I-V curve for this panel, I'm trying to figure out a way to drop the voltage. I tried an LED, which sadly did not help. Also, the voltage my multiplier picks up is often about 2.5-3 volts, which is much below the voltage where current starts to fall drastically, so I'm not sure if this is the issue. \$\endgroup\$
    – user16871
    Commented Mar 13, 2015 at 21:15
  • \$\begingroup\$ For testing purposes a resistor will suffice, for real usage some kind of smps with variable input impedance will do, as I said, read about mppt. \$\endgroup\$
    – PlasmaHH
    Commented Mar 13, 2015 at 21:20
  • \$\begingroup\$ @PlasmaHH Alright, now I'm really confused. I have another solar panel which is larger and for a different project. It is supposed to output 200 at 4.5 volts, I am getting 0.2 mA at 2.5 volts in a well-lit area. \$\endgroup\$
    – user16871
    Commented Mar 13, 2015 at 22:05
  • \$\begingroup\$ Do not expect to get the rated value unless you're outdoors in strong sun. Also you're switching between amps and watts in your description. Try measuring the power into a potentiometer at various settings up to e.g a kilo-ohm. And are you sure about those sub-ma readings? \$\endgroup\$
    – pjc50
    Commented Mar 13, 2015 at 23:22

1 Answer 1


It is a little confusing since you jump from watts to amps and back and forth, but I believe that you do know the difference between the two.

I suspect that even though you are outside, you are not in the full sunlight that the panel requires. Broad daylight is not enough, it needs bright blistering sunlight.

Remember that a solar panel will output full voltage at light intensity levels as low as 10% of maximum, while amperage is linear. So 10% light level = approx 10% max amperage (for a given voltage)

You are correct, the short circuit amperage reading should be close to the actual current output.

Also, the smaller panels may not have bypass diodes and so even the smallest little speck of shade on one part of one solar cell will dramatically decrease amperage (I.e, your thumb provides a small amount of shade on the panel while doing the measurement and the amps will drop by 50% or more!)

If you want to map your own I-V curve, you just hook up a number of different resistors one at a time in series from the positive to the negative of the panel and measure the voltage drop across the resistor and using ohm's law calculate the current.

Good luck.


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