Interpret data from Solar Panel tests...

Discussion in 'The Projects Forum' started by Cape_WP15, May 20, 2016.

  1. Cape_WP15

    Thread Starter New Member

    May 20, 2016
    Hello All, …total beginner here.

    I am trying to learn about solar panels in preparation for a couple of simple (I think) projects with solar powered fans.

    I have acquired an old EICO Model 1100 resistance box with which I have tested the two PV panels throughout the entire resistance range. I’ve compiled a data set and plotted the numbers. I am including two shared Google sheets with test results …hope the forum allows these links.

    My solar panels are from:

    1) A Nicro solar ventilator fan:

    2) A portable solar phone charger (with a USB output plug):

    My goal right now is to be sure I can interpret the test values in the right way. If I get this accomplished, I will go forward with the next steps of the project.

    The Nicro test results (in sunlight) are the most confusing to me. It seems that the numbers indicate the maximum output of about .2 Watts and .12 Amps at around 1.8v.

    On the one hand, this just seems like such small numbers! OTOH, this PV cell was originally supposed to spin a tiny fan motor (which can spin up with only 30mAmp), and to direct excess current into recharging a 1.2v 2000mAh NiCad battery that requires 200mA to get recharged (over 14-16hrs). So, then, with .12Ams > 230mAmps, it looks like the Nicro PV cell does have the appropriate output. I don’t know, …I just don’t have enough experience to be sure I am interpreting all the data correctly.

    On the USB charger, the maximum power of 1.15W and current of .22 Amps seems so far off the advertised max output of 5 watts and 1 amp. But the max volts of 7v are above the advertised 5v. Again, I am just not sure I am interpreting everything correctly.

    Please help me make sense!

  2. ronv

    AAC Fanatic!

    Nov 12, 2008
    It could be right. Panels are often spec'ed for 12 o'clock in the middle of the Sahara desert.
    Measure it on a really bright sunny day around noon.
  3. wayneh


    Sep 9, 2010
    Those are odd curves. You should show the data points you actually measured and not use Excel curve fitting, because I think it is adding artifacts.

    The current should uniformly increase as the resistive load is increased (lower ohms) and the voltage drops. It will nearly plateau once the voltage drops to ~0.7 of the open-circuit voltage, but it will never drop again as it approaches the y-axis (zero volts).

    When I've run these tests I usually go up in resistance and then back down, or vice versa. Point is, if the results of the duplicate measurements are not very close, then you know the lighting has changed.
  4. Cape_WP15

    Thread Starter New Member

    May 20, 2016
    Thank you for the replies!

    I re-ran the test (going up, then down with the resistance), but only had halogen lighting (evening). I was interested in how the curves would behave when compared with the same test in sunlight. See for yourself here (and scroll down for the last two tests):

    From what I can understand, over the course of the three tests, the output curve is similar along most of the resistance range (if you move beyond the very small Ohm values under halogen lighting).

    The Watt and Amp values are small, but look to be above the minimum load requirements of 30mA for the motor and 200mA for the backup battery charging. The motor needs at least 1.5V and in sunlight, the PV output is above that level.

    Am I reading and interpreting the test results correctly ?
  5. KeepItSimpleStupid

    Distinguished Member

    Mar 4, 2014
    Are you actually reading the voltage across the panel and the (voltage across your resistor) to get current?

    What's generally done is to "normalize" the cell so you would use J instead of I e.g Amps/sqcm. You might not need that.

    Light intensity is proportional to Jsc or the current at 0 volts. The standard is called AM 1.5 Global and 100 mw/sqcm. The AM is (Air Mass).
    So, yep noon on a sunny day might come close.

    There are a few points of interest.
    Jsc or short circuit current (V=0)
    Voc or open circuit voltage (J=0)
    Max power point. I can go into detail. MPPT
    Rseries - Usually a far forward bias resistance value
    Rshunt - Usually a reverse bias resistance value; usually expressed as a conductance
    FF Fill factor which is a "quality factor" expressed in %. 100% is not obtainable. It's the ratio of areas containing the MPPT and the one formed by Jsc and Voc. and the voltage axis.
    Efficiency = can only be known if the spectrum and intensity are known.
  6. wayneh


    Sep 9, 2010
    It would be nice if you had some resistor load values below 15Ω, since it appears that your maximum power for the one panel might be at a lower load resistance.

    At the least, you should see what the "short circuit" current is. You can just put the leads of the panel in parallel with the leads of your ammeter. Be sure the ammeter is configured properly for measuring current in the proper scale. Start with the 10A range if you're not sure.
    Roderick Young likes this.