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Solar panel/Wind generator test load

Discussion in 'Renewable Energy' started by JMW, Jan 29, 2016.

  1. JMW

    JMW Member

    Nov 21, 2011
    Puerto Rico
    I was working on a boat with two 75 watt solar panels. The owner was unsure whether or not they were developing rated power. He was using a charge controller and approximately 2.5 amps were being driven into the batteries. I needed a load that would test the output of the two panels. They were 12 volt panels developing 19 volts open circuit...........what to do?
    Back in the old days we would test the ships main generators by using a saltwater test. Basically a large tank with electrodes and filled with sea water. (We made a great deal of caustic soda). I used two pieces of copper tubing immersed in a vinegar solution. I made the tubes with adjustable distances to vary the resistance. A fully charged Ryoby battery provided the "calibration" voltage.
    Cheap, quick and effective, who could ask for more? As H2 is generated and coats the electrode increasing the resistance, you must reversed the connections periodically. (LEO the lion says GER)
  2. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

    Apr 17, 2007
    Loveland, CO USA
    When I worked with larger systems I used car headlights for a load.
    If you are in the 2.5A range then use smaller lights.
    I made a wall of sockets and just screwed in the number of lights needed to keep the panel loaded.
    You don't want to put 19V on a bulb, but with some bulbs in place the voltage will be below 15V and that should be fine.
    • Like Like x 1
  3. cowboybob

    cowboybob Well-Known Member Most Helpful Member

    Oct 22, 2011
    James Island, SC
    Google "100W resistor". A bunch show up. Even Walmart has one! Don't know what will be easiest to get in PR. Buy two of them.

    Set up the panels, if possible, so that you can test their output at full sun with the panel straight on to it. Then angle it off at 45°s and check the output again. Crude, but it'll give you a less than optimum output for comparison.

    Monitor the voltage across the just one resistor as the load and, of course the current through it. Do the same again with both resistors in parallel (and the in series, if you like). We're just varying the load in an attempt to get near 13.5VDC optimum charging voltage). Use the resistor arrangement that best meets that goal for your tests.

    Understand, of course, that the panel manufacturers rate their products at a perfect, noon, straight-on time. And a sea level, output is at it's least (compared to 5,000 feet, for instance).

    Let the owner know just how much the panel(s) output varies through the day and with alignment. At best you can only demonstrate a crude average. Probably close to the 2.5A your seeing now (approx. 30W)
  4. dave

    Dave New Member

    Jan 12, 1997

  5. MikeMl

    MikeMl Well-Known Member Most Helpful Member

    Mar 17, 2009
    AZ 86334

    2.5A into a 14V (during charge) battery is only 35W, so something is fishy... If the battery bank has not seen a load overnight, then there would be a short time in the morning where the solar charger would deliver a couple of A for a while to replace the surface charge that dissipated overnight.

    What happens if during bright sun, you just go around the boat and turn on all of the lighting, etc. Use the boat loads to determine the health of the panels...

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