A few weeks ago I was reading a guest post over at QRPer in which the writer observed that his solar panels’ output was noticeably less than expected. This was perfectly in line with my own observations in the past, but if I ever tried to quantify it the data has been lost, and I decided to run some quick tests. I extracted my panels from the closet (some PowerFilm rollable panels I bought at Dayton some years ago), looked in the parts drawers in the basement and found some low-ohm power resistors for loads, and … waited for a sunny day.
The last item was the hard part; the last few weeks have been pretty solidly overcast, but about 11 am today the sun came out unexpectedly, and it was time to move this project forward! After working through a variety of hiccups like a solar panel that had developed a short circuit, a defective alligator-clip lead, and two (!) DMMs with blown fuses in the current-shunt circuit, I finally got some actual numbers.
In the weak and watery sunlight of mid-January the four panels produced 19 to 20 volts under no load, and when loaded with 50 ohms produced 13.37 volts, which works out to 267 milliamps. A bit more than 3.5 watts, is that right? This is not a lot, even compared to the modest requirements of QRP rigs.
I will work up a better test setup and do the same tests again later in the year to fill out the picture, but for right now I am not too confident in these panels for helping to keep my batteries charged on a long activation. I also now know that I need to buy a few of those expensive special fuses for the input of my digital multimeters!
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