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Larry NK7E

Sunlinq 12 Watt Folding Solar Panel

Written July 08, 2007

Scotty, I need more power!

I bought the Global Solar Sunlinq SP-12 panel from Alternative Energy in July 2005 for use with my Yaesu FT-817 QRP transceiver. I have modified the FT-817 to roughly double the battery charging current since it took forever to charge modern cells, but doing this raised the current required to simultaneously run the receiver and charge the battery to 750mA at a minimum of 12V (9W). Regardless of the specs, the panel I received was not quite able to do this in the field. Here in Arizona we get plenty of sun, but solar panels are black and they get hot as asphalt in no time. Heat makes the cells "leaky" and the efficiency plummets like a stone. I was only getting about 6.5 Watts at 12 Volts and over 120 Degrees F on the panel surface.

Luckily, I live in Tucson where Global Solar is located, so I called their Customer Service to ask about what I should realistically expect from the panel. They told me there is a fairly wide variation in the output of individual panels. The numbers they give in the datasheet are "typical" and there is no minimum spec. However, I did get to talk to the guys in Engineering and they were very helpful. They tested my panel and agreed that it was toward the low end and they hand-picked a better panel for me. The new panel still couldn't quite make the 9W spot in the Arizona summer sun and I noticed the panel was generating wideband RF noise when it was illuminated. Further discussion with Engineering revealed that they used a 7815-style 3 pin voltage regulator to limit the output, but there were no filter capacitors. A 7815 driving a remote load this way will oscillate. They also have a 2 Volt drop from input to output. A design improvement was obvious.

The guys in Engineering gave me another plastic cover for the regulator board and I pried off the old one. I replaced the 7815 with an LM2940-15 low-dropout regulator, added capacitors to the input and output, snapped the new cover over the board and took it outside to try with the FT-817. The panel hit 750ma @ 12v even with the ambient temperature over 100 Degrees and no RF noise! Mission Accomplished.

I really like these little solar panels. In the past I have used both rigid and bendable panels, and they are a pain to carry. The Sunlinq folds up into a flat envelope that slides into the pouch right under the FT-817 and makes the coolest portable rig for camping. The only caveat is to be skeptical of the specs for any manufacturer's solar panel, as most datasheets seem to be full of wishful thinking by the Marketing Department. I have no doubt Global Solar could find a stock panel that when lit brightly enough and kept cool enough would produce the curve they show, but it ain't gonna happen on Field Day baby. Its an interesting exercise to draw in the 12W load line on the datasheet I-V curve. Also, remember my panel was one of the early production models. Current models may not have the issues I ran into.

Here are some numbers from my modified panel:

Date: 22 June 2007 1200 MST
Sky: Clear
Ambient Air Temperature: 100 DegF (actual panel temperature unknown)
Collecting Area of Cells: 3.75"x7.0"x8cells = 210 inches*2 = 1.46 sqft
Solar Intensity: 950 W/M*2 or 88.3 W/Ft*2 (from an Eppley Normal Incidence Pyrheliometer at The University of Arizona in Tucson.)
Incident Power: 129W
Max Power Out: 9.0W
Max Efficiency at Ambient Conditions: 7.0%
Open Circuit Voltage: 15.0V
230mA @ 14.5V (3.3W)
360mA @ 14.3V (5.1W)
620mA @ 13.9V (8.6W)
680mA @ 13.3V (9.0W)
750mA @ 12.0V (9.0W)
800mA @ 11.0V (8.8W)
940mA @ 1.7V (1.6W)


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