Summer Solstice PV Test

[Rock]

So it's the summer solstice here at 41.2 degrees north. Yesterday was mostly sunny with typical Midwest fluffy white clouds moving past at a pretty good clip.

I have the Harbor Freight 45 watt solar "kit" which contains 3 panels presumably rated at 15 watts/piece. So I got one of the panels out to play with.

Right around "high noon" (actually about 1:20 PM I think in my locale DST) I measured about 24 volts open circuit. I think this is about expected. Next I hooked up the one panel to a car battery that had been used to run my Engel for several hours. The battery read about 12.55 volts open circuit without the solar cell attached.

Tilting the panel as best I could for maximum output, it seems that steady state max current with this setup was about .95 amps. I saw peaks up to almost 1.1 amps as the clouds would move out, but these were short lived so I wonder if it was just a meter response issue or something else. The battery voltage was around 12.65 when charging.

So if we do the math (.95 X 12.65) we get right at 12 watts. So pretty good for cheap HF hardware, but still 20% less than rated. I guess I have to go to the equator or at least Arizona to hit that.

Some observations. I was close to being under the overhead power feed from house to barn. When the wind would blow the cable to where it came over the panel it would cast a say 1/2" wide shadow the length of the panel. This would drop the output to the .85 range (no cloud cover.) As others have noted here it doesn't take much shadow to make a difference. Also, when the white fluffy clouds would move over the panel, output dropped more than 2/3ds, to the .3 amp range. So they'll charge the battery on a cloudy day, but not much.

The panel was still hooked up when I got home late, and I measured no current draw in the dark, so this means each panel has a blocking diode built in, which is good.

I need to do some average amp and duty cycle draws on the Engel in typical usage. This test shows that I need more solar capacity if I was to consider boondocking for a week say (which is not currently on the schedule, but hey.) I have a HF coupon for the same 45 watt kit for $180. They also Emailed my a 20% off coupon. If they let me use both, that's $144. According to the book they shouldn't, but I'll see what I can do.

Using real rough estimates, with 90 watts of rated HF solar cells, under ideal conditions I would need only 2.5 hours of full sunlight to run the Engel for a day. So give me 8 hours of mixed/random conditions (location/usage dependant) and I should be OK.

Eric

[ARKPAT]

Thanks for the information on the panel. Yes shading does effect solar panels; some more than others. I hope to get some of my system up and working. I have a 43 watt Kyocera panel and HF solar charger / jump start batteries.




Pat