Solar Panel output in the shade? - Page 2 - Fiberglass RV


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Old 07-04-2013, 11:36 AM   #15
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Name: Norm and Ginny
Trailer: Scamp 16
Florida
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Ryan, I started doing some testing with our solar panel thay may help you.

I started with a fully charged battery on a partly cloudy day.

Our trailer has all LEDs.

I turned on one LED and the solar panel supplied 0.2 amps. I turned on 4 LEDs and the solar panel supplied 0.8 amps.

Since the battery started fully charged the solar panels only supplied replacement current, the amount used by the LEDs.

I tuRned off two LEDs and it dropped back to 0.4 amps.

I then turned on the water. pump to bring the water system up to pressure. The solar panels jumped from supplying 0.4 amps to supplying 1.2 amps. It supplied 1.2 amps for less than a minute and returned to 0.4 amps, the load of the two LEDs.

Obviosly LEDs draw little and though the water pump draws a lot, generally it doesn't run very long.

The pump probably ran for 10 seconds and the panels provided 1.2 amps for 45 seconds.

With a generally partly cloudy day our two solar panels, two forty watters seem to be peaking at 36 watts.

I determined this by turning on the fridge to 12 volts dc. Ivcan see the fridge on 12 volts pulls more power than the panels can supply, gradually draining the battery. With the fridge running solar panel output has been between 2 and 3 amps, 24 to 36 watts.

Of course we never run our fridge on 12 volts but it's good exercise for the panels.
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Old 07-11-2013, 11:36 AM   #16
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Name: Ryan
Trailer: 1979 Scamp 16- side bath
Virginia
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Norm--Thank you so much for your testing!


I was tempted to get some flexible panels$$$$ for the roof, but opted for a cheap hard 75watt panel from solarblvd.com , and Morning star PWM 6amp controller.
I'll just be using a voltage meter to monitor battery capacity as opposed to a fancier amp meter.

I received my panel yesterday and have quickly wired it up last night and today, as I'm leaving for a music festival in a few hours, Red Wing Roots festival in Mount Solon Va.

I have not had time to test the amp output of the panel in the shade, only the voltage. Under the current rainy overcast conditions the panel has a voltage of about 20volts. Under the heavy shade of trees the panel has a voltage of 17.75-18volts. I'm not sure if the voltage provides much info as compared to a real amp output measurement, but its all I had time for.

Anyways, I got a 14 gauge 50' extension cord, clipped off the ends and soldered on some high quality hobby grade connectors. I used the same connectors on the panel lead, as well as the solar controller lead.
For now I can place it in the sun as needed with the 50' cord while we are parked in the shade. If I find that it will in fact provide adequate charge power in the shade, then I may install on the roof in the future.
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Old 07-11-2013, 11:52 AM   #17
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Ryan,
It surprise me on how little electric power it takes to power the trailer when it's not winter camping and one has all LED lighting.

Enjoy the music festival. We love live music.
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Old 07-11-2013, 11:59 AM   #18
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Watching my meter last weekend I can attest that panel voltage is very deceiving. I've seen my panel sit at 42 volts and have very different amp readings based on shade, sun exposure/angle, and temperature. I've also seen the panel in hard shade drop it's voltage by half but still push more amps than poor sun exposure at higher voltages.

The best way to know how well your panel functions is by watching the amps it's producing or pushing into your batteries. Battery voltage will also be a good indication if your panel is doing anything. If my batteries aren't hitting the required charging or float voltages I know the panel isn't performing well at the location I'm parked, either that or it's a rain storm like most of my camping trips!
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Old 07-11-2013, 12:30 PM   #19
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Trailer: 2008 13' Scamp
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Originally Posted by Ryan P R View Post
Norm--Thank you so much for your testing!


I'll just be using a voltage meter to monitor battery capacity as opposed to a fancier amp meter.

.
I didn't see any need for a fancy battery monitor either but I did blow a whole $2.97, delivered to my door, for a voltmeter that I've permanently installed.

I can tell at a glance how the solar cells doing as well as always knowing what charge level the battery's at. After awhile you can tell at a glance if the solar cell output is dropping off because of shade etc.

I put a switch on the meter so I could turn it off overnight but one little bonus is that it gives a soft blue glow that acts as perfect night light.
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Old 07-11-2013, 01:13 PM   #20
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Name: Norm and Ginny
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If your solar panels are producing a really high voltage it would seem to me that your battery is basically fully charged and the solar controller is off, not supplying current to the battery because the battery doesn't need it.

A reasonable method of checking solar current is to load the system. When I did the little test for Ryan, there was virtually no current flow from the solar panel to the battery until I turned on lights in the trailer. As it was current flow from the solar panel pretty much matched the current draw of the items I turned on.

A reasonable test is to take the battery out of the equation and simply run the solar output thru an amp meter, measuring the short circuit current.
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Old 07-11-2013, 01:15 PM   #21
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Trailer: 2012 Escape 19' /2010 Honda Pilot 4WD TV
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I've got 2 panels mounted on my Escape 19 and almost always camp in the sun if we are boon-docking. The trailer is pretty well insulated and I roll the awning out if I want shade. Since most other campers want shade I can almost always get a sunny spot to camp. Even a little shade takes away a lot of solar charging power. For example, about 2" x 12" of shade on the edge of one of my panels from the Maxi-Fan will cut the panel output by 75%. I've since taken care of that by raising my panels. My 95 watt panels put out around 6 amps each in full sun and an overcast day I will sometimes see 1.5 amps or less. If you have solar you want sun. If you have portable panels you can park your trailer in the shade and move your panels into full sunlight...the best option for some. Most solar chargers have a display panel showing charging amps and battery voltage so you don't need any of those aftermarket meters. I bought one and never use it.
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Old 07-11-2013, 01:44 PM   #22
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Here's one guy's experiment with repect to how long you have to "rest" a battery before you get an accurate idea of the battery's state of charge. Note also Trojan's opinion of open circuit voltage measuring.

Reader's Digest version: after a little over two minutes on the charger, the battery voltage still wasn't correct after more than 11 hours of battery rest.

Just my (well his) 2 cents worth...

Measuring A Lead Acid Battery State of Charge Photo Gallery by Compass Marine at pbase.com
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Old 07-11-2013, 02:50 PM   #23
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Trailer: 2008 13' Scamp
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I've always been aware of the surface charge after charging and I've always used a load like turning on a light etc. to remove it before judgeing the battery state.

Maybe removing the surface charge in an inexact way isn't lab level accurate but at the end of the day my brain converts the battery condition level into a basic poor, fair, good or excellent
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