Solar Panel output in the shade? - Fiberglass RV
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Old 07-01-2013, 07:00 PM   #1
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Name: Ryan
Trailer: 1979 Scamp 16- side bath
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Solar Panel output in the shade?

I'd really like to mount solar panels on my roof so I don't have to mess with setting them up or storing them inside of the trailer.

On the other hand we always camp in the shade! I realize that shade from trees will dramatically reduces the performance of solar panels, but they've still got to provide some charging power right? How much?

My quick math tells me that 15-20 amps of charging per day should more than cover my needs in nearly every situation. So I was thinking if I put 100watt solar panel on my roof (max output of 5.8amps) and I only average 1.5 amps or so per hour on average-while parked under the shade of trees- that should do the trick.
The problem is I don't know how much output these panels will produce in the shade, or if any useable amount at all. To be clear, I'm not talking about a partially shaded panel, I'm referring to a panel completely shaded from DIRECT sunlight by the tree canopy. Surely the indirect sunlight has to provide enough light for the panel to have "some" output... Or so I hope.

I already have all LED lights, a low amp draw water pump, low draw furnace 1.8amps, and low draw fans....
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Old 07-01-2013, 09:08 PM   #2
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That is a good question and one which one of our solar powered members should be able to address. My gut feeling is that "deep shade", i.e buried in a forest, you will not get much. They do put out a fair amount on cloudy days but that is not the same as heavy forest canopy.

I intend to put a big panel or even two on my roof. Perhaps two 100-140 watters if I can fit them up there. Then I will have one more that is mobile for the "just in case".
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Old 07-01-2013, 09:32 PM   #3
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Several years ago I stayed in Yellowstone for a week.
The Campground was among 60 to 80 feet tall pines, so no direct sun.
My flat roof mounted 50W panel never let me down.
In September the nights get pretty cold so the furnace was on every night.
All of my lighting was LED so that may have helped.
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Old 07-01-2013, 10:55 PM   #4
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In bright sun my solar panel puts out over 19 Volts but it comes the wire to the inverter panel it reads 12Volts. In the shade and overcast the panel will charge some.
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Old 07-02-2013, 06:11 AM   #5
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I don't have a problem keeping up with normal usage in light shade using a 95 watt panel, however heavy shade for a couple of days will start to drop the batteries. I have a pair of 6v batteries, LED lighting, etc. I do use a 1000 watt inverter to make a pot of coffee each morning that draws around 10 amp/hrs.

With careful use I've been able to camp without a generator for up to two weeks in partial shade.
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Old 07-02-2013, 06:37 AM   #6
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It all comes down to math and a volt meter. You won't know if it'll work until you try it. Maybe you could borrow one from someone and just put it up on the roof when you camp the next time to see if it will work for you.
Some panels work better in the shade than others. Do some homework on that front.
My 64 watt panel puts out more energy than my 125 watt panel in the the shade.
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Old 07-02-2013, 10:16 AM   #7
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The best thing I bought to monitor shading issues was a proper meter. I use a Tri-Metric. My older 75w panel worked fine in good sun but once it had even slight shading it's voltage dropped and amps dropped even more. I changed panels this year because of it. I'd recommend a good meter even if you don't have a solar panel.
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Old 07-02-2013, 10:18 AM   #8
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It all comes down to math and a volt meter. You won't know if it'll work until you try it. Maybe you could borrow one from someone and just put it up on the roof when you camp the next time to see if it will work for you.
Some panels work better in the shade than others. Do some homework on that front.
My 64 watt panel puts out more energy than my 125 watt panel in the the shade.
What type/brand of panel is your 64 vs your 125 watt panel?

Unfortunately I don't know ANY other RVers, and definitely no one that has a panel for me to borrow for experiments. My friends either don't camp- or backpack/carcamp.
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Old 07-02-2013, 10:28 AM   #9
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And is there a way to select a solar panel that does "work in shade". I have done a lot of reading on solar and what I seemed to be reading is that shade in any given cell causes a high resistance in that cell which affects every other cell in series with that cell. In some cases it seemed to entirely shut off the cell that was shaded, or so it appeared.
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Old 07-02-2013, 10:46 AM   #10
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Decent panels will have bypass diodes built in to assist with shading problems, however I wouldn't expect to park under a tree and get much out of a panel. More efficient panels are also much more expensive. I'm currently experimenting with a higher voltage panel to see if it helps in shaded areas, it's roof mounted and runs around 42v. My first trip this year was in a 3 day rain storm and it still managed to put out up to 8amps depending on how heavy the cloud was. I wasn't facing south so I was happy with the performance. However running a higher voltage panel will require a different controller so that might not be the solution for everyone.
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Old 07-02-2013, 11:45 AM   #11
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I am starting from scratch and have been looking at starting with the higher voltage panels. They are less common = more expensive though.
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Old 07-02-2013, 12:50 PM   #12
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My 64 watt is Unisolar
My 125 watt is US Solar
Unisolar does not make the 64 in a panel anymore. Sometimes you can find one on Ebay. They areflexible in an aluminum frame. I had a tree branch fall on it and bend the frame with no effect (I bent it back). Most panels come in glass -as did my 125. Unisolar does make the 64 w in a roll out panel but it's pretty long.
US Solar is still in business and I paid $2 a watt delivered. That's watt (LOL) you want to look for the - $ per watt.
As always, do your research.
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Old 07-02-2013, 01:07 PM   #13
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Ryan, I think fully charging your battery and doing some front yard pretending is the way to work it out. This will give you a good image of what you use for power.

We have a 10 amp dc voltmeter that we use to measure the solar panel's current output. It could also be used to measure current draw from the battery by inserting it in the lead from the battery to the trailer.
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Old 07-02-2013, 03:39 PM   #14
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Although it takes a little extra set up time, it sounds like the portable panels would work best for your needs. The people here on the forum really like the flexibility it offer them.
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Old 07-04-2013, 10:36 AM   #15
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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, 10:36 AM   #16
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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, 10:52 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, 10:59 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, 11:30 AM   #19
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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, 12:13 PM   #20
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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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