Solar Power and shade

[J Mac]

theres been a few posts on the thread, Trailer Cover, on the effect of shade on solar panels. Some say a completely covered panel can and does produce a charge. Others say a fully shaded panel can produce a charge, and some have said that they received a charge on their panel even tho it was covered with a CalMark trailer cover. Although these findings go against my experience and the many articles I've read it is very good news indeed.
Here are two such articles that confuse me:
Shading | PVEducation

Power Characteristics of a Solar Panel

so my question is...what the what

[Vermilye]

I'm one of the posters that has had a solar panel produce under a trailer cover. The specifics - the cover was Escape's brand, the panel their GoPower 95 watt. With winter sun, and no clouds, I got between .1 & .5 amps charging current. It was enough to keep the batteries full over the winter.

That said, even a small amount of shade drastically cuts down the output of a panel. I can watch even thin clouds cut the output of my panel by half. I currently have two panels, the original GoPower & a 100 Watt Polycrystalline Photovoltaic Solar Panel from Windy Nation. I chose the panel as the closest match voltage wise to the already installed 95 watt panel. They are wired in parallel, and even if one is in the shade, the other still produces its normal output.

[alanmalk]

I am also one of the posters...

Yesterday, I did a before and after test, by measuring the output of my 150 watt portable panel with and without a cover (flannel sheet in this case). Without the cover it produced 70 watts, with the cover - 2 watts. This is in line with my expectations for Colorado in the winter (4 weeks from winter solstice), and keeping the panel horizontal.

2 watts might - and let me repeat - might - be enough to keep your batteries stable over the winter - if fully charged to begin with, and carefully disconnected from even the smallest load. A check with a volt meter once per month can give you the information you need to confirm this is working.

But if you want to "set and forget" for the entire winter, then others have suggested a 10 watt panel outside the cover, and aimed at the noon sun for your location. In northern latitudes I have seen solar panels mounted vertically on walls. I presume because this is the best compromise...

--
Alan

[padlin]

For Arvada,

Optimum Tilt of Solar Panels by Month
Figures shown in degrees from vertical

Jan Feb Mar Apr May Jun
34° 42° 50° 58° 66° 74°

Jul Aug Sep Oct Nov Dec
66° 58° 50° 42° 34° 26°

[alanmalk]

Originally Posted by padlin

For Arvada,
...

Not having a cover, and with the battery switch in the "off" position, I'm blessed with a surplus of wattage in the winter from the Escape solar panel.

And I NEVER want to be camping in Arvada!

--
Alan

[soultrek]

Some non-scientific observations: My controller charge light has come on during dawn and dusk, and with cloud cover; it takes considerably longer for my battery to reach full charge in the Fall versus late Spring and Summer; the charge light comes on when the 60W light bulb above the solar panel is turned on during winter garage storage. FWIW…Glenn.

[santacruzer]

I checked my solar charge Saturday BEFORE removing my CalMark cover for the upcoming Thanksgiving trip. At high noon here in coastal California, cloudless day, Latitude:N 36° 58' 26.8216" I was pulling .2 amps through the cover. Not much, but something. It's the 160 watt panel.

[J Mac]

Originally Posted by santacruzer

I checked my solar charge Saturday BEFORE removing my CalMark cover for the upcoming Thanksgiving trip. At high noon here in coastal California, cloudless day, Latitude:N 36° 58' 26.8216" I was pulling .2 amps through the cover. Not much, but something. It's the 160 watt panel.

Out of curiosity, how much power is .2 amps. I tried Google for an answer and ended up with more questions than I started with. Will .2 amps light an LED bulb or be enough to trickle charge a 12 Volt or two 6 volt batteries over a 12 hour period?

[padlin]

I put a piece of cardboard on the corner of my panel, 0A output. So you can too much shade for any output.

[santacruzer]

Originally Posted by J Mac

Out of curiosity, how much power is .2 amps. I tried Google for an answer and ended up with more questions than I started with. Will .2 amps light an LED bulb or be enough to trickle charge a 12 Volt or two 6 volt batteries over a 12 hour period?

I imagine it's enough for an LED light bulb or two, but I don't know about battery charge. And I don't know about your 12 hour period...full sun wouldn't be on the panel except for a few hours each day in the winter, and even then the panel is flat and not tilted properly.

[J Mac]

Originally Posted by padlin

I put a piece of cardboard on the corner of my panel, 0A output. So you can too much shade for any output.

This is the very experience I have encountered.

[J Mac]

Originally Posted by santacruzer

I checked my solar charge Saturday BEFORE removing my CalMark cover for the upcoming Thanksgiving trip. At high noon here in coastal California, cloudless day, Latitude:N 36° 58' 26.8216" I was pulling .2 amps through the cover. Not much, but something. It's the 160 watt panel.

As a test, it'd be interested to know how many amps, if any, there might be if your solar panel was completely covered with an opaque cover at high noon. I know your off on a Thanksgiving trip (lucky you) and the CalMark cover is off.

[tractors1]

12V x 0.2 amps = 2.4 watts

[J Mac]

Originally Posted by tractors1

12V x 0.2 amps = 2.4 watts

Thanks tractors! Is that about the wattage needed for a solar calculator or doesn't electricity work that way?

[tractors1]

Originally Posted by J Mac

Thanks tractors! Is that about the wattage needed for a solar calculator or doesn't electricity work that way?

Probably less for the calculator. I once did a business deal using a cigarette lighter to power a solar calculator in a dimly lit drinking establishment.

[santacruzer]

Originally Posted by J Mac

As a test, it'd be interested to know how many amps, if any, there might be if your solar panel was completely covered with an opaque cover at high noon. I know your off on a Thanksgiving trip (lucky you) and the CalMark cover is off.

It was completely covered with an opaque cover at high noon when I made the observation you're quoting.

[Vermilye]

With an opaque cover over the entire panel, I wouldn't expect to get anything. As to .2 amps being enough to maintain your batteries, it is a bit on the low side, however the best way to check is to look at the battery voltage after dark (when the solar panel is inactive). If the battery voltage is in the neighborhood of 12.6 volts, you are OK. If you get down to around 12.06V (50%) you need to throw on a charger or remove the cover & let the panel do its thing.

Another consideration - according to Trojan, a fully charged battery won't freeze until the temperature reaches -90°F, but at 40% charged, the freezing temperature of your battery is 16°F, a temperature some us (the unlucky ones) may reach over the winter...

[J Mac]

Originally Posted by santacruzer

It was completely covered with an opaque cover at high noon when I made the observation you're quoting.

Opaque | Define Opaque at Dictionary.com

Wow, It seems your solar panel doesn't need any sun light to create a charge. Somehow this just doesn't seem right.

[cpaharley2008]

You say tomato, I say tomato...take it for what it's worth.

[santacruzer]

Originally Posted by J Mac

Opaque | Define Opaque at Dictionary.com

Wow, It seems your solar panel doesn't need any sun light to create a charge. Somehow this just doesn't seem right.

Through a glass darkly...maybe opaque isn't the correct adjective. What say we bury this dead horse??