Effect of Partial Shade on Solar Panel Output?

[Sunny1]

I'm camping in an area that has partial shade.  My Renogy 200 watt starter kit with MPPT controller is producing adequate power for LEDs, propane refrigerator control panel @ 14 amps/day, and for charging 2 tablets, 2 cell phones, and a Verizon Jetpack hotspot.

I am curious to know how much partial shade affects my solar panels and can't find any numbers.  I am severely math challenged, so would appreciate very simple instructions on figuring how many amps per day I am actually producing and using. 

On a good day, my battery bank ends up charged at 13.11 (2 100 watt AGM's).  By morning, it is around 12.75.

As I understand it, AGM batteries are fully charged at 13, instead of 12.7 for flooded batteries.

The only solar usage chart I have ever understood is Bob's solar panel capability chart for dummies that shows exactly which devices you can use with various size solar arrays.

Would appreciate any explanations that I can understand.  

 

[Spaceman Spiff]

https://handybobsolar.wordpress.com/the-rv-battery-charging-puzzle-2/

About 3/4 of the way down the article, under 'NEW INFO & PHOTOS ADDED JULY 26, 2009:' he talks about shading and shows pictures.  Read the whole thing, you'll learn something (I had to read it three or four times before I understood).

 -- Spiff

 

[John61CT]

The more small PV units between smart diodes & controllers the better, rather than big dumb slabs.

Am I right?

Bob is fantastic, just be aware his ** very strong ** opinions might just color where he stands on PWM vs MPPT.

I haven't dove (diven?) down the rabbit hole just yet, but this very issue seems to be a big factor in the choice.

Victron's flexible line of BlueSolar MPPT manuals have additional info, but as Bob says, everyone's trying to separate you from hard-earned money.

 

[Sunny1]

Spiff, that section at the bottom was very helpful. Shadows ARE a big deal. I suppose the reason I am managing my small electrical needs is due to the patches of full sun I get throughout the day.

Thanks for that link!

John, I had tried to understand some of Handy Bob's articles before, butcouldn't grasp them too well. And I'm aware of his very strong opinions! ;D

I know that my Renogy panels have lots of cells and are supposed to compensate for some shading. But probably not as much as I hoped. On rainy days we miht have to go for long drives with my cigarette lighter plug with 4 USB cables plugged into our devices to get them charged.

I do appreciate answers to my very ignorant questions!

 

[GotSmart]

I have a similar set up, but with 4 6v batteries (448 AH, series paralell)  today under extreme heavy clouds my batteries are resting at 14.3 volts. This with a PWM controller, and monochrystaline panels.  IMHO, those make a huge difference in low light charging over polychrystaline.  There are improvements happening all the time. The latest from Renogy is called the Eclipse.  

• Monocrystalline panels come with high-efficiency cells that help increase module efficiency. Module efficiency: Eclipse 100W Monocrystalline: 18.35%, regular 100W Monocrystalline: 15.47%, 100W Polycrystalline: 14.56%.
• Bypass diodes minimize power drop caused by shade and ensure excellent performance in low-light environments.

The reason that there are no answers to your question, is that it is impossible to quantify the photovolantic (PV) potential (amount of energy able to be captured) of every location along with every variation of atmospheric or shade situation not to mention type of panel..  

Location in the US makes a difference.  Quartzsite AZ has twice the potential as Seatle WA on a yearly average. cloud cover makes a difference.  Elevation makes a difference. The higher you are above sea level, the greater the PV potential.  In training I was warned about having to upgrade the controller capacity for systems used at higher elevations. Some controllers will burn out that would function perfectly at sea level.  Temperature is also a factor.

 

[John61CT]

Cloud cover filtering/scattering solar input is a completely different issue from actual shadows cast by solid objects, e.g. dappled

 

[GotSmart]

Unless you are parked in the direct shade of an old growth forest, the difference is small in all the variables.

 

[John61CT]

I'm considering actually going with lots of smaller completely separate panels, say 20 or 50W range.

With something like the Victron BlueSolar 100x line, maybe six in series before paralleling? Headroom on the amps size would let me experiment replacing with larger sizes later?

Fringe benefit is longer/thinner wires, park in the shade, slide the big panels out away from the van/controllers.

Just spitballin' please tell me why it's silly?

 

[GotSmart]

Things depend on how  the panels are constructed.  This might help.


http://www.solarchoice.net.au/blog/partial-shading-is-bad-for-solar-panels-power-systems/

[font=Verdana, sans-serif]You can think of a string of panels as something like a piece of pipe, and the solar power is like water flowing through that pipe. In conventional solar panel strings, shade is something that blocks that flow. If, for example, shade from a tree or a chimney is cast on even one of the panels in the string, the output of the entire string will be reduced to virtually zero for as long as the shadow sits there. If there is a separate, unshaded string, however, this string will continue to produce power as per usual.[/font]

[font=Verdana, sans-serif]In extreme cases, a shadow does not necessarily need to fall on an entire panel – depending on the technology used in the solar panel in question, shading of even just one cell could flatten the output of the panel and in turn the entire string. Many modern panels, however, come equipped with devices called bypass diodes which minimise the effects of partial shading by essentially enabling electricity to ‘flow around’ the shaded cell or cells.[/font]

If you have a main line, with each panel feeding it individually, this will also help virtually eliminate any effect of shading in old style panels. 

Series is not your friend.  Smaller is more expensive per watt

https://www.amazon.com/Solar-Panel-...68214&sr=8-12&keywords=solar+connection+wires

 

[Sunny1]

Duplicate

 

[Sunny1]

John and GotSmart, your input helps a LOT!

I have the Renogy 100 watt monocrystaline panels with 18.4% efficienciency.  I read that for this time of year in Florida (sea level) they should be tilted 45 degrees.  I make sure to move them 3 or 4 times a day to keep their shadow directly behind them.

Here are two photos of our site. The light was low, so shadows were long.  Some of the time the sun hitting the panels is bright and high, but mostly not.  I am truly amazed that they are producing enough power for our very modest needs under these conditions.

We move the 12th to another campground and our site there will be full sun.

I'm sure I'll feel delirious with power then!

 

[Spaceman Spiff]

I'm considering actually going with lots of smaller completely separate panels, say 20 or 50W range.

I agree with GotSmart:  Unless you get a real good deal on small panels they are more expensive per watt than larger panels; and they are heavier per watt.

With something like the Victron BlueSolar 100x line, maybe six in series before paralleling? Headroom on the amps size would let me experiment replacing with larger sizes later?

The output of all cells/panels in series will be reduced to the output of the lowest cell/panel.  One big reason for paralleling multiple panels in mobile applications is that if one panel is partially shaded the other(s) will still deliver full power (can't do much about the internal construction of the panel itself).

Fringe benefit is longer/thinner wires, park in the shade, slide the big panels out away from the van/controllers.

This is a good strategy for portable panels.  The downsides are:

• you get no solar benefit while traveling,
• the panels are more easily stolen,
• you must have a place to store them and their extension cords when not in use,
• if tilted, the tilting mechanism adds weight and bulk,
• you may have to  periodically move them to keep them in the sun/track the sun.

Just spitballin' please tell me why it's silly?

Not silly, it just depends on your situation and camping style.

  -- Spiff

 

[Sunny1]

Update on the partial shade solar performance.  We also have had fog and heavy smoke from a prescribed burn that no one warned us about!

In spite of all that, the lowest battery reading I have seen is 12.41.

We are finally moving to a campground where we will get full sun today.

Yay! ?