Solar Panels and Shadows...

[Diesel Duck]

While surfing the internet I came across this Vlog featuring a couple equipping their new catamaran with solar panels and thought some of you might be interested in seeing their test results:

 

[JDCAVE]

Thanks for that post DD. I'm hooked up in parallel. I get the most consistent performance under "cloudy-bright" skies.

Jim
Sent from my iPad using Trawler Forum

 

[READY2GO]

Very interesting results with the shading tests. It seems blocking part of one or more cells cuts output by 40% to 50% but blocking even one whole cell cuts the output by as much as 90%. Good info to have.

 

[foggysail]

Until this season, My 4 150 watt panels delivered just shy of 25 amperes for most of the day. This year my max is around 20. Now of course I never washed the panels but that is high on my list to do soon.

Others may have this same dirty problem

 

[FlyWright]

That would be a good test....before and after the washdown. Don't forget the pictures for comparison. We like pictures.

 

[foggysail]

I'll take pictures but there is a but! I long ago gave up trying post pictures in forums. Now this forum may be different but other forums want pictures from web sites only. That would mean I have to download to some yet to be determined site before posting.


I will post the results but the best I can offer is to email the pictures to somebody and let them post them

Back to solar! I set up an automatic transfer switch ( a relay in layman terms) to switch to a 2KW true sine wave inverter in the absence of AC from either dock or my genny power. My battery bank consists of 4 East Penn golf carts to make up two 12v banks which I connect in parallel. This provides 440 AH of battery.

I have an 8 cubic foot fridge on the boat with self defrost. We have 2 32" tvs plus lighting. And yes I also have a Xantrex 50 amp charger which for the most part only charges the generator battery.

The panels! Those things replace all the consumed battery power every day we are out unless its raining. I highly recommend solar for boats. Homes are another matter requiring much discussion.

 

[Peter B]

I'll take pictures but there is a but! I long ago gave up trying post pictures in forums. Now this forum may be different but other forums want pictures from web sites only. That would mean I have to download to some yet to be determined site before posting.

You don't have to do that foggysail. Although you can do that, and some keen types do, using dropbox iCloud or similar, and just clicking on the "add an image icon at the top of the input window. But...this forum software is very user friendly, and you can post multiple pics as long as they are not too huge, right off the computer you're working on.

Just make sure you're in 'advanced post' mode, not 'quick reply', which is automatic if you click on the reply button rather than just posting in the quick reply window, but even if you were, there is a button below it labelled 'go advanced', so that will take you to the advanced post window.

You then click on manage attachments, then click on 'choose file', which takes you via browse, to your computer so you can browse to your photos, then just click on the photos you want just repeating eh selecting process, then when you have the pics chosen, you click on 'upload', and (most important) WAIT, for the upload to complete by watching the blue line across the top or whatever your computer does while it is uploading. Then scroll down to the bottom and click on 'close this window', then select submit post from the bottom of the window where you pic files are listed, and bob'syeruncle...pics posted - 'piece of cake.'

 

[Searios]

Parallel and Series connection

Excellent video, thanks...it got me thinking about my setup which is both in series and parallel...I am installing 4 x 230W, 41V semi flexible panels in a series/parallel configuration creating about 82V for the Mastervolt SCM60 MPPT-MB charger.

The 4 panels will be placed in a row (front to aft) along the top of the bimini, The mast is right behind the bimini so it creates some shading on the 2 panels closest to the mast...

There are several ways to connect these panels: number 1 + 4 in parallel and number 2+3 in parallel, then series connect them. Or parallel number 1+2 and 3+4, then series connect them...or parallel number 1+3 and 2+4....you get the picture...

I'm wondering what would be the best set-up for these 4 panels.

 

[Searios]

This is my Bimini...:

 

[foggysail]

I have both 12v and 24v systems on my boat, only the 12v is connected to the solar. But why are those of you who have higher voltage panels going with higher voltages? The only advantage I can see is being able to use smaller wire from the panels to your MPPT controller/regulator. Personally and I do mean for me, I don't want any subsystems that operate above 48v for safety reasons.

My panels operate in parallel mode with two each wired together using #10 wire. So I have a total of 4 wires from my panels to a solar regulator......have to look at to get the manufacturer's name but it is a quality regulator not a $10 Ebay special. By the way, those inexpensive things on Ebay do work although I doubt they provide battery equalization.

 

[Searios]

Its not for safety:https://www.physics.ohio-state.edu/~p616/safety/fatal_current.html

 

[healhustler]

Great info, DD. I've gone to quite a bit of trouble to clear my pilothouse roof and remove the likelihood of shading. Sounds like it may have been worth it.

 

[AusCan]

Good info.

I'm in the process of working out the best layout for panels. I was concerned about the shade from my vhf antenna, but it looks like a narrow shadow like that has only minor effect. Makes my roof layout plans a little simpler.

 

[BruceK]

Thanks DD. Very helpful.

 

[foggysail]

Its not for safety:https://www.physics.ohio-state.edu/~p616/safety/fatal_current.html

????

 

[Diesel Duck]

This is my Bimini...:

Do I see dedicated racks built within the Bimini structure to support 12 solar panels? If so, I like it!

 

[dhays]

I finally had a chance to view the vid. I am amazed at how devastating any shade is to the output. It means that in my case a pilothouse roof installation would very limited if the sun drops low enough for the arch to cast a shadow on the panels. It makes it appear that in my case I would either have to mount them at the arch level, or just not bother.

 

[Searios]

Do I see dedicated racks built within the Bimini structure to support 12 solar panels? If so, I like it!

Yes, the middle section frame holds 4 panels. I have also decided to install them in parallel only due to the video, so thanks for posting it..

 

[Cottontop]

I have read that when a solar panel is shaded, it will automatically reduce its output by 50% to "protect itself." I don't pretend to understand this, but it is consistent with the results in the video. The video also indicates that if more than one panel is shaded, output may be almost eliminated.

I have also read that "microinverters" (e.g., Enphase) can be installed on panels to solve this problem. I don't know anything about this, either, but maybe others do.

 

[psneeld]

I have read that when a solar panel is shaded, it will automatically reduce its output by 50% to "protect itself." I don't pretend to understand this, but it is consistent with the results in the video. The video also indicates that if more than one panel is shaded, output may be almost eliminated.

I have also read that "microinverters" (e.g., Enphase) can be installed on panels to solve this problem. I don't know anything about this, either, but maybe others do.

I would read up more on shading...I don't believe that power is reduced to protect themselves (solar panels) and there are variations in panels themselves aND how they are set up.

Here is a link I found helpful...along with many other generic internet articles...

mv.VikingStar: Solar Panels on the Boat - Modeling and Performance

 

[Cottontop]

I would read up more on shading...I don't believe that power is reduced to protect themselves (solar panels) and there are variations in panels themselves aND how they are set up.

Here is a link I found helpful...along with many other generic internet articles...

mv.VikingStar: Solar Panels on the Boat - Modeling and Performance

Here are three sites that discuss potential damage to solar panels from shading, and strategies to deal with shading. One strategy is to use "bypass diodes," which is what your link used. Apparently some panels have bypass diodes pre-installed, but output is still sharply reduced by shading.

How Does Shade Affect Solar Panels | The Eco Experts

The Effect of Shade on Solar Panels | Wholesale Solar Blog

Effects of Shading on Solar Panels - Solar

 

[dannc]

...
I have also read that "microinverters" (e.g., Enphase) can be installed on panels to solve this problem. I don't know anything about this, either, but maybe others do.

Panels produce DC power and most houses need AC power. At some point, the DC has to be converted to AC and for most house PV systems, this is done with a single large inverter. The PV panels are connected in a string and any panel that is shaded on that string impacts the power output of the whole string.

Enphase's microinverters are installed at each panel instead of having a single inverter. The inverter convert the panels DC to AC which is then wired into the house. One advantage of this approach is that shading of a single panel has no impact on the other panels in the system since each panel has it's own inverter.

Last time I looked at Enphase's product line, they were targeting grid tied solar installations and they were converting the DC at each panel to power the AC in the house. Not a bad approach to solve that specific problem in a grid tied house.

Later,
Dan

 

[MurrayM]

I'm thinking of putting two solar panels on the pilothouse roof. Instead of combining them (where if one is shaded the efficiency of both are reduced) wouldn't it make sense to wire them independently to the charge controller? Then, if one is shaded and the other isn't, at least one of them would be charging as it should?

 

[psneeld]

On many boats there are few spots that don't get partial shade part of the day.

I think many off grid panels now have diodes in them as all the ones I was considering had them.



I have 2 panels on hinges that fold up or down and the next two I will keep portable just for the shading issue. While I could see hard shading as described in one of the links causing hit spots, I don't see the partial shading that a boats superstructure or rigging causing damage. The solar threads I have followed never seem to discuss that as an issue, just reduced output.

 

[Cottontop]

On many boats there are few spots that don't get partial shade part of the day.

I think many off grid panels now have diodes in them as all the ones I was considering had them.



I have 2 panels on hinges that fold up or down and the next two I will keep portable just for the shading issue. While I could see hard shading as described in one of the links causing hit spots, I don't see the partial shading that a boats superstructure or rigging causing damage. The solar threads I have followed never seem to discuss that as an issue, just reduced output.

Right now my design has an arch over the top of the solar farm, so some panels will always be shaded. Relocating the arch may be impractical, so I'm trying to learn about these micro-inverter systems that may solve the problem.

 

[psneeld]

I think installing panels that will always have partial shading is a problem. Not from a damage point but from a performance standpoint.

Not sure that micro -inverters are what you are looking for in off grid applications like a boat. I thought they are for on grid setups. I understand your concern for shading, but most boat applications only use solar to charge battery bsnks, not go straight to AC.

https://www.sullivansolarpower.com/about/solar-power-blog/daniel-sullivan/dangers-of-micro-inverters

 

[Cottontop]

I think installing panels that will always have partial shading is a problem. Not from a damage point but from a performance standpoint.

Not sure that micro -inverters are what you are looking for in off grid applications like a boat. I thought they are for on grid setups. I understand your concern for shading, but most boat applications only use solar to charge battery bsnks, not go straight to AC.

https://www.sullivansolarpower.com/about/solar-power-blog/daniel-sullivan/dangers-of-micro-inverters

I think the micro-inverter systems are typically for grid-tied houses, but Enphase has a complete system with micro-inverters on the panels (if 10% of the array is shaded, you get 90% output), and LiFePO4 batteries with micro-inverters on them, as well. I'm trying to learn whether it will work on a boat. I can live with 90% output, but not 50%, or 10%. They have started selling their batteries at about $800/kwh. The batteries are a little heavier than other LiFePO4; I suppose that's the micro-inverters.

 

[twistedtree]

I'm finally back in the land of internet-o-plenty and watched this video. Oh my, what a huge disservice it is. Well intentioned of course, but so wrong in so many ways. The biggest problem is that they don't understand how the outback charger works, and aren't letting it adapt to the shaded panel configuration.

The parallel results are just about right. Those "squares" on the panels are typically wired in series to create whatever is the nominal panel voltage. For arguments sake, let's say each panel is 2V and the panel total is 20V. Then you put two panels in parallel like in their experiment. Turn on the charge controller and let it settle in and it will be converting the 20V panel voltage to the 12V charge voltage. All is good. Now shade one square and that panel's voltage drops to 18V while the other remains at 20V. The parallel panel is now contributing zero, zilch, nada, nothing. This is the basis for people saying that slight shading of a panel will pretty much kill all power.

BUT.... if you left the setup like that for a while, the outback charger would rescan and likely start operating at something closer to 18V converted to 13V, and you would likely pick up a bunch more power because the shaded panel can now contribute some current. You end up with both panels running at 18V, not just one, so it's effectively like shading a square on all parallel panels.

Now, do the same thing in the series configuration. In series the panels are 40V and the outback converts to 13V charging voltage. Shade one square and the voltage drops to 38V. I'd stake $$ that the reason the output plummets is because the outback needs to rescan and readjust, and they aren't waiting long enough for that to happen. If they let it readjust, the panels would operate at 38V converting to 13V charge, and the loss is one square's worth of power, not two as in the parallel case.

Arguable the erroneous results are because the outback is slow to re-calibrate to the new output voltage. People have complained about this behavior in off-grid applications. But the result in the video experiment is another variable (the outback controller) that they are unaware of and have no control over, yet it directly impacts the results.

And if that's not enough, the blocking diode arrangement inside each panel can have a huge impact on shading results. I have no idea how their test panels are wired, but inadequate blocking diodes can cause much greater power drop from shading that with proper blocking diodes. With the diodes, the shaded panel not only doesn't contribute any power, but it actually becomes an additional load on the remaining panels. So your results with your panels may be different from your buddy's with some other panels.

And if that's not enough, the use of an MPPT controller vs not, and the voltage of the panels vs battery voltage will also play a role in shading losses.

That video would be an amusing elementary school show and tell project, and poor high-school science project, and cause for selecting a new major in college.

 

[dhays]

Good info Twisted, thanks. I would love having some solar on this trip. It would help get those batteries topped off.

 

[BruceK]

Good info Twisted, thanks. I would love having some solar on this trip. It would help get those batteries topped off.

That`s the joy of panels, they just nag away the batts until they are full.
But, TT`s post casts a new shadow over panels. Do all regulators, or maybe all MPPTs have the capacity, like Outback, to regroup and get the best out of part shaded panels? How to tell which do and don`t, is it in the specs? I`m not expecting Brand X to confess: "this model has zero capacity to recalibrate to get optimum output from a part shaded panel".