Reply
 
Thread Tools Display Modes
 
Old 07-26-2016, 01:34 PM   #21
Senior Member
 
City: Houston
Country: USA
Join Date: Jun 2015
Posts: 155
Quote:
Originally Posted by psneeld View Post
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
__________________
Advertisement

Cottontop is offline   Reply With Quote
Old 07-26-2016, 01:44 PM   #22
Guru
 
City: NC
Country: US
Join Date: Jan 2014
Posts: 586
Quote:
Originally Posted by Cottontop View Post
...
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
__________________

dannc is offline   Reply With Quote
Old 07-26-2016, 02:42 PM   #23
Guru
 
MurrayM's Avatar
 
City: Kitimat, North Coast BC
Country: Canada
Vessel Name: Badger
Vessel Model: 30' Sundowner Tug
Join Date: Jul 2012
Posts: 2,578
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?
__________________
"The most interesting path between two points is not a straight line" Murray Minchin
MurrayM is offline   Reply With Quote
Old 07-26-2016, 04:05 PM   #24
Guru
 
psneeld's Avatar
 
City: Avalon, NJ
Country: USA
Vessel Name: Freedom
Vessel Model: Albin 40
Join Date: Oct 2011
Posts: 13,277
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.
psneeld is online now   Reply With Quote
Old 07-26-2016, 09:17 PM   #25
Senior Member
 
City: Houston
Country: USA
Join Date: Jun 2015
Posts: 155
Quote:
Originally Posted by psneeld View Post
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.
Cottontop is offline   Reply With Quote
Old 07-26-2016, 09:31 PM   #26
Guru
 
psneeld's Avatar
 
City: Avalon, NJ
Country: USA
Vessel Name: Freedom
Vessel Model: Albin 40
Join Date: Oct 2011
Posts: 13,277
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/a...icro-inverters
psneeld is online now   Reply With Quote
Old 07-26-2016, 09:57 PM   #27
Senior Member
 
City: Houston
Country: USA
Join Date: Jun 2015
Posts: 155
Quote:
Originally Posted by psneeld View Post
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/a...icro-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.
Cottontop is offline   Reply With Quote
Old 07-28-2016, 01:38 AM   #28
Guru
 
twistedtree's Avatar
 
City: Gloucester, MA
Country: USA
Join Date: Jan 2013
Posts: 2,304
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.
__________________
www.MVTanglewood.com
twistedtree is offline   Reply With Quote
Old 07-28-2016, 02:47 AM   #29
Guru
 
dhays's Avatar
 
City: Gig Harbor
Country: United States
Vessel Name: Kinship
Vessel Model: North Pacific 43
Join Date: May 2015
Posts: 2,786
Good info Twisted, thanks. I would love having some solar on this trip. It would help get those batteries topped off.
__________________
Regards,

Dave
SPOT page
dhays is offline   Reply With Quote
Old 07-28-2016, 03:12 AM   #30
Moderator Emeritus
 
BruceK's Avatar
 
Join Date: Oct 2011
Posts: 6,225
Quote:
Originally Posted by dhays View Post
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".
__________________
BruceK
Island Gypsy 36 Europa "Doriana"
Sydney Australia
BruceK is offline   Reply With Quote
Old 07-28-2016, 03:54 AM   #31
Guru
 
Insequent's Avatar
 
City: Brisbane River
Country: Australia
Vessel Name: Insequent
Vessel Model: Ocean Alexander 50 Mk I
Join Date: Mar 2012
Posts: 1,027
I have finally got my new panels setup. Previously I had 7 x 260W Suniva 30V panels. Now I have 6 x 345W Sunpower 60V panels. As I have a 12 V system I have 2 x Outback FlexMax 80's. I really wish I had gone to a 24V house bank as I would only have needed 1 FlexMax. So 3 of the new panels feed each charge controller. In order to have both charge controllers synchronise (in terms of float charging etc) they are linked to a Mate 3 unit.

So far I have not been at anchor or off shore power long enough to get a daily Ah replenishment figure. But a few days ago just before midday I had peak readings of 124.8 A and 1740W. Not too bad for the low angle winter sun! So I think I should get a very healthy amount of Ah during the day. Over the next few weeks I hope to get some data on this.

My new configuration is in part to minimise shading. The 2 panels on the pilothouse roof are 2' further forward to much reduce the effect of shading from the flybridge hardtop. Part of that project necessitated re-positioning the Sat dome. On the hardtop I have just 4 panels located forward. The new mast config involved modifying the deck mounted mast. The lower 5' was discarded and the top half, well top two thirds, mounted on the hardtop. The mast now has the sat dome on the old radar platform with a new radar platform below it. I did not install panels at the aft end of the hardtop near the mast. There would have been shading of them for a lot of the time. As it is the mast only causes some shading when I'm south-facing, but in summer that will be less of an issue as well.

I can lower my VHP antennas to reduce panel shading at anchor. They hinge at the bottom, so its just a 5 second task to raise or lower each antenna. If I get motivated one day at anchor I will try and quantify the shading effect from the antenna, bearing in mind Twisted's warning to allow time for the charge controller to re-scan. Does anyone know how long I would need to wait?

Pic from dingy shows mast, but panels are hard to see as there is only a small airgap between them and the underlying structure. The antennas are lowered. I'll try and remember to take a pic from shore in the morning to actually show the panels themselves before departing on my cruise to points north.
Attached Thumbnails
Click image for larger version

Name:	Mast panels Jul16.jpg
Views:	28
Size:	75.1 KB
ID:	54626  
__________________
Brian
Insequent is offline   Reply With Quote
Old 07-28-2016, 10:35 AM   #32
Guru
 
twistedtree's Avatar
 
City: Gloucester, MA
Country: USA
Join Date: Jan 2013
Posts: 2,304
The way an MPPT controller works is periodically it "scans" to find the maximum power point of the attached panels. The maximum power point is the voltage and current operating point for the panels that yields the maximum wattage. i.e. voltage multiplied by current.

Panels are a bit of an odd duck because they are what's known as a constant current source. As you vary the load on the panel, the current will remain nearly constant, and only the voltage will vary. So they will produce the same amount of current at any voltage, but only up to a point. Once the voltage gets too high, the current drops off, and it does so very fast - like a cliff. The result is that a panel's wattage output varies directly with the actual operating voltage. A panel's rated wattage is based on the highest voltage you can reach, just before the current plummets.

Now, go back to and MPPT controller. When it "scans" is varies the load on the panels while monitoring the voltage and current, and figures out where the optimal operating point is where it can extract the most watts (power). Then it settles in and starts running. An MPPT controller can do this because it is essentially a variable DC to DC converter. It takes whatever the best input voltage is, and converts it to the desired charger voltage. The only loss is in the DC to DC conversion and that's around 10%.

So what the video is really showing is the Outback's instantaneous response to shading, which is nearly meaningless. I haven't studied exactly how the outback or any other controller behaves and recovers in such a situation, but know that some experienced people wish the outback scanned more often. I suppose what you want in a controller really depends on the weather or other application factors. If you have stable weather without a lot of clouds, then less scanning and more producing is better. The outback leans this way. And if you have a lot of varying cloud cover or other variable shading, then you would prefer more scanning. But all MPPT controllers scan and adapt - it's the nature of the beast.
__________________
www.MVTanglewood.com
twistedtree is offline   Reply With Quote
Old 07-28-2016, 11:07 AM   #33
Guru
 
twistedtree's Avatar
 
City: Gloucester, MA
Country: USA
Join Date: Jan 2013
Posts: 2,304
Insequent - I'm envious of your solar setup. I sure wish I could get that many panels on my boat.

You may have already done this, but you might be able to take advantage of having two charge controllers. If you have some panels that are more subject to shading than others, try grouping the panels subject to shading on one controller, and the panels not subject to shading on the other controller. Then shading will only confuse one controller while the other can keep cranking away with stable sunlight.
__________________
www.MVTanglewood.com
twistedtree is offline   Reply With Quote
Old 07-28-2016, 11:23 AM   #34
Guru
 
dhays's Avatar
 
City: Gig Harbor
Country: United States
Vessel Name: Kinship
Vessel Model: North Pacific 43
Join Date: May 2015
Posts: 2,786
Thanks again TT. That was a simple enough explanation that even I understood it.
__________________
Regards,

Dave
SPOT page
dhays is offline   Reply With Quote
Old 07-28-2016, 05:52 PM   #35
Guru
 
Insequent's Avatar
 
City: Brisbane River
Country: Australia
Vessel Name: Insequent
Vessel Model: Ocean Alexander 50 Mk I
Join Date: Mar 2012
Posts: 1,027
Quote:
Originally Posted by twistedtree View Post
Insequent - I'm envious of your solar setup. I sure wish I could get that many panels on my boat.

You may have already done this, but you might be able to take advantage of having two charge controllers. If you have some panels that are more subject to shading than others, try grouping the panels subject to shading on one controller, and the panels not subject to shading on the other controller. Then shading will only confuse one controller while the other can keep cranking away with stable sunlight.
With my old panels I did group them according to shade potential. I estimated that the ones that could get shading at times of the day produced about 60% of what the others did. It wasn't exact as I had 4 un-shaded panels on one controller and 3 potentially shaded panels on the other controller. I 'normalised' to a per panel output to get the 60% estimate. And they were not shaded all that much either.

Sorry I can't be more specific on how much shade and for how long. It was more of a problem in mornings and afternoon. In the most productive part of the day they were usually not shaded, but it did depend on what heading the bow had while at anchor as well.
__________________
Brian
Insequent is offline   Reply With Quote
Old 07-28-2016, 06:30 PM   #36
Guru
 
twistedtree's Avatar
 
City: Gloucester, MA
Country: USA
Join Date: Jan 2013
Posts: 2,304
You may have heard the saying... There is a simple answer to every complex problem, and it's wrong.

For most people building a solar system today, series wired panels will be most shade resistant. Shading of any kind will still be a big issue, but on boats it's nearly impossible to completely avoid. I think the key criteria for series wiring to be preferable are:

1) use of an MPPT controller

2) series wired panels with the highest voltage supported by the controller. The higher the voltage, the more shading the system can tolerate. As soon as the voltage drops below around 110% to 120% of the battery charge voltage, output will drop to zero.

If you don't use an MPPT controller, then parallel wiring is your only option. Older systems are pretty much all like this. But newer panels are generally much higher voltage so an MPPT controller is mandatory or you will end up wasting a huge amount of power because the panels will operate at battery voltage, not their max output voltage.
__________________

__________________
www.MVTanglewood.com
twistedtree is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





All times are GMT -5. The time now is 06:56 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012