Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 31-01-2014, 11:20   #1
Registered User
 
autumnbreeze27's Avatar

Join Date: Apr 2012
Location: Cruising Mexico
Boat: 50' Herreshoff Ketch
Posts: 967
Solar panels that will be partially shaded--which is better?

I want to put solar panels on the top of my dodger. I've got about 4'x4' on each side of the boom when it's centerlined (total space is about 9' wide by 4'). My goal is near 500w of solar on the dodger top (if possible) so as to not spoil her lines and shade the dodger.

So the problem I'm having is most panels are somewhat over 5' long, which means they'll have to hang over the cockpit (if they hang over forward they'll hit the rigid boom vang)

Now I know I'm going to have shading issues in this location, (rigging/mast/possibly boom), what gives you better performance in partially shaded panel conditions, 1 big panel or multiple small panels?
__________________

__________________
autumnbreeze27 is offline   Reply With Quote
Old 31-01-2014, 11:50   #2
Marine Service Provider
 
Emmalina's Avatar

Join Date: Jan 2012
Location: Thailand
Boat: Herreshoff Caribbean 50
Posts: 482
Re: Solar panels that will be partially shaded--which is better?

Removed my dodger and put a hard top and 1100w solar on there using semi flexible panels Also have a gallows on there and rain catching ability... Never looked back... semi flexible panels come in all shapes and sizes. Look em up on the net. Shading will always be an issue... Just calculate 50% output as a ball park figure.
__________________

__________________
Steve .. It was the last one that did this !
Emmalina is offline   Reply With Quote
Old 31-01-2014, 13:54   #3
Registered User
 
sparrowhawk1's Avatar

Join Date: Jan 2014
Location: Miami Beach Fl
Boat: Colombia Cc 11.8
Posts: 1,252
Quote:
Originally Posted by autumnbreeze27 View Post
I want to put solar panels on the top of my dodger. I've got about 4'x4' on each side of the boom when it's centerlined (total space is about 9' wide by 4'). My goal is near 500w of solar on the dodger top (if possible) so as to not spoil her lines and shade the dodger.

So the problem I'm having is most panels are somewhat over 5' long, which means they'll have to hang over the cockpit (if they hang over forward they'll hit the rigid boom vang)

Now I know I'm going to have shading issues in this location, (rigging/mast/possibly boom), what gives you better performance in partially shaded panel conditions, 1 big panel or multiple small panels?
Most of the time large panels are actually smaller panels in parallel. For 12 volts nominal basically 17.5v charging it takes 36 cells. For shading you're better off with more sets of 36 because even if two or three cells in that panel are shaded voltage will drop severly limiting charging amprage . If the panels are smaller then the total percentage lost is less. A question I have, when you have a mppt contoller is 24 volt or 12 volt more shade tolerant
__________________
sparrowhawk1 is offline   Reply With Quote
Old 31-01-2014, 14:07   #4
Registered User
 
sparrowhawk1's Avatar

Join Date: Jan 2014
Location: Miami Beach Fl
Boat: Colombia Cc 11.8
Posts: 1,252
Click image for larger version

Name:	ForumRunner_20140131_160423.jpg
Views:	233
Size:	140.8 KB
ID:	75050

This is one of my large panels, its actually two smaller panels in parallel. It's also very important to have the panels running fore-and-aft that way the shadows are more likely to fall on one panel
it's usually less expensive to buy the bigger panel than it would be to buy two smaller ones and it's effectively the same thing. I should probably rewrite this. bottom line is more groups of 36 are better but it doesn't matter if the're grouped in one frame. sorry for my confusing Explanation.
__________________
sparrowhawk1 is offline   Reply With Quote
Old 31-01-2014, 14:56   #5
֍֎֍֎֍֎֍֎֍֎

Cruisers Forum Supporter

Join Date: Apr 2006
Posts: 13,037
Re: Solar panels that will be partially shaded--which is better?

"1 big panel or multiple small panels?"
One big panel, if shaded, gets knocked out. Multiple small panels, if laid out so that they checkerboard the shade, means you may have 1 panel knocked out and 3 working 100%. So I'd look at the options for putting in 4-6 smaller panels, see if that would allow you to keep at least half of them fully in the sunlight on each tack.

And if one big panel takes any kind of damage, even water damage, it is out. Multiple smaller panels gives you some redundancy against that, too.
__________________
hellosailor is offline   Reply With Quote
Old 31-01-2014, 15:48   #6
Moderator
 
noelex 77's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Location: Living on dirt waiting for our new yacht to be built.
Boat: Half built Bestevaer.
Posts: 10,619
Re: Solar panels that will be partially shaded--which is better?

Multiple small panels do better than a fewer number of large panels in conditions where there are patches of isolated deep shade (such as from a boom).

However, small panels take up more room for the same wattage due to the wasted area around the frame. In addition manufacturers do not offer many high efficiency panels in the smaller sizes.

Large panels with more than 36 cells are usually wired in series (although not always as Sparrowhawk reports). These don't do much better than 36 cell panels in terms of shade performance. (This does depend on what other panels are connected where the shadows are falling etc)

In general the most important factor is fit the most watts you can in the least shaded areas with the easiest mounting, most durable and aesthetic result for the lowest cost. Sometimes these goals are easier to achieve with multiple small panels in other installations a few larger panels are better. If all other things are equal multiple small panels will give a slightly higher output, but usually other factors are more important.

When comparing large and small rigid panels make sure to include the shipping cost in your calculations. Some couriers charge a hefty premium for large panels of glass. This can be a significant cost and make multiple small panels a more attractive option. This difference is not always obvious when comparing web prices as shipping cost is not calculated until you confirm the order. Large panels are often higher voltage which reduces the wiring cost, but does mean you can only use a MPPT controller.
__________________
noelex 77 is offline   Reply With Quote
Old 01-02-2014, 10:17   #7
Registered User

Join Date: Oct 2010
Location: Oregon
Boat: 57' Laurent Giles Yawl
Posts: 755
Re: Solar panels that will be partially shaded--which is better?

How much does a thin shadow from rigging affect output?

We would like to add panels on top of our bimini, but have a split backstay that will throw a thin line shadow across the panels all day..

Does anyone have experience with an installation like this?
__________________
our blog
msponer is offline   Reply With Quote
Old 01-02-2014, 10:46   #8
Registered User
 
sparrowhawk1's Avatar

Join Date: Jan 2014
Location: Miami Beach Fl
Boat: Colombia Cc 11.8
Posts: 1,252
Quote:
Originally Posted by msponer View Post
How much does a thin shadow from rigging affect output?

We would like to add panels on top of our bimini, but have a split backstay that will throw a thin line shadow across the panels all day..

Does anyone have experience with an installation like this?
My boat's a center cockpit so my back stay is a little farther back. And I also have panels on my davits. Personally I feel that the small effect of shading from your back stay and more importantly the piece of stainless steel where it splits is more than compensated by having your panels in a safe place. But I have found when I'm sailing the panels on the davits rock. The mainsail almost always blocks the panels on my bimini. But that will change when I finally get to the trade winds!
__________________
sparrowhawk1 is offline   Reply With Quote
Old 01-02-2014, 12:22   #9
Registered User

Join Date: Sep 2012
Posts: 4,947
Re: Solar panels that will be partially shaded--which is better?

If my memory serves me well I believe the semi flexible panels do a little better when shaded than the rigid panels do.
__________________
robert sailor is online now   Reply With Quote
Old 02-02-2014, 11:54   #10
Registered User
 
autumnbreeze27's Avatar

Join Date: Apr 2012
Location: Cruising Mexico
Boat: 50' Herreshoff Ketch
Posts: 967
Re: Solar panels that will be partially shaded--which is better?

I still don't have enough info to make a decision, but I'm leaning towards smaller panels.

Mono Panel - Cost more than poly, smaller than poly, lighter than poly, last longest, mature product, better than poly in hot weather, more loss if shaded than poly
Poly panels - Cheaper, lower heat tolerance, lower efficiency so panels are bigger, worse in hot weather, but better if shaded?
Flexible panels - Still researching, but they look EXPENSIVE

and where do you guys buy? Online? Local Solar person?
__________________
autumnbreeze27 is offline   Reply With Quote
Old 02-02-2014, 12:54   #11
Registered User

Join Date: Oct 2007
Location: virginia
Boat: islandpacket
Posts: 1,833
Re: Solar panels that will be partially shaded--which is better?

.[/QUOTE]

Sorry for the hijack. But tell me about your garden. Looks great.

Sent from my SPH-L710 using Cruisers Sailing Forum mobile app
__________________
That derelict boat was another dream for somebody else, don't let it be your nightmare and a waste of your life.
Badsanta is offline   Reply With Quote
Old 02-02-2014, 12:58   #12
Registered User

Join Date: Oct 2007
Location: virginia
Boat: islandpacket
Posts: 1,833
Re: Solar panels that will be partially shaded--which is better?

Quote:
Originally Posted by sparrowhawk1 View Post
Attachment 75050

This is one of my large panels, its actually two smaller panels in parallel. It's also very important to have the panels running fore-and-aft that way the shadows are more likely to fall on one panel
it's usually less expensive to buy the bigger panel than it would be to buy two smaller ones and it's effectively the same thing. I should probably rewrite this. bottom line is more groups of 36 are better but it doesn't matter if the're grouped in one frame. sorry for my confusing Explanation.
Well that didn't work.
Now tell me about your garden.

Sent from my SPH-L710 using Cruisers Sailing Forum mobile app
__________________
That derelict boat was another dream for somebody else, don't let it be your nightmare and a waste of your life.
Badsanta is offline   Reply With Quote
Old 02-02-2014, 13:07   #13
Registered User
 
sparrowhawk1's Avatar

Join Date: Jan 2014
Location: Miami Beach Fl
Boat: Colombia Cc 11.8
Posts: 1,252
Quote:
Originally Posted by Badsanta View Post

Well that didn't work.
Now tell me about your garden.

Sent from my SPH-L710 using Cruisers Sailing Forum mobile app
Search growing food. I have some good photos and an explanation.
__________________
sparrowhawk1 is offline   Reply With Quote
Old 02-02-2014, 13:39   #14
Registered User
 
Nicholson58's Avatar

Join Date: Jan 2011
Location: Live aboard
Boat: Camper & Nicholson58 Ketch - ROXY Traverse City, Michigan No.668283
Posts: 3,466
Images: 83
Re: Solar panels that will be partially shaded--which is better?

I suggest your read Handy Bob Solar HandyBob's Blog Making off grid RV electrical systems work long read but worth it. This will help you get it right the first time.

The flex panels tend to be about 5 to 10 % efficient. Most of the bulk rigid panels are about 10 to 12 % efficient. If you hunt around you can find panels in the 20 to 22% range. They may have high open circuit voltage which will require an MPPT controller. You can use multiple panels so that partial shade doesn't kill the whole array. Panels may need diodes to keep the shaded panel from dropping out the others. Likewise, some panels are made with zones separated by diodes for the same reason. Typical is 3 zone panels. My Sanyos are 20%; 220 watts; 54 VDC open circuit.
__________________
Nicholson58 is offline   Reply With Quote
Old 02-02-2014, 14:16   #15
Senior Cruiser

Cruisers Forum Supporter

Join Date: Jul 2005
Boat: Outbound 44
Posts: 4,580
Re: Solar panels that will be partially shaded--which is better?

Quote:
Originally Posted by Nicholson58 View Post
I suggest your read Handy Bob Solar HandyBob's Blog Making off grid RV electrical systems work long read but worth it. This will help you get it right the first time.

The flex panels tend to be about 5 to 10 % efficient. Most of the bulk rigid panels are about 10 to 12 % efficient. If you hunt around you can find panels in the 20 to 22% range. .......
These flexpanels claim >20% efficiency and are pretty cheap
MX FLEX Solar Panel Sunpower 100Wp-in Solar Cells, Solar Panel from Electrical Equipment & Supplies on Aliexpress.com
__________________

__________________
Paul L
http://svjeorgia.blogspot.com
Paul L is offline   Reply With Quote
Reply

Tags
panels, solar, solar panels

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

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




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 11:04.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.