Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 31-07-2015, 16:13   #1
Registered User

Join Date: Sep 2013
Location: Alert Bay, Vancouver Island
Boat: 35ft classic ketch/yawl.
Posts: 931
Images: 4
Send a message via Skype™ to roland stockham
Sizing small solar panels for batt storage

Hi all. Need advice on size of solar panels. I am leaving the boat on hard standing for 6-9months and there is no electric available. In the Carribean so lots of sun. I don't have anywhere to put large panels so a full setup is out.
What would be the right size panel to keep 700Ah of lead acids up. No loads running but how much extra would you reckon the run the bilge pumps on a 35ft?
I have a little 5watt panel but that will only run a radio or GPS, gives about 150ma. I think I need 2-3a @13.4v, that's about what the charger runs at when everything is charged which is 25-40W. But, given that the 5W panel actually on produces about 2W I am a bit stuck on sizing! Don't want to overdo it and cook the batteries.

Thanks
__________________

__________________
roland stockham is offline   Reply With Quote
Old 31-07-2015, 18:15   #2
Registered User

Join Date: Jun 2009
Location: still in a roll of fiberglass around Cape Town
Boat: Leopard 40 (new model)
Posts: 1,201
Re: Sizing small solar panels for batt storage

Quote:
Originally Posted by roland stockham View Post
Hi all. Need advice on size of solar panels. I am leaving the boat on hard standing for 6-9months and there is no electric available. In the Carribean so lots of sun. I don't have anywhere to put large panels so a full setup is out.
What would be the right size panel to keep 700Ah of lead acids up. No loads running but how much extra would you reckon the run the bilge pumps on a 35ft?
I have a little 5watt panel but that will only run a radio or GPS, gives about 150ma. I think I need 2-3a @13.4v, that's about what the charger runs at when everything is charged which is 25-40W. But, given that the 5W panel actually on produces about 2W I am a bit stuck on sizing! Don't want to overdo it and cook the batteries.

Thanks
When you say "lead acid", do you mean flooded (as opposed to AGM lead acids?)

Are you talking about panels connected directly to the battery, without a controller/regulator in between?

If so, ask your battery manufacturer. The panel will need to offset the self discharge, which is significant for flooded batteries and depends on the composition of the plates (antimony vs calcium). I estimate you will need in the order of one amp times 12 hours a day just to offset self discharge.

You can make your own estimate by first charging the batteries to 100% (ie when accepted amps at manufacturer-specified absorption voltage drop to manufacturer specified value, say 1or 2% of 700 = 7 to 14 amps. Then use a shorepower charger to keep the batteries at float voltage and measure the amps going in to the batteries. Multiply those amps by 13 or so and get the rating in W of the panel you want.

All that said, given that these days you can get a proper Victron solar controller for US$105, there is no need to walk the fine line between undercharging and overcharging the batteries by not having a controller.
__________________

__________________
svlamorocha is offline   Reply With Quote
Old 01-08-2015, 09:42   #3
Registered User

Join Date: Sep 2013
Location: Alert Bay, Vancouver Island
Boat: 35ft classic ketch/yawl.
Posts: 931
Images: 4
Send a message via Skype™ to roland stockham
Re: Sizing small solar panels for batt storage

Thanks for that and yest they are flooded deep cycle. I have measured the charge going in from the shore charger and it is about 20Ah/day which suggest a panel output of 3A for 6 hrs or about 40w. I was hoping to find someone who has used small panels like this and find out what thy got in real life. don't want to buy something and find the output is half what I expect. The ideal would be something I can temporarily hook up whenever I leave the boat.
__________________
roland stockham is offline   Reply With Quote
Old 01-08-2015, 10:40   #4
Senior Cruiser

Cruisers Forum Supporter

Join Date: Mar 2007
Location: Santa Cruz
Boat: Boatless Again
Posts: 4,310
Re: Sizing small solar panels for batt storage

If you have room for 50 watts, just add a $10 regulator from Ebay and fugettaboutit.
__________________
donradcliffe is online now   Reply With Quote
Old 01-08-2015, 11:20   #5
֍֎֍֎֍֎֍֎֍֎

Cruisers Forum Supporter

Join Date: Apr 2006
Posts: 13,022
Re: Sizing small solar panels for batt storage

700Ah of batteries might only need 150-200mAh of charging to offset the normal self-discharge of the batteries. You'd have to check out their specs to find out what those particular batteries need, and then look for a battery "maintainer" rather than a full powered charger, to simply maintain them.


Since you're on the hard, check for a bilge drain plug and consider installing one if it isn't there. No reason to run a bilge pump when you're on the hard, and using a drain plug also means you don't worry about the bilge pump failing, which they regularly do. Or starting a fire. If you must keep the bilge pump...I'd consider putting in a separate unregulated solar panel, just to power the bilge pump. That's not a totally reliable solution, obviously, but it should keep up with any routine seepage, without complicating the battery maintenance.
__________________
hellosailor is offline   Reply With Quote
Old 01-08-2015, 12:14   #6
Hybrid Power Supply
 
Hybrid Power's Avatar

Community Sponsor

Join Date: May 2015
Location: Calgary, Ab
Posts: 34
Send a message via Skype™ to Hybrid Power
Re: Sizing small solar panels for batt storage

A good rule of thumb is for panel sizing is to design a setup that will yield at least 3A (Imp) per 100 amp-hours of battery capacity.

For small panels of less than 140 watts you cannot go wrong with a little Genasun controller.
__________________
We supply cruisers with premier off-grid power systems.

Hybrid Power is offline   Reply With Quote
Reply

Tags
panels, solar, solar panels, storage

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


Similar Threads
Thread Thread Starter Forum Replies Last Post
Solar panel Installation and wire sizing from the solar panels to the mppt charger boatrips Electrical: Batteries, Generators & Solar 17 08-02-2015 19:25
Practical aspect of sizing solar panels? Delancey Marine Electronics 20 17-03-2014 00:36
Solar panels - sizing wiring for voltage drop galacticair Electrical: Batteries, Generators & Solar 43 01-07-2013 20:09
1 Solar Monitor-Marine Switch-2 Batt Banks on RV! aztecaa Electrical: Batteries, Generators & Solar 0 06-06-2012 11:33
Wire Sizing for Installing Solar Panels / Wind Generator Eddie Electrical: Batteries, Generators & Solar 17 30-03-2010 20:06



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 12:01.


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.