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Solar chargers

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hhh
Deckhand

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10 Posts

Initially Posted - 06/03/2006 : 14:36:38

Wondering if a 350mA solar panal will do much good if left on the battery during the week.(cenrtal Missouri) We don't use the battery very much just for a water pump and night lights once in a while. The only other charge the battery gets is when we run the outboard which is very litte and when we lug the battery home. Wondering if this would keep it charged so we would not have to bring battery home a couple times a year or if it is just better to bring it home and not have another piece of equipment onboard that someone could steal when boat is in the slip? hhh

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OLarryR
Master Marine Consultant

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USA
3467 Posts

Response Posted - 06/03/2006 : 17:39:57

A 350mA solar panel is about 5 watts. On various solar panel websites (ie. Norhtern Arizona Wind & Sun, http://store.solar-electric.com/1to39wasopa.html), they indicate that a panel of that size does not require a controller. But...there is more to this as follows:

A 12 volt battery will discharge a bit each day. They lose a little less than
1 amp/day in the winter and perhaps .5A/day in the summer. So....charging at the capacity rating of your panel would be .35A/Hr but....rarely do the panels put out the max unless the panel is perfectly perpendicular to the suns rays during the day and nothing blocks the panel throughout the day. It is much more common to get only about 1/2 - 3/4 of the capacity rating at any one time during the day and then there is clouds some days, etc. Taking all that into account, you are probably getting an average of .2A/hr and probably only for about 6 hrs max each day and that is on mostly all sunny days. That gives you as max of .2 X 6 = 1.2A/day. Then figure some days are cloudy or raining and some days you are using your boat and doing addl discharging. So....you are just above or equal to the daily discharge rate of the battery. But there is another factor.....during the night-time, without a controller/blocking diode, the solar panel w/wires hooked to the battery actually let's some of the juice back out. Not exactly sure what the process is called but some minute amount escapes thru the night.

So.....between the low amp charging, not under always ideal conditions, some slight night-time discharging, ther battery losing some charge daily....you break about even. If you were charging the battery above the trickle lost each day, then depending on how much above, you would then have to get a solar controller to keep the water in the battery from cooking off. Recommend check your battery every so often if it is a flooded one and allows you to look at the water level. There will be some water that is naturally lost and will have to be replaced but you should with time gain confidence that the 350ma panel is not cooking the water off at a fast rate or at all.

(My website shows my 20Watt panel arrangement with a solar controller.)

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OLarryR
Master Marine Consultant

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USA
3467 Posts

Response Posted - 06/03/2006 : 17:47:40

Actually, I did not really answer your question - Should you leave the panel on the boat. I would say - definitely ! People buy solar panels so they will not have to replace batteries that often. Your panel is not very large and so maybe makes it more prone to stealing....but at only say 5 watts....not even worth stealing and it isn't such a big investment anyway. My experiences have been that most people passing my finger slip on the way down the dock to their boat are oblivious to my 20 Watt panel hanging up above my outboard motor. Chances are smae will be true with your panel. Most won't even notice it.

The primary time the solar panel does it's job is when we are not on the boat. That is on most weekdays. Keep it on !

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lcharlot
Master Marine Consultant

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Antigua and Barbuda
1301 Posts

Response Posted - 06/04/2006 : 23:10:31

A 5 watt panel isn't really enough power to recharge a battery that has lost some charge during a day of useage of boat electronics, but's it's enough to keep a full battery topped off, at least in the summer months. For the electrical loads of an average weekend of sailing, including cabin and navigation lights in the evening, stereo, depth sounder, and GPS, A 30 watt panel is probably the minimum you need to recharge the battery during the 5 week days following a weekend on the boat. For an extended cruise, like a two week vacation, I would want a 50 watt panel, or perhaps even two, and I would want two batteries in the house bank, at least one a Group 27. If your battery box is big enough for two Group 27's, that's what I would go with.

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Stu Jackson C34
Admiral

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844 Posts

Response Posted - 06/05/2006 : 12:26:44

hhh

We had an 11 watt solar panel on our C25 to keep up the battery. We located it in the cockpit, and locked it with one of the grommets going through the hasp on the port locker. A bungee cord ran across the cockpit to keep it horizontal. It was out of the way and out of sight and locked, but because of how our slip was arranged, got plenty of sun.

A good reference is: http://www.westmarine.com/webapp/wcs/stores/servlet/westadvisor/10001/-1/10001/solarpanels.htm

The West Marine Advisors also include an energy budget form, which you should do so you'll know how much you are using and how much you need to put back. http://www.westmarine.com/pdf/Elecbugt.pdf

I'm sure our solar panel extended the life of our single 95ah gel cell for many years -- it lasted over 5 years. Because the panel's output was less than 1-1/2% of the total battery capacity in amp hours, no regulation was required. We charged it occasionally with an automotive charger, which was the wrong thing to do. Gel cells won't work with auto chargers which put out either too little or too much voltage - but battery charging is another topic (which is also well covered in the West Advisors).

There are a lot of other solar panel resources out there, including emarine (try http://www.e-marine-inc.com/products/solar_panels/solar_panel.html).

Solar is a great idea for your application.

Edited by - Stu Jackson C34 on 06/05/2006 12:32:09

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The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.