5 watt solar panel

sailingdog · May 6, 2009

Louis—

I would recommend you read this primer on solar power on boats I wrote a while back.

I would recommend using a larger panel and getting a small charge controller for it. The charge controller will take care of the discharge at night problem and help prevent the panel from frying your batteries.

The reason I recommend a larger panel, like their 25 watt panel, rather than the 5 watt panel, is the 5 watt panel is barely enough to keep up with the self discharge on a wet cell battery bank, much less re-charge it.

A few questions:

1) How big is the battery bank on your boat?
2) How far down do you bring it over the course of a weekend?
3) Is this the only form of re-charging you're going to be using???

Hermit Scott · May 6, 2009

You can buy a coleman from walmart for less money and the panel is half the size of the harbor freight.

sailingdog · May 7, 2009

HS—

You got a link to the coleman???

Ken Honeycutt · May 7, 2009

Link to WMart panel

sailingdog said:
HS—

You got a link to the coleman???

I've been looking at small panels myself for the same purpose of topping off the batteries during the week when I'm away from the boat. Here's a link to the WallMart panel.

http://www.google.com/products?q=coleman+solar+panel&authorid=1113342&cdn=Wal-Mart&lnk=storesugg

Looks like they've got 2 sizes.

sailingdog · May 7, 2009

Depending on your battery bank size and composition, those may keep the batteries topped off, but won't do much in the way of recharging them. A wet cell battery bank can lose almost 1% of its charge just sitting there on a hot summer day. A nine watt panel will put about 3 amp-hours back into the bank. If you have a single 100 amp-hour battery, this might be sufficient to bring it up a bit over the course of a week, but a larger panel would make sense for most people, especially if you have any parasitic loads, like a bilge pump on the batteries.

Ken Honeycutt said:
I've been looking at small panels myself for the same purpose of topping off the batteries during the week when I'm away from the boat. Here's a link to the WallMart panel.

http://www.google.com/products?q=coleman+solar+panel&authorid=1113342&cdn=Wal-Mart&lnk=storesugg

Looks like they've got 2 sizes.

Ross · May 7, 2009

Some German car makers use a small solar panel to keep the car batteries charged during shipment and storage. But I think that you would need the equivilant of one for each battery just to hold what you have. You would need more to show any significant gain.

som1335 · May 7, 2009

For the same money as HF you can get a 5 watt with built in overcharge and reverse current protector. $50 should buy you a decent 1. I find that a 5 watt works great for your situation. had 1 on my Mac and stink boat and never had an isssue. Put 1 on my new boat too. won't revive a dead battery any time soon, but great for keeping them topped off. i leave my fridge on all week and the battery lasts with a 5 watt attached. pretty low, but not dead. I live in the northeast so fridge doesn't run a lot at 58 degree water around it.

Ross · May 7, 2009

The solar panels that come with the cars are sold on Ebay.

Bad Obsession · May 8, 2009

If you keep it at a dock, why not use shore power to charge your batteries?

Ken Honeycutt · May 8, 2009

Folding Solar Panels

sailingdog said:
Depending on your battery bank size and composition, those may keep the batteries topped off, but won't do much in the way of recharging them. A wet cell battery bank can lose almost 1% of its charge just sitting there on a hot summer day. A nine watt panel will put about 3 amp-hours back into the bank. If you have a single 100 amp-hour battery, this might be sufficient to bring it up a bit over the course of a week, but a larger panel would make sense for most people, especially if you have any parasitic loads, like a bilge pump on the batteries.

Ideally I'd like one of those folding panels. Found a couple 25 watt ones on the web but:
a) they're not cheap
b) most of them had to be ordered from overseas.

Wish I could keep the fridge cool during the week while away. Not sure how a 5 watt panel would do it. Had an 80 watt panel on my last boat plus a wind generator and it barely kept up. Probably had something to do with the insulation though. Nice to have that cool one right away!

som1335 · May 8, 2009

Louis said:
Thanks for all the replys and information. I've been away and haven't been able to check in. My needs are very basic. I have one battery and literally just use the radio & finder for a couple of hours on the weekend. I think the 5 watt would fill the bill nicely. Som1335, what panel are you referring to. That one sounds really good. BTW are you on the Hudson too?

I'm in Penobscot bay Maine. I don't remember where I got mine but in the fine description you should look for a unit designed to not allow reverse current (simple diode). The electronic control also will prevent overcharging whcih is a very remote possibility with a 5 watt and a full sized battery, but none the less nice feature.

Ron20324 · May 8, 2009

Louis, to answer your question, yes you need a diode unless you disconnect the wires when there's not enough sun for a charge. West has said diodes rated 45 volts, 8 amps, 2 for $16. As usual, you can get the same things at Radio Shack for alot less. You want 35 volts or more rating, but 5 watts at 12 volts is not the 8 amps, so you could get by with a smaller amperage. Amperage never hurts though- in a diode, that is.

"The book" says if the panel current is less than .5 percent of battery capacity (1 amps for 200Ah battery), you don't need a charge controller. It sounds like you don't need one.

sailingdog · May 9, 2009

The problem with using a blocking diode for a solar panel this size is you're going to lose much of the charging potential...a blocking diode costs you almost 1 Volt of potential when used...

If the OP's goal is to trickle charge the batteries, presumably so that over the course of a week, he puts back what he used up over the previous weekend, he's going to need more than a 5 watt panel. A five watt panel is a battery maintainer, but will do very little in the way of recharging the battery. He's not going to see much in the way of recharging until he gets up to a 25 watt panel or so.

You can get a small, <4.5 amp, solar charge controller for as little as $29... which makes a lot more sense than using a blocking diode. It will do a far better job of protecting the battery as well as control the voltage output, and isn't much more in terms of cost.

RogerHM · May 11, 2009

Hi Louis, IMO, for your needs/wants the 5W will do You. I used a similar bought from Canadian Tire--that's in Canada, eh--with its own over-load control and worked fine.
I now have a second one attached to my one deep-cycle cuz I'm on the boat throughout the week with a lap-top on which I play the odd DVD on long nights...
Try one. You can always add another/more...
Run a frig all week to have a cold-one??? :-0 YIKES!!

Roger

Ron20324 · May 11, 2009

[http://www.batterystuff.com/solar-chargers/SCC015.html

som1335 · May 12, 2009

Ok no-one believes the whole week thing. Look at it this way. 58 degree water, fridge set to warmest level it cycles only about once every 3 to 4 hours if well insulated. I have another 12 volt cooler that will take down a battery in 4 hours so equipment and temp are key. I understand the techs of this, my EE son had doubts too, but its amazing how little a good frige (small) runs when the door isn't opened. try it at home in the early spring or late fall.