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Catalina/Capri 25/250 Sailor's Forums

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Solar Panel Charging

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CB
1st Mate

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54 Posts

Initially Posted - 11/25/2003 : 09:19:47

Will a 5-watt solar panel keep one battery maintained for the following scenario?
-I use the boat primarily for daysailing, 4-6 times a month, a few overnighters per season. I run a CD player/radio mostly, and basic electronics (depth, wind speed/direction indicator, & knotmeter).
My engine does NOT have an alternator or electric start.

The panel I purchased says it has a "blocking diode to prevent reverse charging", and it's "zero maintenance".
So, can I just leave it hooked up in between sails at the dock and not worry about it?
Thanks in advance for your input,
Chris
#2672 SR/SK Deez Knots, Lk Norman, NC

Edited by - on

ClamBeach
Master Marine Consultant

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3072 Posts

Response Posted - 11/25/2003 : 10:11:36

Well, you could do some thumbnail calculations to get a rough 'energy budget'.

At your full 100% rated output in direct sunlight, you get 5 watts from your panel.
5 watts @ 12 Volts = about 4/10 of an amp.

Allowing for shading, bad sun angle, cloudy day etc.. let's assume you get the equivalent of 10 hours full output from a "typical" summer day. That's about 4 amp-hours per day.

If you sail every 5 days, that's approx 20 amp-hours per recharge interval.
(Note: you will get some natural battery charge loss during the nighttime intervals, but for our purposes here I'll just discard it.)

Look at the owners manual for your instruments and cd player and get the power consumption. Multiply the power consumption in amps times the hours you have the electronics on and you'll get your drawdown.

My own guesstimate is that you'll be at just about a break-even on your energy budget. (Summertime) With winter sunlight hours, it may not keep up.

4/10 of an amp is down in the lower end of 'trickle charge' range.
I don't think it will boil your battery unless you left it on a very long time unattended.

Edited by - on

Mark Loyacano
Navigator

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USA
247 Posts

Response Posted - 11/25/2003 : 10:47:58

CB, my 5 watt solar panel has done a great job all Summer. I occasionally hook up an electrical charger to verify that all is well. It runs less than a minute before switching to float charge.
The fewer daylight hours available during Winter may make a difference. I'm not sure yet.

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CB
1st Mate

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54 Posts

Response Posted - 11/25/2003 : 11:41:17

Thanks for the info, if anybody needs a 5-watt panel, I picked it up yesterday on a whim when I was in Harbor Freight Tools. It was on sale for $34.99 or something like that.
It may be a P.O.S., but it was cheap, we shall see if it does the trick.
Chris

Edited by - on

eric.werkowitz
Captain

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USA
283 Posts

Response Posted - 11/25/2003 : 19:26:49

Chris,

Make sure that solar panel is rated for outside use. Many of those Harbor Freight panels are intended to be used on the dash board of a car or RV where they are protected by the windshield from rain and weather.

If it's an "inside" model you could probably build a weather tight enclosure with some wood, silicone caulk and glass.

Eric Werkowitz
C25 #4969

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Todd Frye
Navigator

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USA
222 Posts

Response Posted - 11/26/2003 : 18:08:54

When I'm using battery power on board, I like to keep an eye on my voltmeter. If it gets cloudy and appears to be staying that way, I will back off on the toys (CD player, auto pilot, GPS) if my read out drops below 12.5 volts. My max readings from my 5amp solar panel have been consistent 13.75 volts and don't seem to drop in full sun, with the above-mentioned devices at work. Todd Frye

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Gloss
Master Marine Consultant

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USA
1916 Posts

Response Posted - 11/26/2003 : 22:24:50

Hi there, and a happy turkey to everyone,
I recently did some studying on solar power. There are charts which show the amount of usable sun you should figure in your calculations, based on location, and latitude. For Knoxville, I believe it is about 6 or 7 hours, Very few places had 10 hours. You also have to figure out that you won't get all of the energy as you will not be perfectly aimed all the time.
I have an 11 watt flexible Uni solar panel, and a digital charge controller which also has a digital readout of the amps which I am drawing off my system, how many amps my panel is putting out, and battery voltage. (I'm a sucker for gadgets)
My 11 watt panel will only top out at .6 amps on a sunny day with great panel alignment.
My cabin top exhaust fan draws .1 amp, the CD player .6 amp.
Lights really suck up the amps.
Hope that this helps.

Edited by - on

deastburn
Captain

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USA
334 Posts

Response Posted - 11/29/2003 : 18:30:52

I have recently purchased a small solar panel to use on my car when skiing. The idea is to give a bit of a boost to the battery when the temp drops below -20.

I have a question I am sure you electrical geniuses can answer, and the same question applies to using the panel on my boat:

When I turn the ignition off, the twelve-volt cigar lighter plug on my car switches off, so I would assume the solar panel will not charge the battery in this condition. If I leave the ignition on, even with all accessories switched off, the drain (from idiot lights etc.) will still exceed the charge. What to do?

Likewise with my boat. In order to charge the batteries through the twelve volt power take-off, the batteries --or at least one of them--has to be left on. Would not that increase the drain, even with no accessories switched on?

This is a request from help from a sailor who doesn't know his amps from his volts from his watts.

Edited by - on

eric.werkowitz
Captain

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USA
283 Posts

Response Posted - 11/29/2003 : 23:48:23

Dave,

You're right about the cigarette lighter. If it is not "live" when the key is off, then the charger isn't going to charge through it. You could run a couple wires from the battery to a separate "lighter" receptacle and stick it in your glove box or something. Be sure to put an in-line fuse in the line from the positive terminal as close as possible to the battery in case the wire shorts or something.

In regards to the other question, if no other accessories are on the line that goes to the cigarette lighter, there is nothing to "drain." Of course most of the switches have a light to indicate that the switch is on. That light will cause a drain.

You can do the same thing I suggested for your car, only doing it on the boat will be much easier.

Eric Werkowitz
C25 #4969

Edited by - on

deastburn
Captain

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USA
334 Posts

Response Posted - 12/01/2003 : 17:59:41

Thanks, Eric. A project for the Spring, when things begin to warm up...

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rwall10597
Deckhand

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USA
11 Posts

Response Posted - 12/12/2003 : 01:07:16

I bought a 5 Watt flexible panel over the summer, I have not had to put any other charger on my battery since. I bought a voltage meter and I check the battery most every time I am at the boat, it is always right around 13 volts. I mounted the panel on the forward hatch; it actually makes the boat look really sharp. By the time I took the hatch off, mounted the panel, drilled and sealed a hole for the wire, put the hatch back on, then ran the wire down into the bilge and back to the battery compartment, it ended up taking about half a day.

Several of the boats on my dock have rail mounted rigid panels. This seems like a hazard to me, catching a sheet on it, or hitting it with something and cracking the glass. A few other folks have flexible panels that are not mounted that they put out on deck when they leave the boat. I don’t recall seeing any other permanently mounted flexible panels, but I highly recommend it. I wish I had done it sooner.

BW

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RichardG
Admiral

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USA
990 Posts

Response Posted - 12/12/2003 : 13:19:27

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">I bought a 5 Watt flexible panel over the summer<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

Bob:

Where did you get it? How much was it?

Where's the best deal for one of these (assuming not WM)?

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coach
Navigator

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USA
231 Posts

Response Posted - 12/12/2003 : 14:15:47

We have a solar panel for our 25 and we use it to charge two batteries and we never run into a problem. It should do the job
for you.

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