solar

Aug 10, 2020
511
Catalina C25 3559 Rocky Mount
I new to solar. I am wanting a solar panel to keep my battery up. I only plan on running one battery on my 26 laguna. The only things running off the battery with be a depth finder, cabin lights, nav lights, bilge pump and to start the outboard. All lighting is led. Will a 50W panel and controller keep up? should I buy more than I need and go 100W? I was looking at a kit from "renogy". Do they make a decent product? Most of the time the only thing that will be on is the depth finder.

Thank in advance .
 
Jan 11, 2014
11,321
Sabre 362 113 Fair Haven, NY
100 watt will be better. The 50 watt panels will keep a charged battery charged but can't charge a battery that is discharged.

Also, there 2 types of chargers, an MMPT and PWM. You want the MMPT charger as they are more efficient.

Buy from a reliable source, the solar market is like the Wild West with lots of misrepresented products. Alt E is a good source of reasonably priced panels of decent quality. They also have a lot of educational materials.

 
Jun 14, 2010
2,081
Robertson & Caine 2017 Leopard 40 CT
For what he wants to charge, the 50w panel should be adequate to keep it topped up between uses. It might not be enough to keep it charged with all electronics in use (and depending on how much light) but that's not what this is about:
1) establish a daily"power budget" by measuring the total consumption (in amps) with an ammeter with all devices in use. Then estimate how many hours per day they will likely be in use. Total amps x hours in use = amp-hours daily budget. (Disregard the outboard starter, see note 4 below).
2) Size the solar panel by the number of watts. Watts/volts = Amps. This is a very inexact science because the real world is far from ideal conditions. Divide the amount derived from the spec by two because you'll only get the rated spec on a clear day at noon at the equator. Then assume 8 hours per day of full sunlight (yes, generally more in summer, but not full sunlight, and even less in overcast conditions). 8 x number of amps = amp-hours estimated from solar (more or less).
3) You don't need to generate enough power to exceed your daily power budget if you don't use the boat every day. If you won't use the boat every day, think of the maximum number of consecutive days you will use the boat, and establish a power budget that allows a daily deficit to deplete the battery to 60% charge (based on the battery capacity rating in amp-hours) over the course of that number of days. (Don't draw your battery down more than 50% for maximum life) You don't need to be back to 100% every day, but at the end of that period you will need to allow the boat to recharge while sitting "n" number of days.
4) Your outboard probably has a 4 or 6 amp alternator. Assume the alternator can recharge the battery at a rate about half its rated charge power. If you motor for extended periods you can factor that in. If not, I'd ignore it and view it as bonus power. At any rate, it will probably put enough power back into the battery to negate the amount it draws during start. The start current is high but it's only used for a very short duration.
 
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Aug 10, 2020
511
Catalina C25 3559 Rocky Mount
I was just reading a post that said that nearly word for word. I believe regarding a farrier 24. I like the formula.
 
Mar 26, 2011
3,399
Corsair F-24 MK I Deale, MD
50 watts is plenty. My boat is very similar and I have had this system for 5 years. Very simple and compact. Yes, it will take 2-4 days to recharge a low battery, depending on how flat it is. But if all you are doing is day sailing with the occasional over night, the battery will never get low.
Super Simple Solar


I had a much larger and more complex system (240W) on my cruising boat. Whole different animal. That boat had more lighting, refrigeration, hot water, TV and DVD, propane, AC, and 3 large batteries. Different.
 
Aug 10, 2020
511
Catalina C25 3559 Rocky Mount
50 watts is plenty. My boat is very similar and I have had this system for 5 years. Very simple and compact. Yes, it will take 2-4 days to recharge a low battery, depending on how flat it is. But if all you are doing is day sailing with the occasional over night, the battery will never get low.
Super Simple Solar


I had a much larger and more complex system (240W) on my cruising boat. Whole different animal. That boat had more lighting, refrigeration, hot water, TV and DVD, propane, AC, and 3 large batteries. Different.
thank you
 
Sep 8, 2020
48
Merit 22 Honker Bay
I have a 30W panel and a PWM controller and have no problem powering my autohelm and radio all day. My battery drops maybe 1/4volt after a day of sailing. I haven't used my nav lights. But I'm changing them to LED's so I don't expect any power problem.

An MPPT would be more efficient. But the PWM controller was in my electrical junk box. I also believe PWM controllers suffer less from partial shading than do MPPT's.
 
Feb 8, 2014
1,300
Columbia 36 Muskegon
I have a 30W panel and a PWM controller and have no problem powering my autohelm and radio all day. My battery drops maybe 1/4volt after a day of sailing. I haven't used my nav lights. But I'm changing them to LED's so I don't expect any power problem.

An MPPT would be more efficient. But the PWM controller was in my electrical junk box. I also believe PWM controllers suffer less from partial shading than do MPPT's.
When I jumped into solar I didn't do enough research, and ended getting a 24V panel and PWM controller to charge a 12V battery. It didn't work. I should have gotten up to 10 amps out of the panel but only saw 1 or 2. I upgraded to an MPPT controller and immediately started getting 9 and 10 amps. That's what MPPT does, it takes all advantage possible from the array. Pretty much essential if your panels are connected in series or mismatched. With just one panel matched to the battery, MPPT is not as essential but still more efficient. They're not that much more expensive these days.
 
Jun 14, 2010
2,081
Robertson & Caine 2017 Leopard 40 CT
ended getting a 24V panel and PWM controller to charge a 12V battery. It didn't work.
The dramatic difference you saw is not from PWM vs. MPPT. It was a simple misconfiguration / mismatch. Likely damage to the PWM controller or perhaps limiting from its protective circuits from an overvoltage input. If you had a 12v panel you would not see much difference between PWM and MPPT, perhaps 5-15% depending on real-world conditions.
MPPT can do the voltage conversion required by your 24v panels to step down to a 12v battery.