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Recommendations for a solar battery maintainer

Sep 22, 2019
75
Catalina 22 Portersville
I have a Catalina 22. I have a 12 volt battery that powers for LED cabin lights and to low current air circulating fans. All other navigation lights, etc. have their own D cell batteries. So, I would like to purchase a solar maintainer to keep the marine battery charged since we often camp overnight on the boat during the summer. Any recommendations?
 
Jan 11, 2014
7,847
Sabre 362 113 Fair Haven, NY
The first step is to get a reasonably accurate estimate of your current needs. How many lights, how much current do they use, how long will they be on? How much current does the fan draw?

Once you have those numbers, then you can begin to size your solar charger. A few factors to consider, first it will take more energy to recharge the battery than is drawn out. If you draw out 10 amp hours, you will need to put in 12 or 13 amp hours to recharge the battery (there is a formula to calculate this more accurately, search for Peukert's equation). Next, on average, a good quality solar panel will produce about 3 times the rated capacity each day, for example, a 50 watt panel will produce about 150 watt hours of energy a day.

A 50 watt panel produces about 4 amps at 12 v (Watts = current * voltage), it would then produce about 12 amp hours of charging capacity, barely adequate for the 10 amp draw I used as an example.

A better choice would be a decent quality marine multi-stage charger. For a weekend overnight, there is likely enough power in a Group 24 battery for your needs. When you get back to the dock (or home if trailering) plug the boat in and properly charge the battery.
 
  • Helpful
Likes: AaronD
Jun 29, 2010
1,250
Beneteau First 235 Lake Minnetonka, MN
@Erbardy I think West Marine's website had a great little spreadsheet, looking for it, that helped with determining one's electrical budget. Well theirs is a PDF file. I do have a nice little spreadsheet I can send you if you want it. You basically put in your numbers and the math gets done for you. I would highly recommend going to all LED lighting on and in your boat to save amps. Let me know if you want that spreadsheet and I will send it to you.
 
May 24, 2004
6,795
CC 30 South Florida
How are you charging your battery at present? I think Diochner gave you a very good dissertation on why a shorepower charger would work best. Solar panels are rated on average conducted over a number of days to account for those cloudy days when sunlight is weak. That is the reason why a 50W panel may produce up to 3 times its rated output in a sunny day. Another drawback is the size of the panel, when you consider than in a 22' boat any space is much valuable. In a practical sense the only reason I would consider a solar panel is if I kept the boat in a mooring to avoid having to carry the battery back and forth.
 
Sep 22, 2019
75
Catalina 22 Portersville
How are you charging your battery at present? I think Diochner gave you a very good dissertation on why a shorepower charger would work best. Solar panels are rated on average conducted over a number of days to account for those cloudy days when sunlight is weak. That is the reason why a 50W panel may produce up to 3 times its rated output in a sunny day. Another drawback is the size of the panel, when you consider than in a 22' boat any space is much valuable. In a practical sense the only reason I would consider a solar panel is if I kept the boat in a mooring to avoid having to carry the battery back and forth.
The boat is kept at a dock during the season. There is no shore power at the dock. I am planning on keeping the solar panel in the boat while using it and then put out the solar panel while we are not at the boat.
 
Jan 11, 2014
7,847
Sabre 362 113 Fair Haven, NY
That is the reason why a 50W panel may produce up to 3 times its rated output in a sunny day.
Let me clarify this. Solar panels are rated in watts based on standard testing conditions, a certain amount of light at a certain angle to the sun, and at a certain temperature. An internet search will yield the specific numbers. When a panel is rated at say, 50 watts, it is rated under these optimal conditions. Those conditions are seldom met on a boat. The confusion may come from the difference between a watt and a watt hour.

Over the course of a day, panels on a boat are exposed to varying light conditions. Low angle early morning or late afternoon light produces some current, but no where near the rated capacity. Around midday, with the sun directly overhead it will produce power that is closer to its rated capacity because the sunlight is striking the panel at a more optimal angle, i.e, the sunlight is stronger.

In a solar charging system there are 2 key factors, how much power (current) can be produced at any given moment (the panel's rated output) and how much power can be generated over a period of time (watt-hours or amp-hours). A 50 watt solar panel under optimal conditions producing 50 watts for one hour will produce 50 watt hours of electricity. (roughly 4 amp hours at 12v). If it is exposed for 2 hours to these optimal conditions, it will produce 100 watt hours (roughly 8 amp hours at 12v).

In short, a panel can not exceed its rated capacity by any significant amount, but can produce less than its rated capacity due to a number of factors, heat, shading, cloud cover, angle to the sun etc.

When designing a solar system it is important to match power consumption and generation. If the consumption is 100 watt hours, at least 100 watt hours must be generated to recharge the battery. The power can be generated in any number of panel/power combinations, say 20 5 watt panels exposed for an hour, 5 20 watt panels, 2 50 watt panels or 1 100 watt panel. Because of the known inefficiencies in a charging system, it is helpful to have an estimate of the effectiveness of the panels. In a recent article in Professional Boatbuilding, Nigel Calder suggests that panels can be expected to produced three times their rated power over the course of a day. Thus, a 50 watt panel could be expected to produce 150 watt hours of energy. This is different from saying a 50 watt panel produces 150 watts.

The little solar "trickle chargers" are not very efficient. A 10 watt charger can only be expected to produce 30 watt hours a day, which is less than 3 amp-hours a day. Given the inefficiencies of battery charging, especially at higher state of charge, this is an insignificant about of power. Save your money, but a good charger and plug it in.
 

RussC

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Sep 11, 2015
1,530
Merit 22- Oregon lakes
On our Mac 25 we have a 30W solar panel which maintains a single 12v group 24 marine battery. besides a few led lights, we use a small Garmin chart plotter, cd player/radio, and usb charging ports etc. been using that for 4-5 years and it works quite well for multi day trips with no other charging available or needed.
On our Merit 22 we have a 20W system charging a small garden tractor battery and the loads include a couple led lights, a small Garmin, an electric keel winch (only used once per day) and usb charging ports. that system has also been quite satisfactory. both systems are mounted similar, to the stern rail where they are out of the way and maintenance free. This is the one on the Merit (which was under a blue tarp at the time of the pic):
IMG_0182.jpg

this isn't the exact unit, but very similar system to this one:
 

capta

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Jun 4, 2009
4,309
Pearson 530 Admiralty Bay, Bequia SVG
As mentioned above, you are going to get something considerably less than the rated watts over the day light hours, probably less than 30% even in the tropics, most of the time.
I think what many people tend to forget is their bilge pump in this scenario. Should your boat develop even a small leak, your bilge pump could be running hours up to full time over a 24 hour period. Since you'll get only a tiny amount of charging from the moon, you should consider this when choosing a battery, and the solar system to keep it charged.
Another thing I have noticed is that once folks have solar charging, they often want to increase their consumption (add a TV, etc), so it is not a bad idea to go larger now, for later needs.
You should also be aware that the hotter the panel, the less output it produces. Therefor, do not mount your panel(s) directly on the bimini or cabin, instead use a spacer so air can get to the back for cooling.
 
May 24, 2004
6,795
CC 30 South Florida
Let me clarify this. Solar panels are rated in watts based on standard testing conditions, a certain amount of light at a certain angle to the sun, and at a certain temperature. An internet search will yield the specific numbers. When a panel is rated at say, 50 watts, it is rated under these optimal conditions. Those conditions are seldom met on a boat.
Yes we are talking about oranges and apples. I'm referring to how a panel system is rated for marine use in practical terms. The panels output is measured over the average sunlight conditions as anticipated over a 5-7 days (sunny days, cloudy days, partly cloudy, rainy days, winter days, summer Days) period of average observed conditions for the area of use. While the maximum output rating of individual panels can be used for product comparisons the information is not as practical for a mariner as to what he needs and can anticipate in power production on the water. This rating is the starting point by which a system can be sized depending on power surveys with adjustments made for individual circumstances or needs.
 

AaronD

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Aug 10, 2014
537
Catalina 22 9874 Newberg, OR / Olympia, WA
@Erbardy : Some good advice here; I'll add my $.02:

1) Take the time to read all. of @Maine Sail's solar articles at Marine How To - DIY for Boaters - Marine How To (maybe start here).

2) @dlochner is totally correct about starting with your usage needs. If I understand correctly, you're normal use case is a few days of solar to recharge your batteries between weekend cruises. My guess is you'll find that a small panel (30-50w; 100w at the outside) will provide plenty of power for that usage (but don't take my guess - estimate your own usage before you spend the $$).

3) If you use flooded batteries, the Genasun GV-10 is worth a look - it's tiny, and the standby power draw is miniscule. But I think my top recommendation would be the Victron 15A. Similarly priced (at least from @Maine Sail) and more configurable (he'll pre-configure it for you for a reasonable fee, or you can buy the Bluetooth dongle and control it from a smartphone).

I use a Rogue 20A controller with a pair of 50w of semi-flexible panels; Rogue stopped making that unit, and if I was starting over, I'd almost certainly buy one of the Victron units.

As a very rough guess, you can figure on:
Controller: ~$150
Panel: ~$100 (cheap semi-flexible 50w)
Connectors and wire: ~$50 (MC-4, heat-shrink crimp, etc. See genuinedealz.com for most of those)
Through-deck: ~$25 (Scanstrut plastic - or $40-50 if you want the stainless ones)
Crimp tools: ~$75 (if you don't already have good ones for heat-shrink and MC-4 connectors; again, see marinehowto.com)

A sound investment, IMO.
 
Dec 28, 2015
1,357
Laser, Hunter H30 Cherubini Tacoma
I have two Renogy 125 watt panels a EPEVER 30 amp Triton controller, bluetooth module and a MT50 remote readout. The system pumps out 11 amps in late day, clear sky sun in April. I run a 4 battery bank and it keeps up with normal, conservative power use for 3-4 day trips with a refer system that uses 3-5 amps while running full on stereo with a single speaker, VHF and led cabin lights. I sail in the Puget Sound so there are normally a period of each day of motoring so charging via the alternator takes place also. I believe my system is balanced nicely.

I think a person can get overly detailed in the system (and need to) when using it like I do as a power source while in use. But as a battery charger between uses like you are describing, I think it a little over kill. I'd get a panel around 30 watts and a larger, high quality controller. I'd set the system up to be put away when not in use so you don't have to deal with mounting hardware. The reason for the larger controller is for expanding the system later in life. Up sizing the controller by a amp grouping isn't much extra.

A 30 watt panel is overkill also if the system is going to be sitting for a week between use but more is better but consider the concept if 30 watt panel won't fit anywhere.
 

Johnb

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Jan 22, 2008
1,295
Hunter 37-cutter Richmond CA

AaronD

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Aug 10, 2014
537
Catalina 22 9874 Newberg, OR / Olympia, WA
Everything I have got from Renogy has worked as advertised and seemed good quality (panels and controllers).

I have no opinion about sunpower.
:plus:
I haven't used enough alternatives to have real direct comparisons, but my overall impression is: Renogy is a cheap(ish) import brand - definitely not Solbian. But it seems to be a better import brand than most. Everything I've bought from them seemed pretty well made for the price point. And at Renogy prices, I can buy spares and replacements for almost anything (I would definitely think differently if I were doing offshore passages or world cruising outside the easy reach of Amazon).