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Ignorant solar panel and battery questions

Sep 13, 2021
61
Hunter 240 Lake Jacomo
Please forgive the ignorant questions. I searched in the forum but I might be more confused than ever now. :)

I have a Hunter 240. It has an electric start motor, cabin and running/nav lights, and a bilge pump. There are two 12volt power outlets that I have not used but might like to be able to use when overnighting to charge phones, etc. (if that's possible with our power setup). I think that's it for consumption.

There is a trickle charger hooked up to the battery.

We're on an inland lake, on a moor. I have access to shore power if I dock the boat and plug in the charger temporarily while we're tied up.

I have no idea how long to expect the battery to last under normal conditions before it would no longer start the motor or run the lights. It's a total guessing game. I just occasionally try to get to the dock and charge for a while.

I am thinking it might be smart to get a small solar panel that would keep it charged and also help out when we are overnighting on a weekend. I don't understand how large a panel I would need.

Any thoughts or advice would be appreciated! Feel free to point me to other resources. :)

Chris
 
Feb 26, 2004
21,950
Catalina 34 224 Maple Bay, BC, Canada
We all started somewhere. i suggest you buy Charlie Wing's excellent boating electrical systems book for starters. Here's more:

The All-Important Energy Budget:
Energy Budget

IMPORTANT BASICS What are amps & amp hours (thanks to StuM from CF.com)

Amps v Amp hours v Amps/Hr - Cruisers & Sailing Forums

Solar Systems: Selection, Installation & Controllers by Maine Sail SUPERB

Installing A Small Marine Solar System by Compass Marine How To

Do I Need a Controller for Solar?

Do I Need A Solar Charge Controller ??

Sizing wiring for solar Wire sizing calculator for Solar Panel Arrays

***************************

These links come from my Electrical Systems 101 Electrical Systems 101
 
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Jun 11, 2004
1,220
Oday 31 Redondo Beach
Stu Jackson's links will provide a wealth of reading and hopefully understanding.

Do you know what kind of battery you have and what condition it is in?
Good to start out with a good deep cycle battery in good gondition.

On a mooring, a small to medium solar panel would probably be a good idea to get you fully charged. It doesn't sound like you have much to power. It's the "etc" in your post that's the wild card. No refrigeration right? I know a lot of people might howl but you could probably get away with a 25 watt panel if you are just going one or two nights and start out with a fully charged battery. You don't need a fancy setup but you will most likely want a controller as discussed in one of Stu's links.

Get LED's for the lights. That will save a lot of amps.

If all else fails I assume you can start the motor with a pull rope right?
 
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Jan 11, 2014
7,826
Sabre 362 113 Fair Haven, NY
@Stu Jackson's advice is a great starting place.

One of the most important aspects of energy management is knowing what's coming in and what's going out, otherwise you are guessing.

The Victron Battery monitors are good and not all that expensive (depending of course on how you define expensive). They have some limitations, however they will give you a good idea about power consumption.

When it comes to looking at consumption, incandescent lights are a huge draw, swap out the bulbs for LEDs. The price of LEDs is now reasonable, buy a quality brand like Dr LED or from Marine Beam. The cheap ones sometimes cause more issues than they solve.

For your needs you will need a solar panel and controller with at least 50 to 100 watts. Don't waste money on low wattage "battery maintainers."

Read, learn, and ask questions. That's how all of us here learn.
 
Jan 7, 2011
2,911
Oday 322 East Chicago, IN
Is your motor an outboard? Does it have an alternator? How much do you motor when you go for a sail?

We also need to know more about the batteries…specifically type (lead-acid, AGM, ?) and size or Amp-hour capacity.

You seem to have modest power consumption needs, but to size a solar panel, we need more specifics…but it sounds like a modest solar setup would work for you.

Greg
 
Sep 13, 2021
61
Hunter 240 Lake Jacomo
We all started somewhere. i suggest you buy Charlie Wing's excellent boating electrical systems book for starters. Here's more:

The All-Important Energy Budget:
Energy Budget

IMPORTANT BASICS What are amps & amp hours (thanks to StuM from CF.com)

Amps v Amp hours v Amps/Hr - Cruisers & Sailing Forums

Solar Systems: Selection, Installation & Controllers by Maine Sail SUPERB

Installing A Small Marine Solar System by Compass Marine How To

Do I Need a Controller for Solar?

Do I Need A Solar Charge Controller ??

Sizing wiring for solar Wire sizing calculator for Solar Panel Arrays

***************************

These links come from my Electrical Systems 101 Electrical Systems 101
Thanks for all the information! I have some light reading to do! :)
 
Sep 13, 2021
61
Hunter 240 Lake Jacomo
Stu Jackson's links will provide a wealth of reading and hopefully understanding.

Do you know what kind of battery you have and what condition it is in?
Good to start out with a good deep cycle battery in good gondition.

On a mooring, a small to medium solar panel would probably be a good idea to get you fully charged. It doesn't sound like you have much to power. It's the "etc" in your post that's the wild card. No refrigeration right? I know a lot of people might howl but you could probably get away with a 25 watt panel if you are just going one or two nights and start out with a fully charged battery. You don't need a fancy setup but you will most likely want a controller as discussed in one of Stu's links.

Get LED's for the lights. That will save a lot of amps.

If all else fails I assume you can start the motor with a pull rope right?
I know it's a new this summer deep cycle battery, but I don't know the specs.

Nope, no refrigeration. We want to be able to run lights at night and potentially charge our mobile devices. Otherwise I'd say low power needs. LED replacement bulbs are on my list as well (assuming I can figure out how to access them :)).

You're right - I can use the pull rope.
 
Sep 13, 2021
61
Hunter 240 Lake Jacomo
@Stu Jackson's advice is a great starting place.

One of the most important aspects of energy management is knowing what's coming in and what's going out, otherwise you are guessing.

The Victron Battery monitors are good and not all that expensive (depending of course on how you define expensive). They have some limitations, however they will give you a good idea about power consumption.

When it comes to looking at consumption, incandescent lights are a huge draw, swap out the bulbs for LEDs. The price of LEDs is now reasonable, buy a quality brand like Dr LED or from Marine Beam. The cheap ones sometimes cause more issues than they solve.

For your needs you will need a solar panel and controller with at least 50 to 100 watts. Don't waste money on low wattage "battery maintainers."

Read, learn, and ask questions. That's how all of us here learn.
Yep, definitely planning an LED upgrade.

50 - 100 watts seems like a lot based on what I've read so far for my consumption needs. Why do you suggest that? Is it for a quicker recharge time?
 
Sep 13, 2021
61
Hunter 240 Lake Jacomo
Is your motor an outboard? Does it have an alternator? How much do you motor when you go for a sail?

We also need to know more about the batteries…specifically type (lead-acid, AGM, ?) and size or Amp-hour capacity.

You seem to have modest power consumption needs, but to size a solar panel, we need more specifics…but it sounds like a modest solar setup would work for you.

Greg
Yes, an outboard. No alternator. I don't know squat yet, so we're motoring quite a bit right now because we're learning. Ha ha

Unfortunately don't know my battery specs, but I'll look into that on our next visit.

Thanks!
 
Oct 24, 2010
2,399
Hunter 30 Everett, WA
A trickle charger is likely wrong. Some of them will certainly overcharge a battery if left connected. Conventional wisdom says a 3 stage charger is needed. Depending on your skill level if it's left plugged in, a float charger may be a better bet and they can be cheap. Measuring the voltage with a digital multimeter will tell you a great deal. For example, never let your battery drop below 12.11 volts while at rest. Never let resting voltage exceed upper limits I can't remember but I think that that would be around 13.5 volts. (You see without a proper 3 stage charger, you must take a more active part in battery management). It's gonna take some learning. If you don't leave the boat plugged in and just want to boost the battery, that's even another answer. As someone said a solar panel with a controller may be your best friend. Then you may be able to dispense with shore power altogether. On our 30 foot Hunter, I've used a portable 100-watt solar system and had good luck with it. And we do run the refrigerator in the daytime but click it off at night.

As I read dlochner's post below I should have elaborated. The idea for me of the portable 100-watt panel was to slow the bleed so we could spend more time on the hook without running that diesel-burning noisemaker. We don't often end up without shore power, but the solar really helps. Our house battery bank is rated at 234 amp hours, so it would take the solar a long time to actually bring it up from a 50% state of charge, but we haven't gotten that low while running the solar.
 
Last edited:
Jan 11, 2014
7,826
Sabre 362 113 Fair Haven, NY
Yep, definitely planning an LED upgrade.

50 - 100 watts seems like a lot based on what I've read so far for my consumption needs. Why do you suggest that? Is it for a quicker recharge time?
Without going in to too deep a dive here, there are 2 broad reasons involving how solar panel output is rated and how batteries accept a charge.

Battery charging is inherently inefficient. If you take 10 amphours of power out of a battery, you may need to put back 15 or more amphours. Thus, the more powerful the panels, the quicker the battery will recharge to a point. A 50 watt panel will typically provide 150 watt hours of power, which is about 12 or 13 amphours in a day. Assuming you have 70 amphour battery (a group 24) and you use the 35 amphours (half the capacity) it will take at least 3 days for the panel to recharge the battery assuming no inefficiency. If you have a 25 watt panel, it will take at least 6 days, again assuming no inefficiency which there will be. Forget about 10 watt panels.

Which brings us to solar panel ratings. Panels are rated under standard conditions which are optimized to provide the most power. Your panels will seldom if ever see these conditions. I have 2 high quality 150 watt solar panels, most days the best the panels will provide at peak is about 100 to 120 watts each and then that is only for a couple of hours a day. Most of the day the power output is much less. On a good day with lots of sunshine, my panels will produce about 4 times their rated power, 500 to 600 watt-hours each ( ~1,100 watt-hours). Lower cost and lower quality panels will only produce about 3 times their rated power. And then there are days where my panels produce next to nothing due to a heavy overcast.

This is the reader's digest version, as you learn more about batteries, charging, and solar the issues will become clearer, but first they will be muddy and opaque. Hang in there and beware there is a lot of mythology out there about electrical systems.
 
Jan 19, 2010
9,999
Hunter 26 Charleston
Unless you have an inverter on your boat, you cannot use the standard outlets to charge your phone unless you are connected to shore power. It is reather easy to install a "cigarette lighter" charger that would be 12V.
 
Sep 13, 2021
61
Hunter 240 Lake Jacomo
Unless you have an inverter on your boat, you cannot use the standard outlets to charge your phone unless you are connected to shore power. It is reather easy to install a "cigarette lighter" charger that would be 12V.
It's the "cigarette lighter" style outlets we have now. We don't have real "shore power" with 110-style outlets and a port on the outside of the boat. I assumed I could plug phone chargers into them since I can do that in a car. Is that not true?
 
Jan 4, 2013
252
Catalina 270 Rochester, NY
In 2019 I lost shore power due to flooding on Lake Ontario. I purchased a 30 watt panel (Suner Power) from Amazon that came with a controller. I mounted the controller to the battery, run the cable over the hatch boards, and leave the panel on the cockpit seats. Works great.
 

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Sep 13, 2021
61
Hunter 240 Lake Jacomo
In 2019 I lost shore power due to flooding on Lake Ontario. I purchased a 30 watt panel (Suner Power) from Amazon that came with a controller. I mounted the controller to the battery, run the cable over the hatch boards, and leave the panel on the cockpit seats. Works great.
Thanks - this is exactly the kind of simple solution I'm hoping for.
 
Mar 2, 2019
210
Oday 25 Milwaukee
We are also on a mooring . It seems most folks responding to your post missed that. Suggesting 50 or 100 watt solar panels for a 24 foot boat is realistically not going to work . Those are fine if you have a 30 foot or bigger boat . We have a 20 watt panel ,roughly 18"x 27" mounted above and behind the stern railing .
That panel feeds battery "A" . Battery "B" gets recharged from the outboard . Most small outboards that have an charging circuit put out a very small amount of amperage .Even then it's at full throttle . Eventually you are going to want to use a chartplotter ,depth sounder ,fishfinder ,music and possibly an autopilot. Most of these can be done with notebooks ,smart tablets or phones . you might want to think about the battery packs that folks use to power up phones and blue tooth speakers . They are easy to charge at home and take along to the boat . We also use them when we travel by other means
 
Sep 13, 2021
61
Hunter 240 Lake Jacomo
We are also on a mooring . It seems most folks responding to your post missed that. Suggesting 50 or 100 watt solar panels for a 24 foot boat is realistically not going to work . Those are fine if you have a 30 foot or bigger boat . We have a 20 watt panel ,roughly 18"x 27" mounted above and behind the stern railing .
That panel feeds battery "A" . Battery "B" gets recharged from the outboard . Most small outboards that have an charging circuit put out a very small amount of amperage .Even then it's at full throttle . Eventually you are going to want to use a chartplotter ,depth sounder ,fishfinder ,music and possibly an autopilot. Most of these can be done with notebooks ,smart tablets or phones . you might want to think about the battery packs that folks use to power up phones and blue tooth speakers . They are easy to charge at home and take along to the boat . We also use them when we travel by other means
Thanks - yeah, we already use the portable batteries for our phones. They are handy. I'm mostly just trying to make sure our battery stays topped off and healthy and that we don't worry about completely draining it if we want to use cabin lights for a while at night. Right now we're paranoid to use lights because we don't know how long the battery charge lasts and don't know when we'll be able to plug in to shore again.
 
Jan 11, 2014
7,826
Sabre 362 113 Fair Haven, NY
The recommendation for a 50 to 100 watt panel has nothing to do with the size of the boat, it is about what it takes to charge a battery and to prevent sulfating and the premature death of the the battery.

The math is pretty simple.

Watts = Voltage * Amperage, so a 20 Watt panel produces 20/12 = 1.75 amps

Nigel Calder suggests that most solar panels can at best about 3 times their nominal output in a day. With a 20 watt panel, that is 60 watt-hours or 5 amphours. This is consistent with my experience on my boat.

Charging a battery is not 100% efficient, especially as the battery approaches a full charge. The inefficiency means not all of the current that can be produced can actually charge the battery, lots of the energy being produced becomes heat.

Charging a dead iPad will require about 5Ah (see link below) which is about equal to what a 20 watt panel produces on a good day.

Small boats, such as Hunter 240s and 270s have Group 24 batteries which have a total capacity of about 70Ah. Following the standard advice of not discharging the battery more than 50%, yields 35Ah available. Recharging with a 20 watt panel would take at least 7 perfect days to provide those 35Ahs, assuming100% efficiency.

A 50 watt panel will produce about 150 watt-hours (12 Ahs) a day. Again, assuming no inefficiencies, the panel will recharge the battery from 50% in about 3 days of good sunshine.

Why worry about how long it takes to recharge? The longer a battery spends in a partial state of charge (PSOC) the shorter the life of the battery because the battery will sulfate. This is a big issue with AGM batteries as well as Flooded Lead Acid batteries.

Look at it another way. While sailing and using an iPad a 20 watt panel will barely provide enough energy on a good day to power it while a 50 watt panel will.

Some things to remember, panels seldom if ever produce their rated output, count on 50% to 60% as typical. Battery charging is inefficient, it takes more energy to recharge a battery than was taken from the battery.

This is why panels in the 50+ watt range are recommended. The smaller ones are just not up to the task.


 
Mar 2, 2019
210
Oday 25 Milwaukee
I stand by my assertion about the 20 watt . I understand that you need to resupply the amperage used . However , you folks with 30 foot and bigger boats seem to have forgotten a basic premise. There is no convenient place to mount 100 watt panels on a 24 foot boat !
Renogy lists a 100 watt panel having the dimensions of 42"x20" x1.5" . That's roughly 4 feet by 2 feet . Are you mounting this on the hatch where it is constantly being moved back and forth? In front of the mast where it is likely to be stepped on when ever someone goes forward to anchor or bring down the jib or attach a dockline ?
I'm speaking from practical experience . Yes in a perfect world , throw a 100 watt solar panel on top of a rigid bimini . Out of sight out of mind .