Question about solar panels and batteries.

kappykaplan · Nov 13, 2024

What is the size (amp hours) for the house bank? How many solar panels and what is their wattage?

DArcy · Nov 13, 2024

That's a very open question with a lot of variables. The fist thing, maybe the most important for your specific case, what is the size and condition of your battery bank? List the loads and duty cycles to determine your consumption in Amp-hours then compare this to your battery capacity. In addition to the navigation equipment you mentioned, you likely have a refrigerator, autopilot, cabin lights, navigation lights.

Many boats still have the 1/Both/2 switch when allows use of either battery or both. These setups generally have two batteries of the same size and they are used for both house and engine starting. Other setups have a dedicated engine battery with a separate house bank. The house bank would generally have higher capacity in this case. If you have a separate engine battery that is not used for house loads you have low risk running out of juice since you can always start the engine to charge the batteries.

I have 250 Watts of solar and it keeps up, without autopilot use, such that I don't need shore power. I still have incandescent cabin lights, but navigation lights are LED. My refrigerator is not very well sealed so it runs about 50% duty cycle in the warm days of summer.

If you don't have a battery monitor then you are guessing at the state of charge. A volt meter helps here, I installed one so I can always see battery voltage. If you keep the battery voltage above 12.2V you are ok. Keep an eye on it and start the engine to charge if it drops to 12.2V. It's a good idea to keep an eye on battery state of charge so you don't run them down too low and damage them.

With a large house battery bank you could probably make the entire trip without charging. With a smaller bank you would likely need to run the engine for and hour or two along the way. Old batteries, or newer ones that have been abused, won't be able to hold a charge as well.

JoeWhite · Nov 13, 2024

Before you start your trip, at the dock with no shore power, turn on all the instruments that you will be using while sailing for 12 hours using the house battery with starting battery disconnected. Then measure the house battery voltage. If it is much less than 12.2 vdc, then you need new batteries. But it is likely that the solar panels will supply all the current that is needed for the instrument so the battery will not be discharging most of the day.

dlochner · Nov 13, 2024

As others have said, too many variables to give any kind of a reasonable answer and you don't want to spend a bunch of money on the electrical system without a lot of forethought and planning, that stuff ain't cheap.

Once you find the boat you want to buy, ask about the batteries, how old they are, how long since they have been on a charger, what kind of use they have had, what size are they. This will help ascertain their condition and whether they are up for the trip. If you have any concerns about the batteries and their condition, just replace them. Don't go to West Marine, you'll pay a premium. Try Costco or any national Auto Parts store, think cheap and disposable. It will cost you a couple of hundred dollars for new batteries, but that will buy you some time to research and decide what you will do to the electrical system to meet your needs.

Next, buy towing insurance from TowBoatUS or SeaTow. If the batteries fail, they'll come get you. The USCG won't unless someone's life is at stake (the prior owner and broker don't count if they mislead you and you want to end their existence).

And this winter begin your education on all things marine electrical. For an organized course, check out BoatHowTo.com. This is a site developed by Nigel Calder a guru for all boat systems especially electrical. I have been to his seminars and he can explain complex ideas in a way we mere mortals can understand. It is a pay course, but well worth the money spent.

A second choice is MarineHowTo.com This is Rod Collins' site. He is especially good at dealing with specific issues and questions. Get to know his site and what's on it. Rod's site is free, however, if you can help him out by donation or using his affiliate links that would be beneficial.

Finally, don't hesitate to return and ask questions. Just be prepared for a deluge of answers to sort through.

Good luck with your search! :beer:

https://boathowto.com/

Marine How To - DIY for Boaters - Marine How To

For DIY boaters in an attempt to try and keep the sport as affordable & safe as possible. How To articles for sailboats and powerboats.

marinehowto.com

Johann · Nov 13, 2024

Great advice here. Another good resource from Nigel Calder is his Mechanical and Electrical manual. The website seems to focus on electrical… This covers quite a bit for a first time sailboat owner.

Amazon.com

mermike · Nov 13, 2024

Charlie Wing's book is also excellent.

jssailem · Nov 14, 2024

Welcome Max (mad or sane) to the SBO forums. Some might say you have lost your sanity buying a boat. For sure you will lighten your wallet. The experiences you will have will bring much joy.

With that out of the way, let us explore your questions. I take it you are interested in a Catalina 36. That is a lot of boat for a beginner, and you'll face a steep earning curve.

"I understand that most sailboats came with two batteries, one for engine-starting only (inboard engine) and another for powering the instruments (radar, AIS, some interior lighting, etc)."

More accurately, boats can come with two "Battery Banks." It is not an automatic condition. Each back can be comprised of one or more batteries. The type of Battery chemistry (Lead Acid, AGM, Lithium, etc) determines the amount of usable battery energy you have stored in each battery. It also affects the systems you need on the boat to recharge the batteries.

"To keep the batteries charged while sailing (not using the shore power), the solar panels will keep the batteries charged, is that correct?"
- Not really. Depends on how the panels are attached on the boat, the type of panel installed. It is not really necessary to maintain battery charging while day sailing. You can design electrical storage that will provide adequate power until you can recharge.
"If the engine is running, it will charge the batteries but I don't plan to keep the engine running all the time while sailing."
- This is rational. I am not sailing while the motor is running. Sometimes, I will motor with a sail up to assist in boat balance in a complex sea state. While sailing, I may not need all of the electrical systems active. I control the amount of stored energy I remove from my batteries.
"My #1 concern: After I purchase a sailboat, I'll need to move it from a marina to my "home port" marina which is about 65-70 nautical miles. That means I'll have to sail for about 10-12 hours. I want to keep the instruments running all day (GPS, AIS, etc) while sailing. I'm concerned that I might run out of battery juice."
- The first action plan regarding the electrical system (this is not the first level of concern for me on a new boat, but it is high on my priority list before I leave the dock) is to identify the capacity of the batteries. It is important to know how much stored energy there is, what type of batteries I have, and how much capacity (amp hours) they can provide. Your books will help you understand this issue. With most systems, you can sail the 10-12 hours if leaving with fully charged batteries. Your plan to sail 65-70 nm may take longer if the wind (like most of the time) is not steady. Plan your first trip with stop points halfway at a marina. This allows you to recharge overnight and will help you acclimate to the boating experience. 10 hours on a sailboat in the Pacific Ocean is a long time for a new boater. It will wear you out.
"Do you think the solar panels will keep the battery charged (maybe 80% or higher)?"
- Without any details as to the solar panel cell types, how they are attached to the boat, and the weather conditions of your trip, it is impossible to give you a definitive answer. Likely, No is my first thought.
"What's the minimum wattage (solar panels) to keep the battery fully charged?"
- This is another good question that requires more information before a calculated answer can be provided. You want enough solar but not too much. You'll need to know the battery chemistry and the battery charging parameters. It would also be nice to identify how much time you need for the batteries to reach "Full Charge" before you decide on the panel wattage to source.

This will be an exciting new adventure for you and your crews.
Let us know the boat you finally select.

BarryL · Nov 14, 2024

Hi,

Lost of good information above.

I will make it simple for you.

The battery stores power. The alternator makes power. The instruments, lights, radios, etc. all use power. Some / most boats have two separate battery banks, so if one becomes too discharged to start the engine, the other battery can be used to start the engine (and then all battery banks get charged).

When you are sailing (no engine) you are using power from the battery. After you deplete the battery you need to run the engine to replace what was used. When you are motoring you are producing power, which will be used by the instruments, etc and the excess will be stored in the battery (until the battery if full).

That's it in a nutshell.

TYPICALLY, during a DELIVERY, there will be periods of time when there is not enough wind to sail, or the wind is from the wrong direction. During those times you will run the engine so you can make it to your destination in a timely manner. GENERALLY, you will run the engine often enough to not have to worry about the batteries. If you get lucky and have enough wind and from a good direction, you may need to run the engine for an hour or two to recharge.

More information
If you plan on being aboard your boat for extended periods of time, then solar makes good sense because you will be charging the batteries during the day and discharging them at night by running the lights, refrigeration, etc. If your boat will be in a marina with shore power, then solar isn't really required.
My boat stays on a mooring during the season. I have a 100W solar panel that I put in the cockpit when I'm not aboard. That keeps the batteries charged so when I get aboard I have full power. My boat is sort of complicated with refrigeration, powered winches and windlass, bow thruster, lots of electronics, and things like that. I also mostly daysail - on the boat for a few hours, mostly sailing, little motoring. The solar panel means I never have to worry about the batteries not being charged.

Welcome to SBO and Good luck

Barry

Dave · Nov 14, 2024

BarryL said:
Welcome to Sailnet and Good luck

Barry

Ahem..... Trying to get on Santa's Naughty List?

BarryL · Nov 15, 2024

OOPS!!!

Dave said:
Ahem..... Trying to get on Santa's Naughty List?

Kings Gambit · Nov 15, 2024

Good Morning,

You are wishing to sail 70 n.mi. or so from location x to Shoreline Marina in Long Beach in the coming Spring and you wish to know if your house battery bank will last out running navigation instruments? Assuming no fridge, no autopilot running, and no running lights?

A difficult question to answer here not knowing the condition of your batteries. IMO, start off with a new, dual-purpose starter/deep-cycle flooded cell, lead-acid battery. You likely will not sail that distance off southern Califorina in 10 to 12 hr unless you are sailing a reach all day in 13 kt or more of true wind, which is unusual. Your VMG would have to stay at 7 kt SOG or greater to make 70 n.mi. in 10 hr. (Can your boat even make 7 kt of STW?) If you wish to make the trip during daylight period of 12 h you’ll probably be motoring half or more of the time. Your battery demand will therefore be more like five or six hours, maybe less. A new 100 ah dual-purpose battery will give at least 50 ah to work with without stressing the battery, etc. An 80-watt solar panel might actually deliver 4 or 5 ah total between sunrise and set in April.

So, add up the demand of your instruments in amp hours/hour x 6, and you will have your answer, or nearly so.

Happy sails to you.

LloydB · Nov 15, 2024

Welcome to SBO you picked a good time to ask these questions. Considering your main concern as stated in getting the sailboat you have your eye on to your home port, you may well have to motor the entire 60 miles or better at 5 miles an hour so plan an early morning start because there is a possibility you will have used all the electricity available to you in the first half of the trip.( the shortest distance between two points is upwind) Your analogy of the car electrical system compared to a sailboat may work somewhat however a better comparison might be between everyday commuter car and a camping trailer or an executive motor home, it depends. As far as solar is concerned you need to understand that a small 200 Watt solar panel probably needs 250 watts of sunshine before night and no matter how sophisticated your charging system is if you've got a 50 Watt battery you've only got 50 watts of use.(kinda) You will be glad you found this site because the people that are here and the answers you get are friendly and knowledgeable.

Tin Kicker · Nov 16, 2024

I like simple. The link shows percentage state of charge for AGM battery voltage levels. I have a small version of this above my battery selector knob. Take a copy with you so you can occasionally monitor as you go.

Complete Guide: All about AGM Battery Voltage

Complete guide for AGM batteries and learn all the applications for amg batteries.

www.renogy.com

Keep the power coming from the house side and leave the start motor isolated. If the state of charge gets too low simply start the motor and let it run in neutral if under sail.

Calif. Ted · Nov 16, 2024

It takes twice, sometimes 3 times as long to SAIL up coast as down. I don't use solar panels, maybe you won't need them unless you spend more than a few days at anchor or moored.

Scott T-Bird · Nov 17, 2024

madmax said:
I hope I'll get at least 250 watts of solar panels for my boat.

Why do you want solar panels? Will you be in a marina with shore power or will you be on a mooring? If you will have shore power, find out if the prospective boat has a good battery charger system. If not, plan on an upgrade. You will have little need for solar if you rely primarily on shore power. If you are on a mooring, then you may want to upgrade with solar charging. Previous owner of my boat was on a mooring and had solar panels. Consequently, he had an inadequate battery charger since he had no opportunity to use it. I upgraded the charger and ditched the solar panels when I moved the boat to a marina. The panels were very old and I didn't need the weight on top of the bimini.

Of course if you are planning on multiple day anchorages, you will want solar. I can't imagine why you wouldn't be able to sail and/or motor sail your planned trip without the need for solar panels if your new boat is suitably provided with adequate battery capacity for a 34' boat (if that is the approximate size you are seeking}. The boat should have at least 200 amp hours (more likely 400 amp hours) house bank and probably a small auxiliary battery for starting or back up if it is a typical set up for a Catalina 34.

You will have to fill in the details of what is on board for anybody to give you a suitable answer. And, of coarse, the seller may be leaving you with an entirely unsuitable bank of batteries if he is negligent about condition and unwilling to spend money prior to selling the boat. Buyer Beware! It's something to pay attention to when you are shopping!

Kings Gambit · Nov 18, 2024

madmax said:
Because I'll be on a mooring at Santa Catalina Island (approximately 25 NM from Long beach), I'll likely purchase a boat without solar panels and can get a whole system of solar panels, new batteries, etc. Yes, I am planning to spend several days mooring (and might go around the island, it'll be fun).

Your original question appears to have expanded. You now seem to also be asking about keeping your batteries up for a few to several days, at least, while on a mooring in a place with no shore power options. Different question; different answer.

Yes, solar panels would be one component of battery power management at anchor. Refrigeration, or lack of it, is an influential variable in that equation, as would be AC power needs. It’s possible to supply more wattage to a battery bank in a day than it can absorb, depending on its condition (age), etc. Most deep-cycle batteries charge slowly. There’s a balance factor there.

Question about solar panels and batteries.

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SBO Weather and Forecasting Forum Jim & John

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