Solar Boat Questions

Re: Solar Boat Questions

Welcome to the forum Solar Boat guy.

I have moved your questions to its own thread. It usually is less confusing if your questions are the focus of your thread.

Boat grounding is a difficult question to answer easily.

There are the basic safety grounds. There are problems with electrolysis eating away prop and motor bearings, ship board power/dock power, and lightning/radio grounding.

So--Rather than jumping in on a detailed and totally irrelevant (to you) discussion... Some quick questions.

Is there a gasoline motor or generator on the boat? Is this purely electric propulsion from battery bank? Will this be at a dock with an AC battery charger? Andy lights/AC power/etc. on board?

Where will the boat be operated (amount of sun per day). Roof rack mounted panels (probably flat, no tilt).

There is an issue with needing both 24 volts and 12 volts (running/cockpit lighting/radios)... In general, it is a very bad idea to have a 24 volt battery bank and draw 12 volts from the middle of the bank--It forces the batteries "out of balance". We can work around it a bit to get 12/24 volts from a 24 volt bank, but it usually costs significant amounts of money (24 to 12 volt converter)--So there may be a choice to go 24 volt only for lighting or even going with a small/efficient AC inverter and go with 120 VAC lighting/power.

Grounding such a system (small pontoon boat) is not an "operational issue". A solar power system can be "floating" to all metal on the boat and work very efficiently and safely. Grounding is mainly done for safety reasons (electric shock, short circuit protection, lightning protection, etc.). Are any of those issues for you? Any local Coast Guard inspections? etc.?

-Bill

Re: Solar Boat Questions

SBG, not sure why you had problems with the forum software... Make sure you have cookies enabled for this site, and if you have any sort of "java scripting" disabled, make sure java script is turned on.

If you are on a smart phone--I use Android and find the browsers to be a bit "sensitive" on this forum when posting.

In the upper left of the editing window is a button with an A/A symbol. If you click once on that button, it toggles to "dumb edit" mode which is easier to use on my phone.

Regarding design of your system... Pretty much anything you want to do, can usually be done pretty safety.

However, solar power systems tend to produce less power than most people think, and most people use more power than the realize. So, knowing you loads (amp*hours or kWH or watt*hours per day) usage lets us understand the amount of power you need, then we can work backwards into sizing the battery bank and solar array.

However, we can work the other way too--You have XYZ AH of AB voltage battery bank. Or you have room for ZZZ watts of solar panel, etc...

And if you have local power at the dock for recharging, then you may not be limited by the size of solar array (i.e., solar will help, but charging at the dock will supply the rest of the needed power).

So, looking at the motor website:

Attachment not found.

A "400 series motor" (nice match at 48 volts, the other voltage are "not standard" for solar RE equipment). There is a 10:1 scaling between low speed and high speed current (amps). That is not a small spread in power usage (38 hours to 2 hours on the same "example" battery bank--Look to be 6 volt ~220 AH golf cart batteries). And that is too "battery dead"--Your batteries will not last long if taken to dead often.

So, rather than me randomly picking some numbers... You give me what your desires are (battery bank voltage/Amp*Hours, solar array sizing, xy amps at ab hours for motor, etc.).

And then I can answer your question "exactly without going out in the weeds with possibly irrelavent guesses/answers on my part.

-Bill

Re: Solar Boat Questions

Hi Joe, hope you are finding it easier to post now.

Regarding Rates of Charge--5% is the minimum that we usually recommend for recharging a lightly used solar power system (not too deep of loads, used on weekends, etc.).

For systems that are heavily used (daily), use "tall cased batteries", and/or heavy traction batteries (forklift), 10-13% rate of charge is usually a better choice (batteries use more current to stir the electrolyte, heavy plate batteries tend to have higher self discharge as they age and need more solar array power to break even with loads).

Generally, "golf cart batteries" are going to cost less--And they will not last as long as "higher end" batteries (say 3-5 years vs 5-8+ years for "better" deep cycle batteries which probably cost 2x as much).

I will also "argue" that "slow boats" are dramatically affected by adverse currents and winds--So, I would be very careful about long distance trips unless you have that reliable gasoline/diesel back up propulsion system (and understand the local currents/winds/forecasts, etc.).

So--Lets start with some known performance requirements. 32 amps @ 6 hours... Normally, we would suggest a maximum of 50% of battery discharge for long cycle life (traction batteries could go as low as 20% state of charge--but they will be more expensive, heavier, and take a lot of solar array to recharge). Note that the 50% cycling gives you both room for the battery to "age" and a margin of safety for your boat.

For the moment, lets say you will use good quality golf cart class batteries. You want:

• 32 amps * 6 hours * 1/0.50 maximum discharge = 384 AH @ 48 volts

A Trojan T-105 6 Volt, 225 AH Deep Cycle Battery will have ~200 AH capacity at a C/12 discharge rate (6 hour rate to 50% discharge = 12 hour discharge rate).

So, for a 48 volt battery bank @~400 AH 48 volt battery bank would require 16 of these batteries (two strings of 8 in parallel ~$151 per battery).

The size of solar array to recharge this battery bank would range 5% to 13% (or as high as 25% or so--but that is another conversation):

• 2*225 AH * 59 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 1,724 Watt array minimum
• 2*225 AH * 59 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 3,448 Watt array nominal
• 2*225 AH * 59 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 4,482 Watt array "cost effective" maximum

And for a solar array based on the amount of power you use. Lets guess that you get 5+ hours of sun per day (sunny Mexico) from a flat mounted array (need to confirm):
32 amps * 6 hours * 59 volts charging * 1/0.77 panel+controller derating * 1/5 hours of noon-time sun per day = 2,942 Watt array minimum

So--Just at a first look, I would guess that "ideally" a 2,942 to 3,448 watt array would be a good range (especially if you use "tall case" batteries and/or "forklift" type batteries).

If you do not go out to maximum range every day, and you use "short case" batteries... Plus you may have shore power to recharge/backup AC generator (when needed), you could go down to ~1,724 Watt array.

There is somewhat of a "conflict" between running loads during the day and recharging during the day... Basically, if you have a 5% minimum array (~22 amp charging) and a 32 amp load--Obviously, the battery bank will not recharge when under way (although, the solar array will add significantly to your range on a sunny day).

So--If you have 1-2 (up to 4) days of "rest" between long distance sailings, you will probably be fine.

There are other ways to "cycle" a battery bank (i.e., charge to 80% and discharge to 50% every day, and recharge to >90% every 5-10 days--actually a very efficient method of cycling good quality deep cycle batteries)--But we don't really need to discuss that at the moment.

I would highly suggest you get a Battery Monitor (Victron is another good unit) to allow you to better monitor the how your battery banks are being used/recharged (sort of like putting a "fuel gauge" on your battery bank).

The fact that this battery bank is on a boat may give you some help with 5% charging on a "tall case battery". Motion of the boat should help keep electrolyte better mixed.

Anyway--That is a first cut at the basic numbers. Not arguing that my way is the only way--But it is a starting point. Batteries are heavy, expensive, and store a surprisingly small amount of power. Solar power systems make sense when you use the power 9+ months a year--And less sense if it is seasonal usage (batteries are expensive and age even when stored)...

Just to give you an idea, a ~1,000 lbs for the above battery bank:

• 440 AH * 48 volts * 0.50 discharge = 10,556 Watt*Hours = 10.6 kWH Hours

That is about as much "electrical energy" as 2-3 gallons of gasoline through a Honda eu2000i 1,600 watt genset.

-Bill