Solar - Trying to keep this simple and not to technical.

[JScottHuston]

We have a cutter sloop with:

- ONE (1) 4D 12v for the engine battery

&

- SIX (6) T-105 6v batteries wired in as twelve volt banks with a total of 600 amp hours (if my math is correct).

I charge them using shore power, the alternator on a running engine or a Honda 2000 Generator thru a Xantrex Freedom 3000 inverter/charger. I have all of this on an A/B switch to select house, engine or all (in and out) as well as Xantrex Link Line battery monitor.

I'd like to lay a portable panel on the deck while out on a mooring over weekends. Mostly to offset the refrig, radio & amp, lights, and various lite duty use for phone charging, etc. (We're not heavy on burning power during the day other than refrig and radio.) I'm hoping to minimize running the Honda 2000 at night, leaving a fully charged bank to run the TV, refrig and lights at night.

Is there a brand, size & output I should focus on that would work well during the day and could be stowed when not in use? And I guess I would install that into the A/B switch?

Any insight is appreciated.

[Scot McPherson]

The bigger the better, get as big a panel as you can fit on your deck and on top of any houses if you have them. defender.com has lots of choices.

[thinwater]

And you posted this on a forum, thinking it could stay simple....

Portable panels. Actually, there is no such thing. The roll-up panels produce trivial power for the space they take, so IMO we can discard those out of hand. The semi-flexible panels use the same silicon cells as rigid panels, only without and aluminum frame and glass top for protection. The cells accumulate micro fractures very easily. Even slight repeated flexing reduced power output quickly, and the installation manuals always caution you to avoid handling. They are meant to be bent to a curve ONE TIME and then left alone. The marketing people whistle a different tune, but the engineering side corrects them. Really, you need to find a place for fixed panels, preferably rigid, though semi-flexible on a smooth, firm surface can work. However, they will not last as long as rigid panels, perhaps 1/3.

Output. With the loads you describe and a 600 AH bank, you are kidding yourself with anything less than 200 watts. That will produce only 60 AH in typical sunny weather with no shading. Any shading AT ALL and it can be a fraction of that. This is why you see big solar arrays. Assuming you can use 1/3 of the bank overnight (if you have a fridge you ARE a heavy user), 600 watts are required. But only you know how much power you use. BTW, I doubt your neighbors like the Honda 2000 at night.

Wire. Even portable panels require fat wire to be effective. The 200 watts I mentioned would require perhaps 8 AMG, depending on the run. That is 2x the largest extension cord you will find, just as a reference.

You need an MPPT charge controller unless you will be DEDICATED to watching the batteries. I would not risk it.

Generally these are wired straight to the bus, with fusing.

Unfortunately, usable solar is not that simple. But it's not that bad either. Commit.

[JScottHuston]

Huge thanks for the input. I was hoping to work with my CFO's (MRS.) budget but my effort may be better spent on waiting.

[txg]

If you've got 600Ah, are on shore power normally and only need to power light loads for weekend trips, there is absolutely no need for solar.

Your bank should easily last for at least three days without recharging, if this is not the case either your batteries are getting too old or you have something (perhaps unknown) onboard that uses a lot of power.

[DeepFrz]

Some people successfully mount their solar panels to the life lines or rails. That keeps them away from the shading and can be switched from side to side depending on the direction of the sun. Heavy weather comes up and they can be removed and stored below.

[john61ct]

Originally Posted by thinwater

Wire. Even portable panels require fat wire to be effective. The 200 watts I mentioned would require perhaps 8 AMG, depending on the run. That is 2x the largest extension cord you will find, just as a reference.

You need an MPPT charge controller

An MPPT with high volts capacity will allow putting panels in series, which will reduce the gauge needed.

But downside is, this will increase the hit from partial shading.

[thinwater]

Originally Posted by txg

If you've got 600Ah, are on shore power normally and only need to power light loads for weekend trips, there is absolutely no need for solar.

Your bank should easily last for at least three days without recharging, if this is not the case either your batteries are getting too old or you have something (perhaps unknown) on board that uses a lot of power.

Obviously the OP needs a power budget. Add up the amps x hours of everything and check that against the amount the batteries are actually down. I would be shocked if it was lets than 100 AH/day. This can be reduced by not running the fridge and use LED and florescent lighting. With 600 AH in batteries you have 600 x (85%-50%) = 210 AH usable capacity, unless you want to beat the batteries down, so about 2 nights. You will get some engine charging if you motor a lot, but that does not help if you stay in one place. There is the generator, but most of us hate those. Solar is pretty weak when there are clouds. Usually it takes some of everything.

Read-up, get some economical panels and a controller, and the system should pay for itself within ~ 10-20 marina nights. A bargain.

[newhaul]

If you have a pushpit it is not to difficult to mount a couple 100 watt panels on it and running them thru a pwm controller you can get away with spending under 300 usd if you do theinstall yourself . I have done several for.cuztomers. pm for specifics.

[john61ct]

Originally Posted by thinwater

With 600 AH in batteries you have 600 x (85%-50%) = 210 AH usable capacity, unless you want to beat the batteries down

No reason to avoid the top 15%, unless you mean can't fully recharge, which IS "beating them down" as much or more than going below 50%.

So 300 AH available for use , at least in the first part of their lifetime.

[Uncle Bob]

Originally Posted by newhaul

If you have a pushpit it is not to difficult to mount a couple 100 watt panels on it and running them thru a pwm controller you can get away with spending under 300 usd if you do theinstall yourself . I have done several for.cuztomers. pm for specifics.

+1 Doesn't have to be worlds best practice, I have 190 watts to golf cart batteries via morningstar pwm controller, similar loads with no problem.

[newhaul]

Originally Posted by thinwater

Obviously the OP needs a power budget. Add up the amps x hours of everything and check that against the amount the batteries are actually down. I would be shocked if it was lets than 100 AH/day. This can be reduced by not running the fridge and use LED and florescent lighting. With 600 AH in batteries you have 600 x (85%-50%) = 210 AH usable capacity, unless you want to beat the batteries down, so about 2 nights. You will get some engine charging if you motor a lot, but that does not help if you stay in one place. There is the generator, but most of us hate those. Solar is pretty weak when there are clouds. Usually it takes some of everything.

Read-up, get some economical panels and a controller, and the system should pay for itself within ~ 10-20 marina nights. A bargain.

The op has 300ah nom to work with at the start of each weekend. Or did you miss the part about being on shorepower except on weekends when on the hook

[newhaul]

Originally Posted by Uncle Bob

+1 Doesn't have to be worlds best practice, I have 190 watts to golf cart batteries via morningstar pwm controller, similar loads with no problem.

I have a 100 watt panel on my pushpit thru a 10dollar pwm controller
Pictures in my profile album

[Pete7]

JS, can't recommend a make but style yes. How about a suitcase solar panel which folds up when not in use. We have a 60w panel which because we can angle it directly at the sun several times a day is very efficient compared to fixed panels which won't always be aligned efficiently. Check how big they are before buying, clearly bigger is better for charging but can you store it somewhere safe and move it about without scratching the woodwork.

Something like this perhaps:

100W Suitcase Folding Solar Panel12V Portable Kit DIY Camping Adventure Car New | eBay

[roland stockham]

Generally portable panels are to keep batteries maintained when the boat is not in use and all systems are off. For a 6ooa/h bank you would be looking for 6-12 a/h day ie 170-140 watt hours. Depending on location and season something around 50w would do this and be easy to put on deck and stow.
If you want it to keep services running such as a fridge the panel size will be to big for this and you need a permanently installed system with an mppt controller and need to do all the calculations to get it right or you will be either disappointed or spend more money than you need! From your list my guess would be around 200w of panels but a lot depends on the efficiency of the fridge. If they battery monitor has a means of measuring a/h consumed measure how much you use for a w/e to give you a good ball park number to start from.