How Many Watts Of Solar For Offshore Cruising?

[Burge]

Hi,

I am currently looking in to Solar panels with offshore sailing in mind and would like advice on how much Watt to go for.

The boat is a Farr 44 with engine driven refrigeration and most of the lighting is LED. There is a autopilot fitted but I am currently in the process of installing hydrovane so hopefully most of the time on passages I won't be running AP.

I have just fitted engine driven water maker so I will be running engine at least every other day to charge refrig, water maker and so will inadvertently also be charging batts. This has me thinking that I won't need to generate a huge amount of solar power to keep batts topped up.

I have three 130AH lead acid batts (390AH total.

I have been thinking along the line of 200-250 AH. I don't have solid dodger so I am limited to mounting Solar above DAvitts and on sides of push pit if required.

Is there any new solar technology worth considering?

Thanks in advance for your comments.

[sparrowhawk1]

I think you meant 200-250 watts. Over the years I've found a general rule to be to match the solar panels wattage with the batteries amp hours in other words 390 watts of solar panel. But more is better. if I were you I would fit as many solar panels on the davits as possible.

[StuM]

Originally Posted by sparrowhawk1

I think you meant 200-250 watts. Over the years I've found a general rule to be to match the solar panels wattage with the batteries amp hours in other words 390 watts of solar panel. But more is better. if I were you I would fit as many solar panels on the davits as possible.

Incidentally, 390 watts should hopefully generate in excess of 150Ah a day on average. Combined with the AH you will get from your alternator while running your engine for watermaking and refrigeration, I'd say that would be reasonable.

[Jim Cate]

No auto pilot loads? No refrigeration loads? No watermaker loads? Simple comms, instruments and lighting loads?

You will not need anything like 390 watts to stay even, even without the engine running every other day. When you throw that into the mix, your 200 +/- watts will be a generous plenty, unless you plan lots of travel in low sun angle short day areas.

To support this opinion, we have been full time cruising in the Australia/S. Pacific island area in this boat for 13 years now. Until a few months ago, we had 240 watts of very old-timey panels and a very simple PWM controller, driving 4xT105 golf cart batteries. We have 12 V refrigeration and a hungry autopilot, do a fair amount of Ham radio things and a lot of internet time on two laptops. This setup made us energy independent in the summer, and nearly so in the winter months. Adding in normal engine usage for movement in and out of anchorages, plus some general motoring in the winter kept us from needing additional engine hours for battery charging as a rule.

We recently added a 100 W semi flexible panel on the dodger with a cheapo MPPT controller. This location suffers from a lot of shading, but with some judicious boom shifting it has really made a difference. We now typically go into float mode by mid day. No winter experience yet, but the improvement in summer usage is noticeable.

Anyhow, don't get buffaloed into an awkwardly large and expensive solar array until it is proven necessary. I don't think it will be!

Jim

[mcarling]

I also don't think the OP needs a solar array, given what he has. In my opinion, a better investment would be replacing his lead-acid batteries with LiFePO4 batteries and a suitable voltage regulator for his alternator.

Alternatively, replace the lead-acid batteries with LiFePO4 batteries and get a small solar array, then toss the alternator.

[UNCIVILIZED]

Do you have a good amp hour meter, so as to keep judicious logs of how much juice you're using now? Plus what each system onboard, draws.
Such a thing would be pretty assistive, in more definitively answering said question.

[chuckr]

I will follow up from Jim Cate on the Caribbean and Med. We have 395watts with 3 solar panels and 6 t105 gold cart batteries. We run a 12v reefer, power hungry auto pilot, on occasion small water maker (pulls 8 amps for 3.5gal and hour), ham radio, and some internet and enough in the Caribbean (by Caribbean I am talking about both the eastern and western side) as the sun angle was good most of the year.
In the Med there is sufficient sun only part of the year and with a wind that is either too strong or not strong enough we do a lot of motoring so we charge our batteries with the engine a bit more.
I am going to add one more solar panel as we installed a 3024i controller and it has the ability to equalize the batteries if there is sufficient wattage coming in and right now I do not have it. We also would like a bit more charging from the panels here in the Med than we are getting.

We also do not have a hard dodger and built a frame over the dodger to mount them.

[MarkJ]

I don't think the OP needs any solar at all on this setup.

You are setting up what I consider to be a very bad solution to cruising long range and long term.

You absolutely must run your engine every second day at anchor or at sea where most boats now never have to run their engine except to get into the anchorage, and never at anchor. And it must be a great refigeration system to only need to be run ever second day.

You are talking about many engine hours per year just to run things that everyone else has configured to run off renewable energy.

If that one engine goes on the blink at sea or in port your whole situation deteriayes very quickly: at anchor to become uncomfortable, and at sea unsafe.

My thoughts are to be able to run all electrics off the solar panels. Watermaker usually an exception but often not needed much if restricting water usage when the engine plays up.



In general, as many solar panels as you can fit is excellent.

[Canibul]

we've got about 800 watts of solar now, looking seriously at replacing the glass and aluminum panels with 1200 watts in the next month. assuming we can sell a skiff to pay for it all.

I'll probably be adding more batteries, too. Thinking of more lead acid vs swapping to a different battery type.

On the solar, I want to be able to do what we want to do whether it's been cloudy for three days or not. We wnt to be able to run our inverter and tools and washing machine etc. without being reliant on fossil fuels for the day to day life.

[colemj]

Originally Posted by StuM

Incidentally, 390 watts should hopefully generate in excess of 150Ah a day on average. Combined with the AH you will get from your alternator while running your engine for watermaking and refrigeration, I'd say that would be reasonable.

I think that is optimistic. We have 700W and are struggling to make 150AH right now at 23°N.

To make your projection work, those panels would need to produce full rated current for 6.5hrs each day.

I would guess that amount of solar would produce 1/3-1/2 that daily output.

Mark

[sailorboy1]

Originally Posted by Burge

Hi,

I am currently looking in to Solar panels with offshore sailing in mind and would like advice on how much Watt to go for.

I think at most a 120W panel for you and that is mostly for using your autopilot and other underway loads and to fully get the batteries charged after running your engine for the other reasons. . I bet you run your engine at least daily for your setup and that will do bulk charging of your batteries, but you aren't going to want to have to run it a long time to fully charge them.

[captjcook]

The first thing is to figure your usage, add up all your daily loads then add a bit. This is what needs to be replaced, no real guessing involved. Do not count on more than 4-5 hours of solar when designing system, although it is frequently more. You might consider adding a 12v motor to run refer as backup/engine running alternative.

[a64pilot]

I find myself agreeing with Mark J, get rid of the enigne driven fridge, or if you stay with it, go with a big alt and maybe Life-Po as they can take a very high charge rate and done't mind PSOC, and skip Solar completely.
Your going to be running that engine daily, may as well ram amps into a bank that can accept a high charge rate and that PSOC won't kill.

Down side is if you lose engine, you lose everything, so have a Honda as a backup

[StuM]

Originally Posted by colemj

I think that is optimistic. We have 700W and are struggling to make 150AH right now at 23°N.

To make your projection work, those panels would need to produce full rated current for 6.5hrs each day.

I would guess that amount of solar would produce 1/3-1/2 that daily output.

Mark

390W @ 14.4 Volts (charging voltage) = 27 Amps peak power. That makes the 150 Ah about 5.5, not 6.5 hours.

700W and 150Ah - only about 3 hours peak power in the tropics?

I get a lot more than that out of my 800W.

Maybe I was a bit optimistic not knowing the OPs location but 5-6 hours is a reasonable rule of thumb unless you are primarily in overcast conditions.

Your 3 hours sounds very low for a tropical or sub tropical location. Are you using a MPPT controller?

[colemj]

Yes, mppt, but the panels are nominal 12V, so the mppt isn't doing much. Right now, the panel voltage is 15.4 and the battery voltage 13.5 - so a bit of help, but not much.

The problem is the panels are mounted flat, we have about 5-6hrs usable light (ie, above the panels), it is hot, and the sun this time of year never goes overhead, but travels lower to the horizon.

I still think 150AH out of 390W is unusual and optimistic. Using that assumption, we should be seeing 270AH, and that has never happened in the best of conditions in the tropics, although it would be possible in higher latitude summers.

Mark