How Many Watts Of Solar For Offshore Cruising?

[mcarling]

Originally Posted by StuM

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.

The extent to which solar panels are shaded by boom, sails, etc. varies a lot from one boat to another.

[reed1v]

We ran a 1200 watt capacity system on our ws43 for almost two decades. When your running radios, navigation equipment, water maker, a/c, and frig, you need that much. The system was designed to prevent overloads and that did happen on a daily basis not only in the tropics but in the polar regions where heat was essential. Btw, we ran the watermakers constantly so we did not have to clean the filters except occasionally. Also ran the navigation(including radar) and radios around the clock. If we had to do it all over again probably would have boosted the system to 2400 watt capacity.

We dragged a prop driven generator that kept the batteries charged while underway. More than enough power. At anchor, wind-solar-engine charging kept things going. Batteries never drawn down below the 75% level.

[Stu Jackson]

Mark and a64 and Jim C are right. He has literally NO electrical loads, the "living" stuff (fridge, watermaker) are engine driven. He doesn't need ANY solar. But re-read Mark's post: he has lousy systems for long term cruising if he doesn't want to use his engine every other day or even every day. He could build the biggest baddest solar array around and it wouldn't help him one bit.

[colemj]

Originally Posted by reed1v

Btw, we ran the watermakers constantly so we did not have to clean the filters except occasionally. .

I don't understand this. Filter clogging is directly proportional to the amount of water pulled through them. If you ran constantly, you would need to clean them MORE often, not less.

Mark

[Maka]

My sentiments exactly Mark

[sailorboy1]

Sometimes I think some of you use more power on your boat than I do in my HOUSE.

The OP has a couple of engine driven systems. I doubt he is interested in suggestion to get rid of them and replace them with DC systems and a bunch of solar $$$$$$$$. He just wanted suggestions based on what he has.

[Stu Jackson]

Originally Posted by sailorboy1

1. Sometimes I think some of you use more power on your boat than I do in my HOUSE.

2. The OP has a couple of engine driven systems. I doubt he is interested in suggestion to get rid of them and replace them with DC systems and a bunch of solar $$$$$$$$. He just wanted suggestions based on what he has.

1. Could be, but for some it IS their house, too.

2. Please see my #18 which referred to others' answers. Depends on what he wants to do and how he wants to run his boat. That said, experiences from the valuable members of this forum have indicated over the years that engine driven equipment, while it may be fine for some, has disadvantages as well, primarily lack of storage capacity of any kind for the energy being produced, other than the plates in the fridge. It's a use and management issue, that all.

[ramblinrod]

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.

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.

By removing refrigeration, watermaker, and autopilot from the picture, your daily consumption is likely around 50 A-hrs. (You should confirm this by performing a realistic energy audit.)

In this case, you battery capacity is fine and 200W of solar panel would be plenty.

As others have mentioned, current wisdom is to run more (like refrigeration and watermaker) off solar generated (and stored) electrical energy vs mechanical systems.

(Solar has no moving parts to wear out, is quiet, noise-free, is limited by available sun, but is not limited by availability of fuel.)

But it sounds like your investment is already made in the mechanical driven systems, so tis wise to base you solar on actual consumption expectations.

In this case, the goal of the solar should be to eliminate (to extent practical) need to run engine beyond powering mechanical devices. I would bet that in practice, you will run your engine powered refrigeration at least twice per day for 30 minutes each.

A missing piece of information is the size of your alternator. At 50% SOC, your battery bank (assuming standard FLA deep cycle) has an acceptance rate around 100 A (which will diminish as your SOC increases.

With a 390 A-hr bank, if you consume 50 A-hrs, and start with at a 50% SOC, a 40 A alternator would require about 200W of solar, a 60A alternator about 100W, and an 80A alternator would require no solar to keep up.

Notwithstanding, even if you system can currently generate all the electrical power needed, compared to your investment in mechanical systems, adding 200W of solar and a cheap PWM controller, would be low cost insurance of having ample energy on-board.

Full disclosure: I sell and install marine solar charging systems, and am offering this advice for free, with no intent to solicit business.

Ramblin Rod
Marine Service Provider
About Sheen Marine

[roland stockham]

l am with the 'this might be a problem' camp. Fridge running of the main engine is bad news. Running off the generator would be fine. Given that you have a pile invested in both the fridge and water-maker may make sense to look at a small gen-set they could be run off

[Stu Jackson]

Originally Posted by ramblinrod

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Notwithstanding, even if you system can currently generate all the electrical power needed, compared to your investment in mechanical systems, adding 200W of solar and a cheap PWM controller, would be low cost insurance of having ample energy on-board.

Good analysis. In addition, any alternator, almost regardless of how long it is run, and in this case it'd only be for short periods or when motoring to a destination, will never completely fill up the battery bank. Solar is superb for doing this. The result is your batteries will live longer.

[Burge]

I have been consideline adding a 12v Hp pump to the WM setup so could run off solar and have also considered adding a 12v refrigerator system as back up to engine driven system but where do you stop with the extra cost and weight of redundant systems.

[ramblinrod]

Originally Posted by Stu Jackson

Good analysis. In addition, any alternator, almost regardless of how long it is run, and in this case it'd only be for short periods or when motoring to a destination, will never completely fill up the battery bank. Solar is superb for doing this. The result is your batteries will live longer.

Correct.

Starting at 50% SOC with an 80 A alternator, running 1 hour per day would only add about 10 more A-hrs than the 50 (assumed) consumed.

At some point, of increased SOC, with diminishing acceptance rate, A-hrs consumed would equal A-hrs charged. This theoretical equilibrium point may end up being a constant (but of course they never are) daily charge cycle from say 65 to 80%.

Not a bad charging cycle target with an alternator. The occasional (biweekly or so) full charge (either from a full day of engine running, shore power charger, or solar charging system) will make batteries last longer.

If the financial budget would tolerate, I'd add the 200W solar just to enable a less deep and more full SOC on a daily basis, and eliminate the need for supplemental charging via other means, to top the batteries off now and again, and to allow for consuming more energy than budgeted on occasion.

Ramblin Rod

[poppyduc]

Originally Posted by 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

Just to add a few thoughts to the question. 12 volt system.
Have just installed 2 x 24 volt 250 watt panels and a Victron 100/50 mttp with Bluetooth Early days but I expect will work well. Showed first morning as sun just on panels 37 volts and 19 amps had to leave for work, so never saw full sun, but that appeared to be a good start.
A side note installed Victron on old 125 watt panels and it most definitely was a vast improvement on old simple regulator. More charge than ever seen before fm that setup.
Back for a week out in few days if anyone would like more info on how it produces let me know and will pass on data.
Fm past experience have noticed 24 volt panels produce even on cloudy days enough voltage to exceed 12 battery charge voltage.