A question probably asked, so pardon me if I repeat it.

[Jammer]

Originally Posted by wallythacker

My boat should handle 4 solar panels on the arch over the transom, add another 6 flexible panels on my bimini, then add another another 4 on the cabin roof for a total of 14 panels without looking like a utility pole. If each panel is 150 watts that is 2100 watts of energy, then add another 800 from the two wind generators for a total power plant production of 2900 watts.

::shrug:: you will have problems with shading on the bimini and cabin roof. You will have problems with windage with a transom arch that large. Think hard about how the panels are attached to the arch and how the arch is attached to the boat. It will have to withstand a gale, unless you're planning on disassembling it and stowing it below in threatening weather.


Two large wind turbines will tend to shade some of the panels and pose their own fairly serious mounting difficulties due to the forces and vibration involved. On an average basis, you will not get as much energy harvest per day from 400 watts of rated capacity of wind as you will from 400 watts of rated capacity of solar.

I do realize asking for 16.5kbtu of AC is HUGE. The advice given to run just one unit, the 5kbtu one and duct the cool around where needed is good advice. It has me thinking of how to install flappers on my air system so I have complete control of where the cold air flows. I don't think anyone has gone that far yet, perhaps I'm wrong and someone has a way to micro manage their AC.

You will find that you cannot save energy by using a smaller AC or by using ducting. If you use too small an AC then the space will not get cooled. If you try to cool half the space you will still have substantially more than half the cooling load unless you have a dividing wall between the cooled and uncooled space that is perfectly insulated and has no air leaks.

I'm primarily motivated to see if everything the boat has can be utilized, more or less on demand, when away from the dock......without using the generator. So truly being off the grid when off the grid.

The answer is that it can't without tradeoffs that most people would find unworthwhile. It seems to me that you do not like this answer.


Do you actually have the funding to pay for the kinds of systems you're talking about, or is this all just, how shall we say, a hypothetical example?

[wallythacker]

Originally Posted by Jammer

Do you actually have the funding to pay for the kinds of systems you're talking about, or is this all just, how shall we say, a hypothetical example?

The money is there, it's just a matter of deciding if the cost & effort is worth the end result.

Not wishing to drag this out forever there's a 2009 thread here that deals with this issue; http://www.cruisersforum.com/forums/...g-28239-4.html

and it mentions a 3500btu cruiseair that sips 13a@12v or 130ah to replenish after a 10 hour run.

This site computes needed btu's to reach a desired temp. Very handy;https://www.calculator.net/btu-calcu...=heat&x=78&y=8

The boat in question is a 45 Columbia, big flat roof, room for an arch that will hold 5 panels, or maybe just a large bimini with 6 flexible panels, or a mix and match. Should I choose to go with an arch and bimini panels I doubt I'll mount panels around the rail.

I'm confident that power production and power plant management will get better, fairly quickly, just look at the sail system that is a large solar panel.

[john61ct]

Note that in hot weather a 3500 BTU unit will only cool a very well sealed / insulated space.

Basing plans on predicted future vaporware is not sensible.

[valhalla360]

I think the amps for the 3500btu air/con are a bit off: See the link below which shows 30amp @ 12v and that doesn't include the seawater pump which typically run 1-2amps at 120v (figure 10-20amps at 12v for similar power).

So now that 13amps became 40-50amps...so 400-500amp-hr to run 10hr. (Really more when you factor in system losses)

And keep in mind such a small unit will be limited to a very small cabin to achieve any noticeable cooling and where a larger unit by cycle on and off to keep cool (drawing nothing when off), that little unit will likely run 100% of the time in even modest heat.

https://www.dometic.com/en-us/us/pro...ddy-ii-_-21015

Yes, you can generate and store 400-500amp-hr but it's going to be a very expensive option relative to the minimal cooling it can provide.

[john61ct]

Yes, those running small aircon from solar that I know are doing so direct from 1200-1500W panels in sunny conditions.

They do not bother trying to do so from battery storage.

And more panels are required to also charge batteries for the other House loads.

For aircon when it isn't bright sunny, or for more than the small 8x8 insulated space, the genny is needed.

[Nicholson58]

Originally Posted by wallythacker

I think the answer is already known but here's my question regardless.

Is it possible to install enough solar and wind using today's tech to run a watermaker part time, say, 10% of the day? along with running a 16.5k btu AC unit 50% of the day, run the fridge and normal devices and maintain a neutral balance on the battery bank?

Maybe I should be asking how many watts (is that the proper measure?) does my power plant need to produce to achieve what I'm requesting?

Yes on the watermaker, not so likely on the AC. We run a 24 VDC Spectra 200T. On a good solar day IN the Caribbean, we run it from 9 AM to about 3 PM on 660 watts of panels with MPPT controller. Water maker runs every five days to satisfy our needs. We also run DC refrigerator and freezer. Total of all three is 12 amps while the panels produce 19 to 22 amps.

[Jammer]

Originally Posted by wallythacker

and it mentions a 3500btu cruiseair that sips 13a@12v or 130ah to replenish after a 10 hour run.

That would be this unit, which actually draws 29 amps, per the manufacturer.

This site computes needed btu's to reach a desired temp. Very handy;https://www.calculator.net/btu-calcu...=heat&x=78&y=8

That is a residential calculator, and a dumbed-down one at that.

You will not be able to achieve sufficient cooling of the cabin of your 45' boat with 3500 BTU/h. The calculator is giving you the wrong answer for three reasons:

1) It is a heating calculator, not a cooling one, and therefore calculates only the sensible cooling load, not the latent cooling load. In humid conditions, as would be the case on a boat, the latent cooling load is large, possibly larger than the sensible load.

2) The insulation on any boat is not as good as the typical insulation on a house.

3) Air infiltration on a boat poses a disproportionate share of the cooling load, because it is not feasible to close the companionway quickly and completely on most boats after passing through it.


The full residential calculation is available as something called "Manual J."


You're embarking on a $10,000 project. It won't work. You'll have to triple the cooling capacity (at least), and then you won't have enough solar capacity to run the cooling, and then you'll end up doing what everyone else does and either leave the air conditioning off or run the engine (or generator).

[3Days_at_a_time]

Originally Posted by LoudMusic

I'm sitting on 900Ah of LFP and 700w of solar. I think I'd double my LFP and triple my solar to be able to run one 10,000 BTU aircon through the night.

Now to find that sunken treasure to make all my dreams come true ...

We run a 7000BTU unit of a 420ah battery bank and 450W of solar from about 8pm to 7am every day on our trips. Works fine for us. we occasionally have to skip a night here and there depending on cloud cover.

[CapnCrunch]

Originally Posted by wallythacker

Is it possible to install enough solar and wind using today's tech to run a watermaker part time, say, 10% of the day? along with running a 16.5k btu AC unit 50% of the day, run the fridge and normal devices and maintain a neutral balance on the battery bank?

I havent read all of the responses so, hopefully, someone else hasnt posted this. I dont know what brand your a/c is, but my Webasto 16k btu draws a whopping 54 amps when the compressor kicks in. Could this amount of surge overload your inverter?

My bank is "rated" for 960Ah and runs thru a 2500w inverter, but I only run the a/c on shore power or my generator. Speaking of gennys; we didnt want a big, loud unit, so we have a Honda 2000! The a/c surged would overload this genny in a heartbeat, so we bought an EasyStart unit (@$300) which, through some kind of magic, runs the a/c nicely. The only downside of this setup is that, if you're in a mooring field, your neighbors may object to the noise because, while the genny is pretty quiet in "Eco" mode, it runs in normal mode when powering the a/c and is noticeably louder.

[3Days_at_a_time]

Originally Posted by CapnCrunch

I havent read all of the responses so, hopefully, someone else hasnt posted this. I dont know what brand your a/c is, but my Webasto 16k btu draws a whopping 54 amps when the compressor kicks in. Could this amount of surge overload your inverter?

Our inverter is rated for inrush currents much greater than most generators, it is rated for a 3X surge for 20 seconds. that 9000W... or 78A. so while the easystart would definitely make it easier on the inverter, it can definitely handle it.

[a64pilot]

Originally Posted by 3Days_at_a_time

We run a 7000BTU unit of a 420ah battery bank and 450W of solar from about 8pm to 7am every day on our trips. Works fine for us. we occasionally have to skip a night here and there depending on cloud cover.

What do you do doing the day?
My 5,000 BTU AC which is not very efficient draws 6 amps with water pump at 120 VDC, or with inverter inefficiencies about 65 amps of so off of battery.
With my other house loads, fridge etc. I have an 80 amp load on my bank.
If you assume a 50% duty cycle and 12 hours then the AC alone draws 6x 65= 390 AH, which takes my 660 AH house bank below the recommended 50% discharge, and my 1,000 W Solar bank can’t replenish that in one day, cause we all know you get on average only about 1/3 rated power in Watts for AH, so I get 333 AH, plus of course nothing is 100% efficient so I need to generate at least another 30 AH to recharge.

Oh, and then what about house loads?

You need depending on conditions a 1000 AH bank if lead acid and probably 2KW of Solar to run a small AC all night, assuming a 50% duty cycle. Ideally you want an LFP bank

My assumption is your duty cycle is much less than 50% and that is why you can do it, much less. But how are you recharging during the day? I assume motoring to another destination?

See I have a small 5,000 BTU AC with it’s own water pump etc that cools only our Stateroom and head. I can run it, just barely off of our 165 amp alternator, it’s nice if your motoring on one of those still, windless July or Aug days in Fl.
Just barely cause I don’t get 165 amps, alternator would burn up, and I have house loads too of course, and a bilge blower etc when the engine is running, and all of those have to be powered too.

[a64pilot]

Originally Posted by CapnCrunch

I havent read all of the responses so, hopefully, someone else hasnt posted this. I dont know what brand your a/c is, but my Webasto 16k btu draws a whopping 54 amps when the compressor kicks in. Could this amount of surge overload your inverter?

My Magnum MS 2812 inverter which is 2800 continuous, but will surge much higher depending on time interval, like 4,000 or higher will not start our Webasto 16K unit, it will however start the little 5 or 6K whichever it is Webasto easily.
Which easy start did you get? I put a Supco easy start cap on our 16K AC and I’d didn’t seem to help much if at all, but it wasn’t $300 either.

[3Days_at_a_time]

Our house loads, lights, fridge, electronics come from the house bank which is recharged by the motor, I should have mentioned that. We are a motor boat so we do run the big motor often. The solar is connected to it's own battery bank, and only powers the inverter. It can be connected to the house bank to keep those batteries charged as well, but I only do that when we aren't using the boat since we move often enough to keep that bank charged with the alternator when we are on board. The AC takes 900W while it's running, we don't use it during the day very often because we are usually not sitting in the cabin very often. It runs at most a 50 percent duty cycle once the boat is cooled down.

[Happ]

Simple answer is yes depending on the type of boat, mono vs multihull, the power drain on the batteries, and the type of batteries. To start you need to find what your usage is going to. Then figure type, size and number of batteries required. Now move on to how many solar panels will be required based on the amount of sun you will get and the charge the solar panels will provide. Go to www.batterystuff.com. Great tutorials. I'm not affiliated but have used them and they are great. By the way 16,000 BTU is the size recommended for 38' monohulls.

Once you have figured all this out you might want to look at many options that are available at lesser cost. For instance look at Rain Man water maker. It is a portable unit powered by a small Honda motor. As someone else mentioned there are small portable AC units good for a cabin and run off a USB port. Look at Amazon some are less than $50. No affiliation. Minimize your usage and everything gets much simpler.

It all comes down to how big is your need, how big is your boat, and how much you want to spend.

[john61ct]

Yes a full-fledged motor cruiser changes the picture completely.