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Old 14-04-2021, 11:52   #1
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Generator or No generator, that is the question

Hi Fellow Sailors,

We are putting together a energy system for our 40 ft Catamaran.
Please can we get your suggestions on the below:-

We will be powering, lights, laptop, navigation, fans and other day-to-day household needs.
We will on occasion utilise a washing machine, aircon and small low amp dishwasher.

Could we do this without a generator and by just having the right lithuim battery, inverter and solar panels? And if so How much AH lithium batteries and how much solar Watts would we need?

Thanks.
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Old 14-04-2021, 12:13   #2
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Re: Generator or No generator, that is the question

With a ton of solar and good battery bank you could run everything on your list except aircon.


But separate genset might not be needed in any case. Put big enough second alternators on the propulsion engines and you could use that, provided you deal with overloading (no full alternator power whilst motoring at medium RPM).
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Old 14-04-2021, 12:22   #3
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Re: Generator or No generator, that is the question

I agree with everything Dockhead said except that you can run aircon from a big enough inverter and battery bank. It just needs to be REAL BIG. We successfully run one 12K BTU unit from a 2800W inverter and 1200Ah of 12v battery bank and 2100W of solar. To be practical you need more. Or a DC aircon unit.

If you want to live on your boat like you live in your house, you're looking at 2000Ah of usable battery capacity, 6000w to 10000w of inverter power, and 5000w of solar. AND house bank alternators on your engines is a good idea too because sometimes the sun doesn't shine for five days in a row and then you're pooched.

Hey Dockhead - do you have a recommendation for those inverters?
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Old 14-04-2021, 12:33   #4
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Re: Generator or No generator, that is the question

Quote:
Originally Posted by MarkHopk View Post
Hi Fellow Sailors,

We are putting together a energy system for our 40 ft Catamaran.
Please can we get your suggestions on the below:-

We will be powering, lights, laptop, navigation, fans and other day-to-day household needs.
We will on occasion utilise a washing machine, aircon and small low amp dishwasher.

Could we do this without a generator and by just having the right lithuim battery, inverter and solar panels? And if so How much AH lithium batteries and how much solar Watts would we need?

Thanks.
A lot depends on how much AC. 8 hours of AC is a huge amount of energy likely more than everything else you will do on your boat combined.

You have two different limits.

Inverter. Your inverter must be properly sized to handle the peak load of your AC loads combined. A 14,000 BTU AC is going to be about 10A @120V or 1,200W. If you have two then that is 2,400W right there.

Energy Capacity: Running a 14,000 BTU AC for 8 hours is going to use 5,000 to 10,000 Wh or 420 to 840 Ah @ 12V. Two of them well is going to be double that.

Realistically you are going to want to have a generator. With a collosal amount of solar and an incredibly large battery bank you could get away with not having one and just running your main engine an hour or two each morning but realistically if you have an AC and certainly if you have two you will want a generator.
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Old 14-04-2021, 12:55   #5
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Re: Generator or No generator, that is the question

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Could we do this without a generator and by just having the right lithuim battery, inverter and solar panels?
I feel the answer is NO! You need I feel you need at least a Honda generator, 300-600W solar (depending on your generator use), and 20 AH of useable battery capacity (you decide want that means to you and what type of battery).

This is based on my real use experience on a 43' sailboat my wife and I cruise full time.
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Old 14-04-2021, 13:31   #6
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Re: Generator or No generator, that is the question

Actually the answer is yes! A lot of cat owners have converted to large lithium banks and big solar arrays. I mean A LOT.

Having said that, I wouldn't. IMO, I'd go with a small, as small as they come, generator. Probably a Fischer Panda 4kw. I'd have that automatically come on when the bank gets discharged by a certain percentage. That way, instead of investing in massive solar panels, battery banks, and absolutely needing sun every day, you can cut back on half of it and still be very, very energy efficient. And it's cheaper after looking at the cost of the panels, structure, and batteries.

I really dislike the looks of boats that add so much solar they look like wings of aircraft. I really can't imagine sailing with those wings in the open ocean in 50 knots. My guess is some of them blow off but you don't hear about it because the owners are embarrassed. Could be wrong.
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Old 14-04-2021, 13:38   #7
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Re: Generator or No generator, that is the question

Quote:
Originally Posted by Dockhead View Post
With a ton of solar and good battery bank you could run everything on your list except aircon.


But separate genset might not be needed in any case. Put big enough second alternators on the propulsion engines and you could use that, provided you deal with overloading (no full alternator power whilst motoring at medium RPM).
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Old 14-04-2021, 13:53   #8
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Re: Generator or No generator, that is the question

In my case, I find that use of a generator is typically to run 110v items.....power tools...etc..it can off course, run the a/c's and charge the batteries, but these are rarely in use once the dock is left behind..
A small inverter can take care of the odd 110v appliance....TV, etc...

For the rest, solar panels keeps up with everything else..

It's nice to have, but necessary....hmmmm??

An installation does not come cheap....there is the genset....sound insulation....intake thru' hulls, water strainer, wet exhaust system, new fuel lines, fuel filters, hoses, plus installation time, etc, etc... a wild guess would be $15K by the time you are done.....maybe more, considering the haulout...$20K ???

Finally, and no small matter is the weight, and where this weight will be located on the boat...a location where it is easily serviceable as well...???
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Old 14-04-2021, 15:00   #9
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Re: Generator or No generator, that is the question

Quote:
Originally Posted by LoudMusic View Post
.

If you want to live on your boat like you live in your house, you're looking at 2000Ah of usable battery capacity, 6000w to 10000w of inverter power, and 5000w of solar.
We live on our boat just like we did at the dirt house
Same washing machine, same 42 inch tv and 32 upstairs
multiple PC and monitors
But with more refrigeration than we had at the dirt house, all on 24/7


We have 880Ah of battery @ 24v, 5000w of inverter and 2500w of solar.

Been doing just fine for near 5 years now.

Do need Genset for cloudy days and lower angles in winter.
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Old 14-04-2021, 15:12   #10
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Re: Generator or No generator, that is the question

GENERATOR
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Old 14-04-2021, 15:29   #11
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Re: Generator or No generator, that is the question

I have lived on both sides of this debate.


Previous boat -- solar, lead-acid batteries. Current boat -- heavy duty 6.5kW Kohler low speed generator and no solar.


Previous boat we were happy as clams. No aircon off solar, but you dont' really need aircon at anchor, even in Florida. Current boat is set up to sail upwind long distances, which the previous boat was not capable of. Therefore, on a monohull, no solar. Generator is great.


Pick your poison. I love my generator, but wouldn't want the third diesel engine on a cat. Not necessary.
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Old 14-04-2021, 15:38   #12
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Re: Generator or No generator, that is the question

At anchor I rarely have needed an air conditioner except in shallow water in the keys at night and it is very difficult to put enough solar on a 40 ft boat to run an air conditioner on the hook. Since you want to run a washer you can do it with about 300 ah usable if you are not running a dry cycle. I have 640 watts of solar and 210 ah usable and can do that without the dryer though the washer still runs the batteries down a bit. The dryer takes about 100 amps out of the batteries for as long as it's running. Usually about an hour. We have a 5kw genset and can run the water maker, washer, heat water and one ac unit if we start the AC and water maker first as they take a lot of startup power. Every once in a while I have been stuck at anchor in the rain for 3 ot 4 days. Without ventilation because all the hatches are closed and no solar power the genset has come in handy to charge batteries and run an AC unit just to dry things out. I'm not sure you need a $10K genset to do that but a 2.2kw Honda or equivalent might really come in handy now and then. Under normal circumstances we do one genset run a week while on the hook and do all our washing and water making. My old diesel genset gave up after 16 years and we did replace it, but that was a choice because our cat doesn't have any practical place to put more solar without building an arch and that would cost almost as much as the genset (with the additional solar).
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Old 14-04-2021, 16:34   #13
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Re: Generator or No generator, that is the question

we are full time live aboard on a 40' cat. all the creature comforts...3 fridge / freezers etc, but no a/c.

only 650w of solar + 400w wind + 660ah of battery, but that is enough for us during summer or if in tropics (plan to upgrade this as soon as we win the lottery)

however during winter or in latitudes where the sun is low or when it's cloudy, we fall back on our trusty 6kva diesel generator. as a safety net, would not be without it - you'd need an unreasonably large area of solar to deal with 3-4 days of rain & solid overcast

i know folk who have 1kw of solar, not overly large energy demand - and still need their gennie from time to time

finally, don't forget to add a wind generator to the mix. they don't produce much, but can go all night and do make a diff to the overall state of charge.

cheers,
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Old 15-04-2021, 02:04   #14
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Re: Generator or No generator, that is the question

Designing an effective boat system that works well with or without a marine diesel generator is quite different. This is why when questions like this crop up on the forum those with a generator cannot imagine running the boat comfortably without a generator and those without a generator cannot imagine needing one. In truth both systems can be made to work well.

Personally, I prefer the reliability, simplicity and lack of maintenance associated with designing the boat to run off predominantly solar charging and without a generator, but this is not the correct answer for everyone.

If you want to run air conditioning at anchor then a generator based system is generally better. It is possible to run some air conditioning from just solar, but only on largish cats, and the system complexity rises, defeating many (but not all) of the advantages typically found on a solar boat.

Other than air conditioning, solar equiped boats can offer all the comforts, including the greatest luxury of all, which is the reliability and time to enjoy the cruising lifestyle.
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Old 15-04-2021, 02:16   #15
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Re: Generator or No generator, that is the question

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. . . Other than air conditioning, solar equiped boats can offer all the comforts, including the greatest luxury of all, which is the reliability and time to enjoy the cruising lifestyle.
Amen. Our last boat was solar only and what a luxury. It never occurred to us that we might need a generator. We had air conditioning and were cruising in the tropics, but we only really needed the aircon at the dock where shore power was available.

HOWEVER, the big problem with a large solar installation on a monohull is windage. The previous boat sailed like a pig upwind so I didn't worry about it, but this one will go upwind so I wouldn't spoil that with a giant speed brake.

The OP has a cat so won't have this problem. If I had a cat, I would go solar and forget about a generator.


For occasional stretches of cloudy weather, a school bus alternator on one (or better both) main engines is perfecftly adequate backup power source. This has an enormous advantage of simplicity, ruggedness, cheapness, cmopared to an AC generator. You'll save a lot of weight too.


We didn't even have that on our previous boat and we were fine.
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