Air Conditioning via Solar Panels

[Hugh Howey]

Yup. It's possible. It's not cheap, but it changes life aboard.

A few years ago, I commissioned and launched a 50' catamaran with 1.75kw of solar on the roof and 900Ah of 24V lithium batteries. The batteries and inverter proved beefy enough to run two AC units for a few hours at a time, or a single AC unit for 6 or so hours before the generator needed to kick on. I also elected to install a DC generator instead of an AC generator. Everything on the boat is designed to run off the battery bank. The solar array, engine alternators, and DC genset are there just to dump amps into the batteries.

It was an amazing setup. Crossing the Atlantic -- 6,000 miles from South Africa to the Caribbean -- the genset kicked on twice. And we only motored for half a day across the doldrums. The joy of lots of solar and big batteries allowed for life aboard to resemble apartment living (big screen TV, fridges, freezers, hot water, even AC for brief spells).

This was a far cry from my first 5 years living on a boat, where I didn't have a shower or toilet. Nothing wrong with either kind of sailing if you ask me; this thread is about what's possible, not what's necessary.

When I got to Australia for my first refit in three years, I decided to add more solar and two more batteries to my current system. Part of the reason for adding the solar was to extend the bimini out to either side for more shade and rain protection in the cockpit / helm. I was also hoping (dreaming, really) of having a system where AC can be run during sunny days without draining the batteries.

This isn't to sit in the AC on beautiful days; it's to control humidity, mildew, and the wear-and-tear of moisture and a marine environment on personal electronics, clothing, bedding, etc. I live full-time on my boat, and I spend a lot of time in the tropics at anchor in very remote places. Energy independence without sacrificing comfort was the pie-in-the-sky dream. This week, I saw that it is possible.

With 4 more high efficiency 350W LG solar panels, total wattage is now just north of 3kw. Two more Mastervolt batteries gives the 24V bank a total of 1,260Ah.

On a very sunny and abnormally humid day in Australia, we launched the boat and ran the AC for the first time. With the compressor running, the solar was still putting over 20 amps into the batteries! Cooling and dehumidifying the boat while topping up the batteries at the same time!

What I love about this setup is you only need the power when you have the power. When the sun is blasting, you get free air conditioning. And by free, I mean the panels and batteries cost an arm and a leg. But once you have them, life at anchor can be whatever kind of life you prefer.

Battery and solar prices keep coming down while efficiencies go up. I hope what I'm seeing on my boat becomes the norm one day. Fewer generators being installed, more electric engines, more happy cruisers who are out enjoying the nice weather instead of doing the bedding again or treating the forepeak for mildew.

[Thalas]

Thanks for the great writeup. It's nice to hear real world numbers and the results from them. 3kw of solar is no joke and now I need to go research DC generators as I've never even heard of them before.

Thank you for pointing out the ancillary benefits to something like A/C. I feel like so often there is binary judgement from posters on "luxury" at sea and free dehumidification is nothing to sneeze at as a fantastic side benefit. Obviously this means you can run dive compressors, water maker, etc with much less fuel and hours on the genny.

I think more boat builders are going to switch to 24v as the default wiring setup as the market demands more power at sea.

[Hugh Howey]

Thanks, Thales!

A DC genset means all my systems run off the batteries, either directly as 24V systems, or off an inverter for 110V items. Nothing runs off the genset. It simply pumps juice into the batteries via a regulator.

My water maker is 24V DC.

My genset is wired to automatically turn on when my bank hits 35%. It shuts off at 80%. All I have to do is check the oil now and then.

The genset used to come on once a week or so, depending. I doubt it'll ever run now. I'll watch how the system works and will likely pull the genset and sell it. (I'll run it an hour a week to keep the oil moving)

Hugh

[Bean Counter]

What inverter do you use and what cost?

[Hugh Howey]

Originally Posted by Bean Counter

What inverter do you use and what cost?

The entire system is MasterVolt. I don't know what the inverter cost, as it was priced into the build of the boat and the total electrical system. Not sure the model number either. I'll check on that (unmaking the day bed in the saloon to look under the cushions is no joy).

[john61ct]

I'd be very interested in details on your DC generator. Is it a unit packaged by a single vendor, or a stock engine custom-coupled to a high-performance alternator?

[Hugh Howey]

Originally Posted by john61ct

I'd be very interested in details on your DC generator. Is it a unit packaged by a single vendor, or a stock engine custom-coupled to a high-performance alternator?

It's a Fisher Panda unit. The alternator is built into the unit. It comes in a sound suppressing fully enclosed case. The self start module interfaces with the Mastervolt panel.

You probably already know, but will state for anyone not familiar: The advantages of a DC genset include lower noise and greater efficiency. They don't have to run at 50/60 hertz multiples, so they can throttle to the charging demand. If an AC genset is mostly being used to charge batteries, it doesn't make a lot of sense. You're making AC to power a battery charger to get DC.

[Thalas]

So, with an inverter as robust as this with a full 20 seconds of 18000w surge capability to handle compressor startup...

https://tinyurl.com/y8h8jg6h
6000 Watt Low Frequency Inverter 110/220Vac Split Phase, 20 seconds of 18000 Watt Surge

what is the advantage of using an AC generator vs a DC generator? Is it more efficient?

[a64pilot]

AC power generation is more efficient, way more available, and requires wiring of much, much smaller size to carry the same power, and chargers are very, very efficient too now.
There are few actual DC generators, most actually make AC power and rectifying it to pulsating DC within the generator, so most DC generators, really are not.

If your use of a generator is to charge a large Lithium bank, then your running at close to max output anyway, so the theoretical advantage of reducing RPM of a DC genset evaporates.

[john61ct]

I assume the voltage output is well regulated and user-adjustable?

Prefer not to add the cost of multiple quality chargers to total say, 240A

Fischer BTW, being German

[Oceanride007]

Have a friend now sailing south that advocates his DC generator, have messaged him, will post the info when I get it.


Meanwhile have a new best friend who sails a Mono (looks like a 43'Bene) and claims to be running a window AC unit on solar, will visit him in a few days. He has a Honda as well. Looks like has 3 rows of flexible panels, bent on to a rigid bimini assume 1200Watts. But he is away.
New best friend cose he will sort my freezer issues.





Opinion here.

DC generator doesn't have sound deadoning, maybe half price to similar powered AC, don't need big charger.



Either way you still need a big inverter.

[Oceanride007]

Here is a DC generator. This is Aussie based.


https://www.macfarlanegenerators.com...arger-12V-120A


Not so cheap anymore.

[a64pilot]

Issue is that AC is more efficient, reason is alternators big and small rectify the current to pulsating DC via a bank of diodes, these diodes generate significant heat, and heat takes enormous power to make, so its wasted power.
Now to be honest I don’t understand how a modern battery charger turns AC into DC, but they do it with very little heat, and are extremely precise and good ones are almost infinitely adjustable.
Then you have the problem of running a massive inverter, inverters sized for the load can be up to 95% efficient, which is very, very efficient, but if you run a huge inverter, you lose in efficiency, and it’s surprising how much you lose.


There is nothing magic about running AC off of a battery bank, it’s just a load that is orders of magnitude larger than the average cruising boat has though, so you need both a rather large source of power, and a large bank to store it, but is really just a problem of scale, that’s all.

In my opinion, first it’s gonna take big $$$, now way around that, but if your so inclined to go this route, your better served by an AC generator, reasoning is they are mainstream, everybody has parts and is familiar with fixing them, and replacements are everywhere, and converting to DC is no big deal anymore, in fact or used to be that you were either AC or DC, but now it’s so easy to convert back and forth, with good efficiency, that it really doesn’t matter.

Take the little Honda inverter / generator as an example, not too long ago if you had proposed that idea you would have been laughed at. But the little rascals make extremely accurate power and do so with good efficiency, in fact my Honda’s power is more stable than my built in Diesel. The little Honda is always dead on 60 Hz, and voltage is always between 120 and 125 VAC.

[a64pilot]

I’m just surprised that the inverter / generator hasn’t been scaled up to built in gensets, that is I think the future.
http://www.arrl.org/files/file/QST%2...einschmidt.pdf

[bluenomads]

Have a look at Eniquest. Australian. We're seriously thinking of their 16kW one.