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Old 11-07-2013, 09:44   #1
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Can wind + solar ever offset AC power?

It's my understanding that wind and power generation on a cat can definitely help offset the draw of things like: hot water heater, navigation, lights, kitchen, electrical outlets, winches, heads, etc...

(NOTE: AC below means "air conditioning")

But once you turn on the AC you *MUST* run the gen. There's simply no way to store enough energy in the batteries to run the AC for any length of time.

Or are we getting close? I mean, can there even be a situation where you can get an extra hour or two of AC running just off the batteries? Do any figures get within the ballpark?

I ask because on a recent charter I found the generator noise violated the peace and tranquility of moving under sail. IE., it sounded like we had a small motor running when in fact the engines were off (except for the genny of course). I really enjoy hearing (and feeling) nothing but the boat.
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Old 11-07-2013, 09:49   #2
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Re: Can wind + solar ever offset AC power?

SHOT OFF THE AC.

We have never used the AC in the BVI on any chart boat we have been on.
Nice breeze when on moorings.
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Old 11-07-2013, 09:51   #3
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Re: Can wind + solar ever offset AC power?

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Originally Posted by Cotemar View Post
SHOT OFF THE AC.

We have never used the AC in the BVI on any chart boat we have been on.
Nice breeze when on moorings.
Ok, but for other parts of the world where you DO need AC from time to time ...
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Old 11-07-2013, 09:58   #4
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Re: Can wind + solar ever offset AC power?

You can run the new Smart Start style A/Cs off a decent battery bank. You will need to charge it up daily so a really good size solar and/ or wind setup is required. Easier on a cat because of that big coach roof. So, the answer is yes.
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Old 11-07-2013, 09:58   #5
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Re: Can wind + solar ever offset AC power?

If you have a big battery bank, 800+ AH, then you can run a small AC off of an inverter to keep your sleeping berth cool overnight. But then you have to run your genset for 4-6 hours to recharge your battery bank the next day.

If you have a real big solar array, say 1000 watts or greater, you might be able to recharge those batteries during the day just with solar.

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Old 11-07-2013, 10:08   #6
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Re: Can wind + solar ever offset AC power?

Unless you are the type that think their boat is floating condo, should be no problem. Limit your ac appliances as inverters have internal losses that make them less than ideal. Not really a problem as very few things require ac and most of them for relatively short duration. Some areas like the PNW may be chancy because of a lack of sun and wind but the usual cruising areas are not a problem. As in all things in off the grid electrical living, train yourself to keep your electrical use under control.
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Old 11-07-2013, 10:18   #7
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Re: Can wind + solar ever offset AC power?

I've run AC off of batteries and a major drawback is the type of batteries. Lead acid and the Pukert effect under heavy inverter draw de-rates the capacity. So a robust 800 a-hr bank has about 1/2 that capacity. LiFePO4 cells do not sag or de-rate under heavy loads and will produce their rating and still have 20% left over.

The math

800 a-hr lead acid drawn down to 50% DOD = 400 a-hr plus Pukert maybe 250 a-hr.

800 a-hr of LiFePO4 at 80% DOD = 640 a-hr.
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Old 11-07-2013, 12:07   #8
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Re: Can wind + solar ever offset AC power?

The AC Units on my cat draw 15 amps@120v for 1 and about 26 amps for both. The water pump runs both units so the draw is less than 2x for both. So assuming you can live with one unit at night and it runs at a 50% duty cycle for 8 hours or constant running for 4 hours. The inverter requires roughly 10 amps at 12V for every 1 amp at 120V so to run one ac unit requires 150 ah at 12V per hour or 600 ah per night. Assuming no other usage you would need about 1500 ah of lead acid batteries or about 800 ah of lifepo4 batteries. The reason I state 1500 ah for lead acid is that you can really only cycle them practically from 50-85% on the genset because the charge rate drops so dramatically above that you are wasting a huge amount of diesel and even more time to attempt to get them to 100%. About the best battery charger you can get for a small cruising boat is 150 amps and it will take all day on the genset to get it to 100%. Due to inefficiencies you would probably need to think about putting about 650-700 ah back in to the batteries or nominally about 5000 watt hours. Since the sun doesn't always shine I have found that one can count on getting about 50% of the rated ratings for about 6 hours per day or less. So for 5000 watt hours you will need about 833 average watts per hour at 100% efficency or 1666 watts of solar panels at 50% efficiency. That is a lot of solar panels. I know one goy with a ST Francis 50 and he has 1200 watts and that covers almost all of his hardtop. You would need a really big boat for enough room to run one small AC. You could of course use a combination of devices to reduce the solar panel requirement. You could for instance run your genset for 2 hours and reduce the solar requirement nearly 50% with the proper battery charger. The genset will not be taxed by a 150amp battery charger so you could split the battery bank in two while charging and effectively charge twice as fast with a second charger. Wind generators might help some, but their output is pretty low at most normally experience wind speeds. They really don't start cranking out lots of power until the wind is in the 20s. Some of the best put out about 10 amps in 15 knots of wind and if that ran 24hrs per day you would put a 240 ah dent in your 700 ah requirement for AC, with two, 480 ah. The problem is that the nights you really need AC are hot and still and the wind generators will not be putting out anything.

Good luck
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Old 11-07-2013, 12:37   #9
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Re: Can wind + solar ever offset AC power?

If you were serious about it, the best option would be a 12/24v system that doesn't rely on an inverter. Glacier Bay's "DC Breeze" is the only system I know of built for this. You would get longer run times, of course, with a 24v system than with 12v.
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Old 11-07-2013, 12:37   #10
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Re: Can wind + solar ever offset AC power?

A/C while sailing? Heaven forfend.
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Old 12-07-2013, 03:11   #11
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Re: Can wind + solar ever offset AC power?

If one really wants to generate that much electricity without burning hydrocarbon fuels, regenerative operation with an electric propulsion setup would seem to be the best option.
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Old 12-07-2013, 16:45   #12
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Re: Can wind + solar ever offset AC power?

I was in the same boat you are in (not really in your boat) I was heading on a long trip from Florida to Carb and wanted to run A/c at night. For all you non A/C hardcore popeye sailers, go to bahamas this month and try to get a good night sleep in 85 degrees with no see ums biting the hell out of you with no wind. I knew A/C was a must, anyway I tried many options, 3 solar panels and win gen. Inverters. After many failures I ended up using a Honda 2000 gen. carry on and lil red was just the ticket. It was so quiet at night I was worried it got stolen on some nights. I chained it up at night to solve this problem you can get one for about 1000 dollars which is a lot less that you are going to spend on solar and inverters. 2 and 1/2 years and that gen started everytime on the first pull.
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Old 12-07-2013, 20:50   #13
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... because you put it outside at the other end of your boat...
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Old 13-07-2013, 06:28   #14
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Our new boat is being set up as 48 volt due to the hybrid system. I believe that cuts down considerably on the amps used...correct? With 1000+ watts of solar and hydro generation under sail I am hoping for as little diesel charging as possible. We rarely use AC in our home and hope to use it even less when living aboard, but as one post said there are just some nights when it's unbearable.
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Old 13-07-2013, 06:49   #15
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Re: Can wind + solar ever offset AC power?

Quote:
Originally Posted by bryguy67 View Post
Our new boat is being set up as 48 volt due to the hybrid system. I believe that cuts down considerably on the amps used...correct? With 1000+ watts of solar and hydro generation under sail I am hoping for as little diesel charging as possible. We rarely use AC in our home and hope to use it even less when living aboard, but as one post said there are just some nights when it's unbearable.
As the voltage increases the current goes down, but the watts remain the same.

Bulding a boat always exciting, but there are a lot of decisions and compromises to made. The performance of the solar panels and the hydro generation should be quite predictable. Using some simple scenarios you should be able to ascertain how much of the time diesel charging will need to used under various conditions.
It may be worth getting the boatbuilders to do these calculations.

Understanding the likely performance is important in choosing equipment (cooking, solar panel size, battery type and capacity etc) wisely.
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