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Old 08-11-2013, 12:21   #1
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Theoretical Power Supply

I know this has been asked and answered 10 times already but excuse me because I don't know how to find it.
What is the actual (average) amount of power that can be generated on a daily basis, assuming four large Solar panels (undefined as I'm not yet knowledgeable enough to specify, but assume cost effective panels), a wind generator and running the engine for an hour or so a day, assuming again a cost effective max amount of alternator, or alternators ?
Another assumption is there will be enough battery bank there to absorb whatever can be generated, enough hopefully to absorb a higher than normal sunny / windy day to fill in for the opposite.
location will be + or - 30 latitude, and vessel will be continously occupied.
Is there anything else needed that I have left out

On edit, I don't think adding up the claimed power output of the components will get me there as there have to be considerable losses, losses that I can't come up with without experience.

I'm trying to come up with a swag of a total amount of electrical power I will need for this theoretical case, point being is it reasonable to eliminate the need of a generator, or said possibly another way at what rate of electrical consumption does it just simply make more sense to have a gen set?
A small gen set like the little Honda 2000i is also another possibility ti fill in for several overcast or days of no wind
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Old 08-11-2013, 13:10   #2
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Re: theoretical power supply

I planned my electrical usage base on bank size, alternator out put and how long I plan to run the engine each day. Any solar or wind I get just saves fuel.
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Old 08-11-2013, 13:22   #3
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Re: Theoretical Power Supply

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Originally Posted by a64pilot View Post
......................What is the actual (average) amount of power that can be generated on a daily basis, assuming four large Solar panels...... wind generator and running the engine for an hour or so a day ...............
I'll stay away from actual numbers too; however, these sources of power can typically allow you to use modest lighting (certainly LEDs), fresh water pump, light communications (charging Ipad, etc.) and the Big Pig! The "big pig" is the refer/freezer, but this is also possible with an efficient unit with something like a Danfloss compressor and small fan w/air heat exchange. The things that will not be supported would be constant/intermittant water pumping for heat echange such as some refrig/freezers; air conditioning; electric heating or cooking.
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Old 08-11-2013, 13:42   #4
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Re: Theoretical Power Supply

I think you're going about it backwards. Start from what electrical devices you are going to have, multiply how much current they use by how long you'll have them on. That will tell you how much power you need to generate.
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Old 08-11-2013, 13:48   #5
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Re: Theoretical Power Supply

There's no way to answer your question. "Large" is way too vague to get any idea of what sort of wattage could be expected from four "large" solar panels.

Wind generator? What kind? What size? Hung where?

Alternator? What size? How big is your engine and how fast are you running it?

I'm sorry, but there is just no simple "rule of thumb" that you can use here. First you have to figure out approximately how much electricity you need--just get an average and it could be ridiculously more than you'll ever use, or drastically less. Then you need to figure out how much electricity you can generate--depends on your alternator, space for solar panels, etc. You're going to have to do some homework, and do some basic calculations.

Or just get as big of a battery bank as you can, and as many solar panels as you can fit. Then hope that your system is neither so over-sized that you spent way more than you needed to, nor so under-sized that you will have to run your engine constantly to keep up.

Those are your choices. Good luck.
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Old 08-11-2013, 13:56   #6
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Quote:
Originally Posted by cal40john View Post
I think you're going about it backwards. Start from what electrical devices you are going to have, multiply how much current they use by how long you'll have them on. That will tell you how much power you need to generate.
You have an excellent point, however if I can figure out how much power I can make, think of it like money and this may make more sense, then I can determine how much I can spend.
Then there is, at how much power demand does it make more sense to go on ahead and reconcile myself to a generator as opposed to trying to do it all with DC?
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Old 08-11-2013, 14:03   #7
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Re: Theoretical Power Supply

This is a hard question to answer since there are so many variables. Every boat is different. Every crew has different consumption habits. I think the right progression is to start by figuring your consumption estimates, then size your bank and charging capability to match your needs. In general, I think redundancy is a good thing. Over-size where it makes sense. A truism I hear frequently here is that you can’t have too much power.

Here is our rig.
100 amp Balmar alternator. Output practically is only 75-80 amps max.
Air Breeze wind generator. Obviously output widely varies. We hope to get avg 4 amps/hr = 100 amp/day
2X 135 watt Kyocera panels/25A Blue Sky Cont. Assumption 90 amps/day
Honda 2000 generator. Used often last time out. Keeping it just for backup now.
800 AH AGM bank. 400 AH useable capacity

My planning estimates are that we consume 200AH per day on the hook. Half of that is the fridge and freezer. My expectation is that we’ll be almost 100% self-sufficient at anchor with just the wind and solar. It should be at least 3-4 days before we would have to run something to charge batteries worst case, which is OK since we’ll probably be underway at that point anyway. Under way usage would be higher of course given use of the auto pilot and nav electronics.

The Air Breeze and solar Panels are new this year. We’ve had some test weekends on the hook this year where they have really given us a good indication of the output. I am really looking forward to actual output over time that I can report. We’ll be heading out in a few weeks for the Bahamas.

To directly answer your question, I think the low cost of solar today would totally eliminate the need to spend 10K on a built in generator if you don’t already have one, assuming you have the real estate for enough solar. The wind generator is not as cost-efficient as solar, but we felt that having both gives us more flexibility. I like having the Honda as a fail-safe, since it is far less expensive to purchase and install and a built in genset.

Hope this helps.
Scott
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Old 08-11-2013, 14:18   #8
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Re: Theoretical Power Supply

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You have an excellent point, however if I can figure out how much power I can make, think of it like money and this may make more sense, then I can determine how much I can spend.
Then there is, at how much power demand does it make more sense to go on ahead and reconcile myself to a generator as opposed to trying to do it all with DC?
OK, here are 305 watt solar panels, at a $1 per watt is an efficient price.
Astronergy CHSM 6612P 305-watt solar panels

Using rule of thumb 4 hours per day, for 4 panels that's 400 amp-hrs in a day, add a 270 amp alternator that we'll say you run for an hour while the huge battery bank is depleted and you could get 270 amp-hrs from that.

Do you have room to mount 4 over 6 foot by 40 inch panels where they won't be obscured by the sun? Do you have an engine that can take the side load or drag or space of the big alternator?
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Old 08-11-2013, 14:33   #9
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Re: Theoretical Power Supply

I figured three scenarios for power consumption. The first was actual sailing - Autopilot, lights, radio, etc. The second was living at anchor and the third was with the boat on a mooring unattended.

I measured everything electrical on my boat. With some equipment it was a measurement at idle or easy running and also while working hard (AP and reefer as examples. Radio transmit would be another). The rest, with lights as an example, was easy (Chotto is 100% led). In the end I also added a 15% error factor for each scenario.

What that did was tell me what battery capacity would be optimal, the charging cycles of my current arrangement (very good but not perfect - never is) and lastly helped me determine sources and quantity of power generation.

Now that I have that info, I'm in the final process of selecting power generation. I currently have a 5.5kw genset that I don't want to run all the time so I'm going with a few solar panels to meet a good chunk of my need.

While under sail, the highest usage due to the autopilot (I don't do enough long long distance to warrant a wind vane), radar, etc is met by the solar and running the gen for about 2 hours a day. At anchor the solar will meet most of the need and the gen would be on occasion or as needed. Unattended the solar will handle it all.

So long story.. Measure what you have and plan from there.
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Old 08-11-2013, 14:46   #10
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I don't have anything yet, I'm looking and wanted to know if having a genset is a big plus or not, currently at least on paper what looks like a good boat for my needs does not have a genset, I'm flying down to Ft. Pierce this weekend and looking at boats there. Boats that I am considering go from not having a genset to having a 20KW gen. Those are two extremes of course. I'm thinking I can do without one and have a little honda to run the watermaker and be a back-up for power if needed. I don't like having to have gas on-board, but I guess I pretty much have to anyway for the Dinghy. Plus the little eHonda can be had for a grand so even if I had to replace it every couple of years that would be OK too.
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Old 08-11-2013, 15:52   #11
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Re: Theoretical Power Supply

You can see from the posts above why I did not give you a numerical answer. As others have said, you have to provide numbers to receive numbers. Still, what you propose is feasible if you keep your needs simple.
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Old 09-11-2013, 02:08   #12
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Re: Theoretical Power Supply

Perhaps someone does need to quote figures just to help the OP. Here are my suggestions - shout me down if you wish.

All boats are different, BUT you can take a guess for the average liveaboard and say that the fridge is the biggest user followed by the computer. So why not go for 150 Ah usage per day. Less maybe at anchor, more when sailing.

So the MINIMUM battery bank capacity should be at least 400Ah. With that you need a MINIMUM 100 amp alternator and external SMART regulator.

To replace 150ah/day in the summer months multiply by 3 = 450 watts of solar. if you are permanently on board for most of the year multiply by 4 = 600 watts. This is impractical for most monohulls so you could add a high output wind genny or some kind of generator or motoring between anchorages to top up. If you add air con and other AC loads, like a watermaker, then a built-in 4kva genset would be needed. With a big AGM bank then a DC genset charging at 280 amps would be a good option. Add a 3Kw inverter for anytime AC.
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Old 09-11-2013, 09:32   #13
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Perhaps someone does need to quote figures just to help the OP. Here are my suggestions - shout me down if you wish. All boats are different, BUT you can take a guess for the average liveaboard and say that the fridge is the biggest user followed by the computer. So why not go for 150 Ah usage per day. Less maybe at anchor, more when sailing. So the MINIMUM battery bank capacity should be at least 400Ah. With that you need a MINIMUM 100 amp alternator and external SMART regulator. To replace 150ah/day in the summer months multiply by 3 = 450 watts of solar. if you are permanently on board for most of the year multiply by 4 = 600 watts. This is impractical for most monohulls so you could add a high output wind genny or some kind of generator or motoring between anchorages to top up. If you add air con and other AC loads, like a watermaker, then a built-in 4kva genset would be needed. With a big AGM bank then a DC genset charging at 280 amps would be a good option. Add a 3Kw inverter for anytime AC.
Thank you , this is what I was looking for
See as I'm sure you know dual 180 amp alternator kits driven by individual serpentine belts exist. Yes this would be quite a draw on the engine, but assuming a 4 cyl Yanmar Diesel above say 85 SHP, this should be achievable, may have to re-prop for cruising, I don't know. I also don't know what the duty cycle of a 180 amp Alt is, I assume due to heat build up, it's not 100%, but if you could get 300 amps from a dual 180 amp Alt set-up, that's a little over 4KW. Now I don't know if that's realistic or not, but if you got only 200 amps from a dual 180 amp set-up, that's almost 3KW. I believe 100 amps from a 180 amp Alternator may be do-able. I don't have the experience, so I don't know.
This is to replenish what the wind and solar can't of course, and possibly run that AC if necessary during really hot days.
OK, why won't this work? I'm sure there is some obvious thing I don't see, what is it? With serpentine belts and dual Alts mounted on either side of the engine, the crank bearing should have no problem, I bet it's not the load I have on my truck with it's dual alts, power steering pump, air conditioner compressor and radiator fan, and it get's by one one belt.
I would also assume you want / need to put a load on a Diesel to prevent stacking and dual Alt's would do this too.
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Old 09-11-2013, 09:57   #14
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Re: Theoretical Power Supply

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..... I believe 100 amps from a 180 amp Alternator may be do-able. I don't have the experience, so I don't know......
You need "hot rated" marine alternators that will give you close to what they are speced at. Don't use automotive alternators that are designed to charge starter batteries not deep cycle batteries.
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Old 09-11-2013, 10:12   #15
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When I get here I will buy one of the kits from Balmar or others, I would stay away from anything automotive, sometimes there is a difference between a marine component and an automotive component, even if they look the same
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