Diesel-Electric Power system on a Ship

[GreyBeaver]

Hi, I'm looking to create an entirely offgrid power system on a very large boat, using a (Bio)Diesel-electric generator and maybe a windmill and submerged generator, as well as some solar but not solar-electric so it doesn't bear mentioning.
I'm kind of new to this, so I was wondering what exactly I would need to get everything working properly, and how much power would we typically need for about twenty people for a self-sufficient vessel?
I'm not really sure where to start, and trying to piece it together by myself might result in missing some parts or something drastically unfortunate like that...

 

[russ_watters]

Hi, I'm looking to create an entirely offgrid power system on a very large boat, using a (Bio)Diesel-electric generator and maybe a windmill and submerged generator, as well as some solar but not solar-electric so it doesn't bear mentioning.
I'm kind of new to this, so I was wondering what exactly I would need to get everything working properly, and how much power would we typically need for about twenty people for a self-sufficient vessel?
I'm not really sure where to start, and trying to piece it together by myself might result in missing some parts or something drastically unfortunate like that...

We need more info - if that's propulsion, we need the size of the boat (better yet, if the boat already has a motor, just use that size). Then you need equipment specs: air conditioner, radar, refrigerator, etc. to calculate the loads.

Windmills can be bought retail for charging batteries. Screw-turbines (I presume for when at anchor?) would need to be designed from scratch.

edit: maybe I'm missing something actually: most larger boats already have all this stuff. What exactly are you planning on doing differently? Diesel-electric propulsion? Why? It likely won't improve overall system performance or efficiency.

 

[GreyBeaver]

uhm...you don't understand
this has nothing to do with propulsion...at all...
that would be a different matter entirely...
I just need a power system for twenty people.
I need to know all the components I'd need to do this.
I'll probably have to add up the draw of every electrical device onboard to decide on a generator, but opinions and experience on what that many people might draw would be appreciated.

 

[NateTG]

An important factor to consider is what type of power you want to be running. Two naturally appealing choices are 12/24 Volt DC which is nice because it works with Lead/Acid and normal motor electric equipment and is also somewhat less hazardous in a wet environment , and 110 volt AC which is much easier to find appliances for. That's a descision that can drastically affect your needs.

Once you've figured that out, you can try to determine your power needs. You should have the good sense to have some kind of fuel based heating and cooking, but refrigeration will probably be one of your big power eaters. A big part of the power needs depend on what you what kind of lifestyle you're looking for on the boat.

Depending on how much power you're using things can get more or less complicated. If you're looking at the 12/24V solution, then essentially, you'll be ok with a battery bank, chargers, fuses, and wiring. The 110V solution requires an inverter or inverters. As you increase the power consumption, you'll want to get more sophisticated. There's a website from a guy who built his own 10KW UPS system that would probably help you out a whole bunch.

 

[Ivan Seeking]

Cost may drive many of these decisions.

For example, depending on the total power output needed, low volt motors can get big, heavy, and expensive. Using 12 or 24 volts for fractional HP applications is usually fine but the same is not true for a 20 HP application. Depending on the equipment that you wish to run, say for example a large air conditioning and heating system, or a large freezer, you might even want to consider a 208 VAC, three phase generator. You can then run a wild leg configuration, that is each leg of power can be run across a load directly to neutral, instead of to another leg of power. This yields 120VAC for standard appliances - though the load for each phase needs to be approximately the same. The higher voltage 208 VAC and three phase power is then available for large appliance loads and large motors. This can greatly reduce cost and size. Three phase also allows naturally for reversing AC motors which can sometimes come in handy.

 

[GreyBeaver]

If possible, I'd rather stay away from hazardous high current situations. There shouldn't be any need for applications bigger than maybe a window air conditioner. Standard house current should be fine, unless going with DC would be cheaper and more efficient.
I've seen a good deal of DC appliances that claim to be very energy efficient, but something tells me I should really go for AC house current instead. Just seems like it would make things a whole lot simpler.
What would I need to get a system like this up on a ship?
And how big of a generator should we need?

 

[Averagesupernova]

I would use AC ONLY for what you need it for. DC is easily stored in batteries. For AC you can use an invertor (lossy) when it is not feasible to run a generator.

 

[Ivan Seeking]

Your first order of business seem to be a list of what you plan to run.

Also, AFAIK, inverters are up to 95% efficient these days.

 

[Ivan Seeking]

Also, an interesting note on lead-acid batteries: The charging efficiency is classically considered to be as good as 95%, however this assumes deep cycle charging which is not how lead-acid batteries are often applied. It turns out that in practice, if for example the battery tends to operate with a minimum of an 80-90% charge level, then charging efficiencies might, on the average, be as low as 55%. Here is one paper on the subject.

http://www.sandia.gov/pv/docs/PDF/batpapsteve.pdf

for an HTML format

http://216.239.41.104/search?q=cach...teve.pdf+"battery+efficiency"+&hl=en&ie=UTF-8

 

[Cliff_J]

High voltage is far more hazardous than high current. Also, high voltage can be more efficient since the wiring needs drop tremendously (for high current the energy lost as heat in the wires is by the square of the current) so it has its advantages.

A windmill implies you will use a battery to store the power generated. Thus you will need the windmill generator, a charge controller to charge the batteries, batteries, and an inverter to run any AC accesories off those batteries. The solar panel generates electricity in the same way, don't understand why you wouldn't consider it as well. Both can be expensive and a bit cumbersome.

Also, if you are going to be using batteries, you also might need a sine-wave inverter if you would ever need to run a TV or radio and would not want the noise from the inverter picked up by an inexpensive unit. Obviously a 12V DC operated unit would not suffer from this, but 20 people could dictate a television larger than is available in a 12V size. Here's a couple links that outline some parameters for you:
http://www.eere.energy.gov/consumerinfo/refbriefs/bb8.html
http://www.absak.com/alternative_energy/acdc_inverters.html

Cliff

 

[GreyBeaver]

Thanks You! ^_^
The reason I'm trying to stay away from solar electric is because solar cells can suffer extreme degradation, and since it is not a mechanical source they would be extremely hard to repair if damaged, and in many cases they need to be replaced every few years. They are also very expensive, and having to replace equipment that expensive, that often, and that complicated, is just not worth the effort. At this point you might be thinking of explaining in depth the simplicity of solar cells, but I just feel that something more mechanial would be better, that's all...

Thank you for your suggestions, I was originally thinking about a DC system, but wasn't quite sure if it would work out, and I would assume that the computers and control room equipment would need to have an AC inverter, which leads me to thinking of either having them on a separate system, taking charged batteries directly to an inverter there and avoiding the rest of the system entirely...actually, that sounds pretty good, I guess I won't even bother with a second option, hehehe...
Is this the case? I will need a separate AC system to run computers and navigation equipment off of? Obviously, this question is for people with somewhat specific experience, but I assume that a computer is better off on an AC current than DC. It's like trying to put diesel into a gasoline engine, right? Not a good idea...

 

[Averagesupernova]

Greybeaver, I think you really need to study about electricity and electronics before you can make generalizations that a computer is better off with AC than DC or anything for that matter. True, you can't necessarily hook up 12 volts DC to the computers wall plug, but there ARE DC power supplies available for computers. The question is deciding what is worth doing. Which way is more efficient? Does it warrant the extra cost? No one else but you can decide that. I would recommend running as much as you can off of DC, invertors get expensive in a hurry when you get into high power. I don't know what you are doing for refrigeration, but there are alternatives to electric with that as you may well know.

 

[Cliff_J]

Given that a few people are putting computers in their cars, a DC-DC switching power supply designed to run a computer off a 12V battery is available. If designed correctly, it would be the most efficient way to power a regular computer from a battery.

Technically, the computer has a power supply inside of it that converts the AC into DC that the computer runs on. However, it does it in a very controlled fashion so the computer doesn't burn up. Gasoline in a gas engine, diesel in a diesel engine - use whatever you got or buy the appropriate one for your task! :)

For the navigation equipment, look at the needs in terms of the current required, it will tell you how big an inverter you need.

Then, you need to figure how long the batteries will last. This is a two-sided sword, as you can run the batteries from 100% charge down to say 20% capacity but in doing so they will only last a year or two (assuming you keep them well charged when not used). If you only used them from 100% charge down to 70% then they will last more than twice as long, but you need a lot more batteries!

There are a few websites out there that detail what's needed to setup an alternative power system based on batteries (and batteries are the only way to really use wind or solar since they only work for a few hours a day and you need to store the energy when they make it). You may want to read into this more, it gets really expensive quickly. I'd like to put it in my house, but it would take about 15yrs to recoup the investment assuming the electrical bills go up by inflation, without that increase the switch would not pay for itself at all but cost more than just buying the electricity!

A gas/diesel generator can go quite a while on just a few gallons of fuel, and you can refill it very easily. Waiting for a battery to charge so you can find your way home on a day with no wind doesn't sound like a good idea if the wind turbine is the only source.

A good plan with exact numbers of usage with margin of safety would be a start, and then contingency plans (the what if all this don't work for X or Y reason) would be nice too before even thinking of leaving terra firma.

Cliff

 

[russ_watters]

GrayBeard, most of the stuff you want to do: windmills, a/c, lights, gps, radar, computers, etc. are all off-the-shelf components and already being done in boats all the time. Any decent boating supply store will have most of what you need. Try HERE.

FYI, most nav equipment is both 12VDC/115VAC. You may actually want to run 12V to the chart table and 115V everywhere else.

 

[GreyBeaver]

I didn't say I was doing something new, hehehe...
I just said I need help doing it ^_^

 

[russ_watters]

Well, I'm a champion conclusion jumper... sorry.

 

[wj]

Here is a web page that will tell you everything you need to know. It pros and cons AC/ DC, helps predict energy requirements, gives avg energy drain of appliances, and has lots of good information on battery and generator care.

http://www.cosolar.com/system_design/yourself.htm

Also
Solar panels are not the only way to get energy from the sun.
You use the heat to expand air inside a sterling engine, which can then drive a generator. This method is much cheaper, stronger, and more efficent than solar panels. If it breaks you can fix it yourself.

There are plently of diagrams and plans online. Just search for "sterling engine" on google.