AC or DC (both?) For the Small Seastead/Homesteader Philosophy

(Bob LLewellyn) #41

[quote=“M.Bas, post:39, topic:2591”]
The only real adapvantage AC seems to have is massive base of consumer/retail appliances dominating the market[/quote]
The real advantage of ac is that it is easy to convert from one voltage to another and higher voltages will be able to be transmitted over a long stretch, dc requires large cables to go just a short way. A problem with using converters is that most converters use a square wave pattern instead of a true sin wave. Your blender and mixers won’t show a difference but computers might. There are true sin wave converters but they are expensive.

For cooking a lot of boaters use propane, butane, and I have heard of the possibility of using methane but I wouldn’t have a clue as to where to buy it. Tying air conditioning to heating like they do for heat pumps on land doesn’t make a whole lot of sense out at sea. The water is cooler than the air at sea so using a heat pump would use more energy than to pump the cold ocean water through the lines and using fans.

Because of the higher humidity, higher voltages are a little more hazardous at sea but not so much that you couldn’t compensate for it. But for the few times that you want AC 120V you could run a small generator for the time that you needed it. Remember if we use diesel made from seaweed and algae, we are using a renewable energy source. Electricity is not the only renewable energy source. We could also make hydrogen from the seawater using dc energy then burn the hydrogen as a renewable energy.

Also remember that a homestead at sea won’t need somethings that a homestead on land would need. The northern Caribbean can get chilly in the winter. You may even need a warm jacket if you are out in the wind at night but it never gets really cold. We had a space heater for our boat but never used it. At most I needed to put on a long sleeve shirt, and that was further north near Florida.

Marinea is intended to be a full service marina so we will need to supply 120V, propane, gas and diesel.


Right now, around the world, people are making their own biogas, using food wastes. This, in turn, also yields a high value, organic liquid fertilizer suitable for hydroponics, aeroponics, and other similar food production methods, as well as direct application in gardening. Often, the quality is such that it should be diluted.

Hydroponics and aeroponics are proven to us ~1/10 of the water that conventional farming and gardening use.

Point being almost free fuel from readily available waste-streams is sustainable. Upgrading Biogas to Methane is simple enough. As a fuel, it can be used for heat, cooking, hot water, electricity generation, etc.

Methane is also produced from sewage treatment.

However, using electricity, the single, most efficient use of electricity is resistive heat. It is easy to get 98% of the energy put in, back, as heat.


You can hook up all the batteries in series you want, but you’re still limited by the voltage rating of the consumers if you don’t want to add converters. A Tesla Powerwall battery pack seems to be operating at 50VDC so if you don’t have any 48VDC or 50VDC appliances you will still need either a DC/DC or DC/AC converter.

When talking about small scale homesteading/seasteading converting between AC voltage levels is not relevant. So that advantage is also not relevant. The moment it becomes relevant you’re not talking small scale any more and you are using a serious amount of power. The cable lengths you can expect on a small seastead are the same you can expect in a home, you’re not trying to power something a mile away, so even for DC cable sizes would be ok if you don’t have heavy consumers on DC.
Inverters you should always buy pure sine wave inverters, even thinking about using a modified square wave should be frowned upon.

Propane, butane, methane, LPG, gas, diesel you probably need to go out and buy it somewhere.
Solar, wind and wave can be done onsite and thus would have my preference.
On ships chilled and heated water are tied into the air conditioning system with often a resistive heater in the fan coil. Water in the tropics can’t really be used to pump through some lines and use a fan to cool a room, the water temp is too high. Water in the arctics can probably be used for that purpose, but you probably have more need of heating in those areas.

I would recommend having an emergency generator present any way, and it can be your system philosophy to run a generator every time you need to use one of the heavier consumers.
Generating DC to make hydrogen, store it and convert it back to electricity or burn it is just a bad idea efficiency wise.

Marinea doesn’t really count as small now does it?
A small seastead to me is basically a single homestead on a barge, maybe a couple of them together but all of them self sufficient energy wise.


Home scale biodigesters can be made using 55 gallon drums, for 1-2 people, and IBC tanks for larger homes.

It is possible to have a seawater based digester, using kelp for the biomass, as well, in order to reduce the demand for freshwater.

~1 cubic meter of biogas will cook 1 meal for a family of 4.

While I haven’t checked, it may make it feasible to inhabit such places as the Sargasso Sea. Grow and continually harvest your own fuel…? Natural Gas is usually 80%+ Methane, with Butane, Propane, etc., making up the rest.

Biogas is something I have studied, off and on, for about 40 years.

DC can be regulated down, the same way an automotive charger regulates 12-15 VDC to charge devices via USB ports, with minimal losses. Many of those same chargers are also used with aircraft electrical supply at 24-28 VDC.

Research your options, before locking in on one ‘perfect’ solution. Often, as with a typical household, multiple energy sources are more practical, than a single source.

(Bob LLewellyn) #45

[quote=“M.Bas, post:43, topic:2591”]
Water in the tropics can’t really be used to pump through some lines and use a fan to cool a room, the water temp is too high.[/quote]
You have been there then?


Sorry, using my phone…
Pointing out along WITH your response

For the use of ocean thermoclines to generate energy, see Ocean thermal energy conversion.

Graph showing a tropical ocean thermocline (depth vs. temperature). Note the rapid change between 100 and 1000 meters. The temperature is nearly constant after 1500 meters depth.


Nope, I’m not really suited for warm weather. I prefer the colder climates.

For example the water temperature for the Bahama’s is 22C to 28C according to the official Bahama’s website. If you could just simply pump water of that temperature through the HVAC system ships wouldn’t need massive chilled water compressors to cool the water down to usable levels.

But HVAC isn’t my area, I’m an electrical guy. So I won’t be able to give more info other than that if it would be possible it would be used instead of big expensive chillers.

(Bob LLewellyn) #48

[quote=“M.Bas, post:47, topic:2591”]
if it would be possible it would be used instead of big expensive chillers.[/quote]
That may be true for boats that move around a lot but not for a stationary structure that can use a use deeper source closer to the thermocline. Actually it is believed that if you could bring water from below the thermocline to the surface, it would instantly freeze because it is only the pressure of the deep ocean that keeps it from freezing where it is. Saltwater freezes at 28 degrees (-2 Celsius) on the surface.


A small seastead will not have the resources to get water from those depths. Most seasteads won’t even be located in such deep waters in the beginning. What are your ideas of a small seastead as mentioned in the topic title?


Me? I’m all FOR small seasteads and sea-farming. My goal is within Texas State waters, still over the continental shelf. Slip a weighted hose end over the side, use attached floats to minimize strain, and lower it to near the bottom. Simply use an electric pump to draw cooler water up from depth, for most cooling purposes, collect condensation as clean, pure water, for the drinking supply, as well.

Given a chance, I’d like to build larger than the one cabin hull I want as a first attempt, and have a greenhouse that also makes fresh water, while having space to raise ordinary foods, using hydroponics and aquaponics. Other additional space would allow for an IMTA sea farm, and processing.

(.) #51

Let others join the conversation
This topic is clearly important to you – you’ve posted more than 30% of the replies here.
Are you sure you’re providing adequate time for other people to share their points of view, too?

So I really do not want to lock others out. Yeah, sure. You guys go for it.

(Bob LLewellyn) #52

[quote=“M.Bas, post:49, topic:2591”]
What are your ideas of a small seastead as mentioned in the topic title?[/quote]

A home base barge 385 ft long 85 ft wide with about a hundred boats or so.


Anyway, I didn’t mean to sound carried away on biogas, just that there’s no reason to discount having multiple energy sources and one that is renewable makes a lot of sense, to me.

Back on topic:

… and a good pdf with sound reasoning for DC in buildings, though aimed at office buildings, the info still applies…


Not really small in my opinion, that’s the size of a small cruise vessel and with the 100 additional boats it’ll have the population of a small cruise vessel. I can give you some numbers regarding the electrical needs from a cruise vessel that size if you’re interested.

(Bob LLewellyn) #55

That might be good for comparison and a starting number to begin with if it isn’t too much trouble that is…However separate boats will have a different usage than where everyone is on one ship but it should still be useful. Thanks in advance…


BS. That is exactly what ELWA did for their radio station in Monrovia, Liberia.

Simple heat transfer. Water cooler than the air … heat in the air transfers to the water, and the air is consequently cooled.


Which explains why all the experiment kits for children use AC and DC interchangeably.


Oh … wait … no …

… DC is much safer for the untrained who, nevertheless, want to experiment with some simple ideas about how to use electricity in the context of seasteading.

Which is why we let young kids hook batteries up to DC light bulbs without adult supervision, but prohibit them from experimenting with old AC desk lamps unless they have trained adult supervision.


If you are referring to the generator cooling setup that can be found on the internet, that’s a completely different thing. Cooling a generator with water over 30C is absolutely no problem, trying to cool a room using the same setup is not going to work.

I’m pretty sure that has more to do with the voltage level, not AC vs DC. You wouldn’t let your kids play with a 120VDC battery bank either. And safe voltage levels have nothing to do with the overall system complexity. You have a power source, distribution and consumers. Doesn’t matter if it’s AC or DC. Electrical systems get complex when you introduce multiple voltage levels, both AC and DC, different earthing systems, etc.

Cruise vessel for approx 400 people onboard.
Total power plant with 4 generators produces well over 10MW.
Main propulsion, which you won’t have is well over 6MW.
Chilled water plant for HVAC is about 700kW.
Refrigeration and freezer plant is about 250kW I think.
Galley about 500kW.
Hotel load for cabins also ranges in the 400 to 500kW if I remember correctly.
And if you care about the fire fighting system you can throw in another 400kW.

During normal operation you won’t use this amount of power, but redundancy, overhead, etc.
Hot water and steam is provided by diesel fired boilers.


This page shows several ways of doing it, including modifying an ac system to where the condenser/heat-exhanger uses cooler seawater instead of air. They also give numbers on energy savings.


Don’t be ridiculous. There is no easy way to create a simple and safe way for novices to experiment with AC in comparison to what novices can do with a 12VDC car battery.

Read what I wrote before you create strawman arguments to make a case against something nobody else has suggested.

There are portions of seasteading that don’t involve mega-ton ships and professional electrical engineering.

It is entirely legitimate for those homestead seasteaders to experiment with simple DC systems without needing the expertise of a ship’s electrician.