Basic Infrastructure

The necessities of life on a seastead: food, water, power, transportation, and so forth, present special challenges. Fortunately most of these challenges have been met in other contexts, and we can build upon those solutions. Thanks to the growing movement towards resource conservation, there are lots of commercial products which use resources efficiently and are thus well-suited for seastead life. Numerous books have been published on the topic of being self sufficient and living off the land. We used Building for Self Sufficiency by Robin Clarke [Clarke1976].

Seasteads can choose their level of self-sufficiency based on factors like size, distance to land, initial capital available, and desired levels of trade and luxury. The initial seasteads will probably be small and less self-sufficient. The variety of goods used in modern life is staggering, and it will simply not be feasible to make them all onboard. This is especially true because the ocean is a demanding environment, and it will be difficult to meet its challenges without some serious technology. Fortunately water transport is quite inexpensive, which makes importing many goods feasible. Thus we expect needs will be served by a continual series of compromises between local production and trade.

Different perspectives on self-sufficiency will yield very different choices. We've had libertarians and futurists scoff at the idea of growing their own food rather than just importing it, and we've had environmentalists who thought our ideas of self-sufficiency still depend way too much on the outside world. There is no "correct" solution, since the optimal seastead for someone who sees local, do-it-yourself production as a plus is different from the optimal seastead for someone who sees it as a minus. This may cause difficulties (and require compromises) on the first seastead or two, at which point the groups will probably split. Our exploration of these technologies is biased by our particular viewpoint on a good level of compromise, but keep in mind that more or less trade are always available options.

Similarly, there are a wide variety of lifestyles in the world. The right seastead for a billionaire will not be the right seastead for a simplicity-oriented group. It would be difficult for us to cover this entire range. Still, some technologies are better suited to the ocean than others, and the differences between groups will mostly be a matter of degree. Catching rainfall is a good way to get water - but different groups will use very different amounts of water. So reporting on methods is useful to everyone.

To get actual figures and guide our research, we had to use some target market. We tried to use the first-world environmentalist movement whenever possible. Environmentalists because they are efficiency-oriented, as we will be. First-world because frankly, its going to take that level of income to get the movement started. We think seasteading will be in reach of many Americans at the beginning, but not the third world. This does not mean that our movement will not help poorer people. We believe that a good way to bring cutting-edge technology to everyone is to start out selling it to the high-end markets, then let experience and economies of scale bring down the price.

There are two major differences that must be dealt with as self sufficiency books are applied to seastead technology. First, even though the seastead is surrounded by water, fresh water is going to have to be tightly managed. We do not have the option of tapping into a stream or drilling a well to get unlimited supplies of fresh water. Fresh water management is covered in greater detail in the water section below. Second, surface area will be at a premium. Large meandering structures that occupy lots of space are not going to be viable in early seasteads.

We should comment that most of these self-sufficiency books start out with a preface that we will paraphrase as "humanity is running out of energy and resources; thus, we must change our evil high technology ways and go back to basic living off the land." These statements should not be taken at face value, because many of them are not supported by scientific evidence. For example, books written in the late seventies, during the energy crisis, predict that energy costs would only get worse - when in fact they got (and have remained) much better.

More generally, the inflation adjusted cost of energy and resources have continually declined when measured over periods of greater than ten years. Contrary to the theory that increased population causes a decrease in material wealth, the twentieth century saw a dramatic and consistent increase in population along with a dramatic and consistent increase in material wealth. A more balanced view of energy and resources can be found in The True State of the Planet, a compendium of papers written by ten environmental scientists who publish in peer reviewed journals [Bailey1995]. A number of the energy books we reference below suffer from the same basic flaw, however, once you get past the preface and first chapter of these various books, they tend to be pretty reasonable.

An interesting counter-argument is that while people on land may have plenty of energy and resources, seasteads will not. The doomsday-type analysis which assumes limited and expensive resources is actually more applicable to our environment than the one it was written for. (To be fair, it is also somewhat applicable to remote pieces of land). So even those seasteaders who agree with our skepticism about apocalyptic claims should not dismiss such viewpoints completely, as they are relevant to this new frontier.

Water

{Patri - check whether PV/RO or distillation makes more water from a given amount of solar area.}

Despite being in the middle of an ocean, obtaining and retaining an adequate supply of fresh water is going to require some careful thought and implementation. There will be a continual loss of fresh water due to evaporation and other factors, so fresh water needs to be replenished. There are several possibilities for water replenishment -- rain water collection, distilling sea water into fresh water, reverse osmosis of sea water into fresh water, and importing fresh water. Of these, importing fresh water seems the least practical and rain water collection seems the most practical.

How Much Water Do We Need?

Water use on a seastead can be roughly divided into two major components: personal use and food production.

Water Requirements for Personal Use

The book Blueprint For Paradise by Russ Norgrove is (despite the title) an exceedingly realistic book about living on small islands. Norgrove suggests a water ration of 100-200 L/p/day (35K-70K L/p/yr) [Norgrove1983, p. 103-104], which we think is much too high. According to Neumeyer [Neumeyer1982], avg. household water use in the United States is 190 L/p/day (69K L/p/yr). A more recent source suggests use of 280 L/p/day (102K L/p/yr) in a typical single family home with no water-conserving fixtures [Water1999].

Fortunately, people on a seastead can easily use far less water than the average american [Economizing_on_Water_Use]. Folks living aboard their sailboats sure aren't using 150 liters of freshwater per person per day! Hill says:

People seem to use vastly differing amounts of water, some struggling on a gallon per day and others thriving on two pints. Pete and I manage quite succesfully on between five and seven gallons (19-26 L) per week between us, which amounts to a maximum of 4 pints (1.9L) per person per day. To achieve this, we don't seem to try very hard, but we do have water-saving methods, which make it easy and painless to be economical with our water use.
[Hill1993, p. 53]

As with most aspects of seasteading, there will be a trade-off between cost and convenience. As we'll see, obtaining the basic drinking requirements of 4 L/p/day will be trivial using any of our methods of water production. The quantities of water used on land (200-300 L/p/day) are feasible only in very rainy areas or at great expense. The individual preferences of seasteaders will determine what point in this range is selected. We'll use 5, 15, and 100 L/p/day as our points of analysis.

Water Requirements for Food Production

{ Better numbers would be nice. We have not found them. Empirical testing on baystead may be necessary. }

An analysis of a hydroponic gardening system as part of a proposed space station design suggests 720 L/p/day (although it also gives 30 L/p/day for personal use, which we feel is high) [Jewell2001]. However, this design has less need to be efficient because it is a closed loop (all water and biomass is recycled, so if they use too much water they still recover it).

Water usage for traditional crops is around 6-15 megaliters / hectare / year (rainwater and irrigation). This is 1.6 - 4.1 L/m²/day. Our crops will be much denser, increasing water requirements per unit area. However, they will also be grown hydroponically in greenhouses, decreasing water requirements per unit crop produced.

Non-greenhouse hydroponics: 2-4 L/m²/day[Bradley2001]. This should be an upper-bound on our water requirements, since greenhouses are more efficient. NIMSS reports an unpublished study in which 13.9 liters water were used per 1 kg of tomatoes in the field. In a greenhouse, only 2.4liters/kg were used. So the greenhouse is much more efficient, but since its denser, this doesn't tell us about water / unit area.

Theoretically, the only water losses from a food production system are evaporation, run-off and water contained in material which is removed (for consumption or composting). Run-off is eliminated in hydroponics, and water in material eaten goes to good use. Evapotranspiration is thus the dominating factor for efficiency. There are ways to reduce it [MBR, Ch. 29]. For example, using a greenhouse traps the water vapor in an enclosed space. Still, we must remember that "sweating" is an important method of cooling for plants. If the air becomes saturated with water, the plants will not be able to cool themselves, as well as being more vulnerable to fungal diseases. We could dehumidify the air without losing water by passing the air from the greenhouse through a condenser (perhaps using seawater for cooling), and capturing the resulting water. Essentially, this is treating a greenhouse like a solar still. We see a pretty good chance that this technique will be desirable.

Aquaculture will likely use saltwater species, and so won't contribute to fresh water requirements. Small animals, such as chickens, should have modest water requirements (drinking only), although whatever we feed them will have had water needs as well.

These numbers are very approximate, so we'll use a large range of 20, 85, and 500 L/p/day as water requirements for food production. This leads to total water usage checkpoints of 25, 100, and 600 L/p/day.

Economizing on Water Use

Water that does not get used does not need to be supplied. It should not be difficult for seasteaders to economize on water use:

• 28% of domestic water consumption is used for toilets [Water1999], which can be eliminated by using toilets which flush with salt water, or better yet, composting toilets which use no water and save the valuable nutrients.
• Seasteads will probably take their cue from the environmentalist movement and utilize multiple water systems, such as drinking water, grey water, black water, and so forth. An excellent discussion of designing net-positive-benefit greywater systems can be found at graywater.net
• Using greenhouses should greatly reduce our evaporative losses, by keeping moist air trapped inside the growing space.
• Hydroponics claims to require 1/25th as much water as conventional cultivation (this may include greenhouse gains).
• Residents can use misting showers.
• Water minimization technology for many common uses (dishwashers, washing machines) is widely available.
• As rain varies seasonally, water usage can vary as well, being used at high levels during the rainy season and low levels during the dry season. This effect can be created with quotas or with market-based systems such as adjusting the price of water.

How Much Water Can We Get?

"I mix my water myself. Two parts H, one part O. I don't trust anybody!" -- Steven Wright

Rain

Norgrove says that roof-based water collection is eminently practical - a reasonably large house roof, on most islands, will supply enough water for the residents [Norgrove1983, p. 103-104]. Assuming 30% loss of water, 1 m² of roof will yield 7 L/cm of rain. Average precipitation over the ocean is about 3mm/day, or 1.1m/year, with much less seasonal variation than on land (which is an advantage) [ERA40]. It is unclear from our source how much regional variation there is. So for every square meter of rain collection area, we get about 750 L/yr or 2.1 L/day:

Our current designs have about 30 - 50 m²/person. The highest checkpoint would represent a drastic decrease in our planned population density to achieve from rainfall alone. But if most of the top deck can collect rainwater, we can just about achieve the middle checkpoint without alternate methods. It is not hard to make the exterior of a greenhouse collect water, and much of the top deck will be covered with greenhouses. If the top deck is covered with a skin, this does the job easily as well. Or tarps could be raised during rain to collect water, and would serve the additional function of sheltering the top deck. Any rainwater collection device should let the first few minutes of catchment drain, to rinse off salt spray and small debris.

Areas that do not catch rainwater can be compensated for with water production or collection area elsewhere. We could build floating rainwater collection modules, since water collection apparatus (a big tarp) is light, cheap, and simple. This lets us cheaply use more area. One problem with this is that lightweight water collection (tarps) don't deal well with high winds, and rain often comes with winds. Also if they are low, they will catch some salt spray. We may be able to spread a tarp below the platform and above the waves to capture rain (as long as it falls at an angle), although it will catch spray as well. Tarps could also be projected out sideways from the decks, since they are very light.

If the seastead is parked in area that does not get regular rain storms, or it is the dry season, an alternative method of fresh water replenishment is needed. Either sea water distillation or reverse osmosis will work. Both methods require significant amounts of power, in the form of sunlight for distillation and electricity for reverse osmosis.

Solar Distillation

We can get water without rain using a solar still to purify seawater by evaporation. Solar stills have been used since at least the 16th century, and mass-produced since WWII, when 200,000 inflatable stills were made for the US Navy [ITDGStill]. Thus it is fair to say that they are a mature technology. Impure (salty) water is heated by the sun, and the water evaporates while the impurities do not. The vapor then condenses onto a surface which captures the water. Its a miniature version of the same cycle which produces rain. Solar stills are commercially available from [SolAqua] and [ADS]. They can also be built fairly easily with widely available plans [EPSEAStill]. Because the water has been distilled, it is purer than water filtered by reverse osmosis.

This method requires solar area, but since its very lightweight it can be projected out from the platform, or floated on separate units. As solar stills are closed, contamination by salt spray is not a worry. Lack of rain is usually associated with calm seas and clear skies, thus evaporation is an excellent complement to capturing rain.

Costs range from $60/m² [ITDGStill] to $120 / m² [EPSEAStill] unassembled, to $275 / m² for Agua del Sol's pre-assembled ADS-8. This is pretty expensive, but there is almost no maintenance cost and a still should last for 20 years. We also may be able to design larger stills and buy components in bulk to reduce the price. Ferrocement is a good material for stills, thus we could incorporate them directly into the top deck. These stills produce 2.65 - 7.6 L / m² / day, depending on the amount of sunlight according to EPSEA [EPSEAStill] which is located near the US/Mexican border , or an average of 2.27 L m²/day in a typical country according to ITDG [ITDGStill].

Solar Still footprint and cost per capita:

These figures indicate the cost of meeting all water needs with solar stills. Any rainfall collected will reduce them. Also, we suspect we can achieve lower costs than our references ($7.5 - $35 / L / day). Stills will be most useful in areas with high sun and low rain. The current range of costs is wide, and represents very different levels of cost-effectiveness, thus further research and experimentation with actually building stills is needed. Note that stills are fairly thin, so they can be stored in stacks, and deployed on the top deck during droughts or dry season. Because of their design, stills can also double as rainwater collection area.

Recent research suggestions that a clever design improvement can greatly increase the efficiency of a solar still [Goswami2003]. The idea is to use gravity to create a partial vacuum through hydrostatic pressure, which increases the rate of evaporation. Tests on a small prototype resulted in almost twice the efficiency of flat basin stills. While the method is more complicated, it is not tremendously so, and is definitely worth investigating further for cost-effectiveness [Hoover2003].

Several companies also make floating solar stills, which are inflatable, plastic, and cone-shaped [LandfallStill], [AquaCone]. This could allow a seastead to use extra solar area, which would be a major advantage. While individual units are quite expensive ($300-$1000 / m²), we should be able to reduce cost by buying in bulk, constructing larger units, and/or producing them ourselves. Space on the ocean's surface is cheap, but space on our top deck is expensive. Solar stills don't really need to be held safely above the waves by our concrete pillar (except during storms), so deploying them is great if we can manage it.

Multi-Stage Solar Flash Distillation

In flash distillation, the brackish water is not only heated, but exposed to a vacuum to reduce it's boiling point. This causes flash evaporation, leaving a residue of salt. Multiple stages can achieve reasonable freshness. This method is much more efficient than simple solar distillation - the energy required to create the vacuum has more of an effect than if it were used to simply heat the source-water further. As a result, it is used in more than 2,000 desalinization plants worldwide.

Like solar distillation, this method requires a large amount of space to heat the brackish input water, which is a definite disadvantage for a seastead. However if some form of distillation is going to be used, its probably best to use a vacuum (perhaps just through hydrostatic pressure).

Reverse Osmosis

Reverse osmosis uses a semi-permeable membrane as a filter, which can pass water molecules but not contaminants such as salt molecules. It requires continuous pressure, usually from a pump, to operate. One reason R/O is considered undesirable in some environments is that it uses 4-5 times as much water as it produces (the remainder is waste), but since seawater is, shall we say, rather plentiful where we'll be, this is not an issue. One nice feature of R/O is that it uses little space, and the cost is basically constant for a medium-sized system or bigger, so it is cost-effective on our scale.

Seawater R/O systems are more expensive than freshwater, for example the APEC 600 gallon / day (2300 L) system costs $7500 ($3.30/L/day of installed capacity). There are some maintenance costs for filters. The Army Corps of Engineers estimates that in Florida, R/O on seawater has a capital cost of $1.34 - $2.38 / L / day and operation/maintenance costs of $0.01 - $0.015 / L [UNEP1997, Sec. 2.1 Table 5]. Anecdotal reports suggest that R/O machines are not completely reliable, and will require occasional work [Norgrove1983, pp. 117-118]. .

The main cost of R/O is the electricity used to power the system. According to the specs for the APEC and for Filtration Systems Dolphin series (800 - 1600 GPD), R/O produces approximately 50-100 L / KWhr of energy.

(Power system costs were estimated using PV panels. Wind turbines will probably be cheaper, but we don't have good numbers). Clearly electricity costs are the dominating factor. R/O costs including electricity are actually pretty similar to a pre-constructed solar still, but much higher than building stills ourselves. However R/O has a significant advantage: installed electricity generating capacity can be used for other things when not needed for R/O. Thus R/O is more flexible than distillation. If the seastead's energy needs or production are erratic, excess capacity can be used to power an R/O system to fill the cistern.

If greywater is available, feeding that to R/O increases efficiency, as reader Doug Jones points out. This is because the unit can operate at lower pressure due to the lower salinity (ie water is closer to pure already). This uses less electricity.

Since we plan for a generating capacity of about 1.4 - 4.1 KWhrs / p / day [Power], production of water by R/O is clearly feasible, energy-wise. Because installed R/O desalinization capacity is cheap, a good approach might be to install a fair amount of it, then run the R/O plant when there is surplus energy or low water supplies.

Water reuse

We can reduce our need to generate fresh water by using what we have multiple times. While drinking requires a fairly pure source, many other applications can use lower grades of water. For example, "grey water" (water used in the home for non-sewage purposes, including dishes, showers, and laundry) can be used for gardening or toilet flushing. With some processing, grey water can be re-used for other non-potable applications. There is a lot of literature from the environmental movement on this subject.

Importation

As with other resources, the feasibility of water importation depends on how far the seastead is from civilization. A coastal seastead could outfit or construct a water-tank barge. The cheapness and ease of rainwater collection, however, makes this an unlikely option. Still, certain configurations of circumstances (little local rainfall, high water use, close to shore) could make it worthwhile.

Other Considerations

Norgrove's major concern was cistern size for riding out droughts - 3 month droughts in the tropics are to be expected, and he says you should have at least 20 m³/person of cistern capacity to deal with this [Norgrove1983, p. 104-109]. In our case, 3 months supply would be 2,250/9,000/54,000 L/person. However, rainfall is less variable in the ocean [Era40], and we can always shift more of our electricity towards R/O, so this much storage is rather excessive for ouur purposes.

One intriguing possibility is to float a bag of freshwater in the ocean as a cheap, large cistern. This would save space and weight on the main structure. However, water actually doesn't take up that much volume. Also, since water can be produced steadily, large reserves imply that too many resources have been spent on water production. Still, for regions with monsoon/drought patterns, or seasteads which experience such patterns due to their migration path, it might be a useful technique.

A concern that must be dealt with is salt water contamination. As waves crash in the ocean around the seastead, small droplets of ocean water are formed that are blown around by the wind. These small droplets can land on exposed soil and slowly increase the soil salinity. Once the soil becomes too salty, crops will no longer grow. One solution is to do all crop growing in covered greenhouses on the seastead, which has other advantages (reduces evaporation, provides a surface for capturing rainwater). If we use a hydroponic system, there is no soil, and it is normal to change the nutrient water and flush the substrate periodically.

Some chemical treatment (such as chlorine) may be desirable in order to prevent contamination during storage and distribution of potable water. Fortunately, because we are starting with clean water, much lower doses are necessary than with chemical purification. In fact, one nice thing about most of these methods is that they result in clean, drinkable water without the use of heavy-duty chemical treatment.

Conclusion

As you can see, there are several ways we can produce water, and combining them will result in the most robust system. Capturing/producing enough water for drinking and hygiene will be quite easy, except in particularly dry locations. Depending on crop requirements, we may have to go to some extra effort to generate or reclaim water for farming using one of the many methods listed. Large-scale traditional gardening will not be feasible.

Food

When it comes to food it is necessary to decide how self-sufficient the seastead should be. There is a spectrum of choices available from importing everything to producing everything locally. Realistically, seasteads are unlikely to be 100% self-sufficient due to lack of available space, capital, and the fact that people can only stand to eat so much algae. A reasonable goal for an early seastead is to grow its own fruits and vegetables and get some of its protein from aquaculture.

Importation

In ancient times, with transport crude, slow, and pricey, most trade involved goods with a high ratio of value to mass...But over the centuries, as transportation grew more cheap and routine, trade in bulky essentials grew practical. Even in the Roman Empire, hauling wheat long distances over water had made economic sense.
[Wright2000]

Shipping food is clearly feasible, given how commonplace it is in the modern world. Staples like rice, wheat, and olive oil require a lot of growing area. Yet they are dense, inexpensive to purchase, and easily stored, which makes them ideal to import. So trade is always an option - and will be a necessity if a varied diet is desired on early seasteads. A small community simply cannot produce a large variety of items, so it will be a long time (if ever) before local seastead produce can rival the set of choices available in modern supermarkets. While residents will naturally cut back on imported foods, they'll still want something different on occasion. (This has been true throughout human history). This will be less of an issue on tourism-based seasteads with a mainly transient population.

Another way to look at importing food is to consider the economic idea of comparative advantage, explained by David Ricardo in 1817. He demonstrated that nations prosper most by doing what they are relatively best at. Solar area on a seastead is expensive (we have to build our own land), and agriculture is an industry with a very low income per unit area. So, much like terrestrial cities, seasteads should focus on industries which are not space-intensive. Breakwaters may eventually render new land cheap enough for agriculture, but early spar seasteads are not going to find it cost-effective. There is nothing unique about importing food, so we won't go into detail.

Growing Plants

There is a long history of people supplementing their diet with home grown vegetables. During World War II, these gardens were called `Victory Gardens' and the name has stuck ever since. An excellent guide to home gardening is Square Foot Gardening by Mel Bartholomew [Bartholomew1981] (also made into a popular PBS series). This book is notable in that it tries to minimize the amount of time spent in the garden. Most other books seem to focus on gardening as a hobby and tend to soak up as much time as they can get. The goal of square foot gardening is to spend just a few minutes a day on garden maintenance. Its methods claim to produce enough fruits & vegetables for a person in only 4 m².

One real advantage that the seastead has when it comes to growing crops is that it is possible to reduce or eliminate weeds and insect pests. This is extremely difficult to do on land, since the weeds and pests are just blown across the property boundary. With a seastead, which is naturally isolated from terrestrial ecologies, care can be taken to minimize the number of insects and weeds that take hold on the seastead.

While some items (fruit or nut trees) may be grown in dirt outside, we expect the majority of farming be done hydroponically in greenhouses. We present some data on how much area per person is required, but unfortunately our numbers are a bit rough. Also, they will depend strongly on the level of self-sufficiency and type of diet desired.

{ Talk about which plants? It matters a little, but enough? }

Greenhouses

We expect seasteads to use greenhouses heavily, since they offer:

• Insulation that keeps the frost out and the warmth in. This allows year-round gardening, and thus more harvests per year.
• Protection from harmful UV radiation (if the correct materials are used).
• An enclosed airspace, which allows the operator to control humidity by venting humid air. This helps prevent fungal infections.
• A barrier against pests.
• Less water use (even with occasional air venting).
• Protection from salty spray.
• Outer skin which can easily be used to collect rainwater.

Hydroponics

Hydroponics is a farming method in which plants are rooted in a liquid nutrient solution, rather than soil. This high-capital, high-yield industry has grown 4-5 fold in the past decade. Hydroponics has a number of advantages over conventional field farming:

• Gasses dissolve more easily in water than soil, so the plants are better aerated.
• Nutrients dissolve better in water also, so the roots can be in a more nutrient rich environment.
• As a result, the plant has smaller, more efficient root systems and can devote more of its energy towards growing the parts we want.
• With smaller roots and a more resource-dense environment, plants can be spaced much more closely, which greatly increases yield per unit area.
• Unused water is reclaimed, rather than draining off into the soil as in conventional gardening. The result is much higher water efficiency.
• Labor associated with soil management (ploughing, turning, etc.) is eliminated.
• Clever methods can further increase yield. For example, using multiple beds, stacked vertically, which continually rotate on a frame so that all the plants get sunlight. One manufacturer claims a 3-17 fold increases over traditional hydroponics yields [AB_Hydro].

The main concern of a seastead is yield per unit area, and many of the advantages of greenhouses and hydroponics are multiplicative on this quantity. For example, twice as many crops per year and twice as dense crop spacing would together mean a four-fold increase in yield. In practice, a factor of 5-10 times is common [Roselle1996], [Willis1992, Ch. 2]. Yields as much as 100 times higher have been achieved [Willis1992, Ch. 2].

It is reasonable to wonder whether these numbers are too good to be true. Keep in mind that we are just talking about crops per unit of area. Hydroponics does use other resources, like nutrients and water, more efficiently than conventional gardening, but this factor is much less than the yield/area factor we're focusing on. For example, more crops per year means a better yield, but also more picking time, fertilizer used, etc. Another downside is that the capital costs of hydroponics can be quite high. Since farmland is relatively cheap, hydroponics are usually not worthwhile, even with the advantages listed above. On a seastead, however, solar area will be at a premium, and so a technique which minimizes area use is just what we need.

The figures we found for hydroponics equipment cost varied hugely, from $5/m² for simplified home systems in the third world [Bradley2000] to $150/m² for commercial first-world operations [AmericanHydroponics, sample costs]. There's a good chance seasteads will be towards the expensive end of this range in order to maximize yield, but experimentation and DIY could bring costs back down. Empirical data gives yields for many hydroponically grown vegetables are of 50-250 g/m²/day.

It is important to be careful of water-borne diseases, since many plants share the same nutrient solution. For this reason, in most indoor operations, the growing medium is sterilized between crops [Willis1992, Ch. 2].

Genemod Saltwater Plants

Gardening, even with hydroponics, will use considerable fresh water. Recently, scientists have produced genetically modified tomatoes which can be grown in saltwater. The plants extract salt from the water and store it in their leaves (which offers intriguing possibilities for reclaiming salinated land). The most exciting part is that the plants are made saltwater tolerant by the introduction of a single gene which codes for a protein for dealing with salt. This means mean that many plants could theoretically be modified in the same way. However, the plants are not able to deal with pure seawater. Also, we won't be able to compost the salty leaves. So we save freshwater, but lose some organic material [Zandonella2001].

Note that GMO plants are unlikely to take over the ocean, since they can't deal with pure saltwater and they need to be immersed in a nutrient-rich medium. In general, they are not adapted for the ocean, which makes them far less likely to spread than GMO's on land.

Seaweed

No seastead diet would be complete without the one "plant" evolved for the ocean environment. Seaweeds are actually a form of algae, and people have been eating them for thousands of years, particularly in the Orient. None are known to be poisonous, although some can cause discomfort. Extracts such as agar and carrageenan are derived from sea plants and used in a large variety of packaged foods. Seaweeds are rich in vitamins, minerals, and protein, and can be used to fertilize other plants. Ironically, the vitamin C in seaweed might have saved early seafarers from scurvy, if only they'd known to scoop it up! [Neumeyer1982, Chapter 6].

Seaweed can be cultivated by placing fragments on ropes or other substrata and growing them in the ocean.

Spirulina Algae

Spirulina has the most remarkable concentration of functional nutrients ever known in any food, plant, grain, or herb. On top of this, spirulina delivers more nutrition per acre than any other fod on the planet. This has extraordinary implications for more efficient and less damaging food production for the future. Every day new research brings to light the wonders (hidden) in microscopic algae.
[Spirulina1994, p. 5-6]

While books like Earth Food Spirulina can sound a bit over-the-top at times, author Robert Henrikson knows the subject well - he's the president of Earthrise Farms, the largest spirulina farm in the world . Blue-green Spirulina algae, used as food by the Aztecs , is 65% protein by weight, and is a complete protein source. Because it is such a simple life-form, it is much easier to grow and harvest than crops or livestock. Algae waste no growth on inedible parts, and every cell is a seed. Their life-cycle is simple, and they grow at an exponential rate until nutrients are exhausted (doubling biomass every 2-5 days). Spirulina can grow in sea water, and be eaten without any processing. It contains vitamins as well, including A, E, and B12 [Spirulina1994].

It has been suggested that spirulina provides more nutrition per acre than any other food - and without requiring fertile soil or fresh water. Current production costs in large facilities range from $10-$20 / kilo. Compared to the extravagant conventional methods of obtaining protein from mammals, spirulina provides an incredibly efficient one-step food chain, as can be seen in the table below.

Another advantage of spirulina is that it produces oxygen as a positive externality. Unlike some algae, it is not nitrogen-fixing, and so requires a supply of nitrogen (perhaps from an artificial upwelling, such as a wave pump). One intriguing use for spirulina is to concentrate nutrients from seawater so that they can be used to feed more complex life forms. While spirulina thrives in salty and alkaline water, most strains don't grow well in seawater, which has low carbonate and high magnesium and calcium. But special seawater strains are being developed.

Mycoprotein

Fungi are another lower life-form which can be used as a food supply. Protein derived from them is called mycoprotein, and produced by continuous fermentation. It has the advantage of being "chewy", as well as absorbing added flavors and colors. Unfortunately, as reported by the CSPI, there have been many negative health reports about the commercially available mycoprotein [CSPIQuorn]. Medical investigation suggests that individuals with mold allergies may be allergic to mycoprotein as well [Hoff2003]. This problem seems to occur only in a minority of the population, but we advise caution, since serious allergic reactions can be fatal. Still, this is another potential way to grow protein.

Resource Inputs

Resources necessary for food production include water, light, fertilizer, labor, and space. Light is provided by the sun, water by the methods outlined earlier, labor by the residents, and space by the seastead. Fertilizer is a more complicated issue, as this excerpt from an article on space station biosystems demonstrates:

Previous work on hydroponic systems have shown that nitrogen balance cannot be achieved, especially with systems that involve organic matter (Jewell et al. 1993). Some nitrogen "leaks" from hydroponic systems, most likely as a result of micro anoxic environments where conditions for microbial denitrification are favorable. These conditions include zero dissolved oxygen and the presence of biodegradable organic matter. When these conditions occur many bacteria have the capability to use electrons from oxidized forms of nitrogen [ NO₃- (nitrates) and NO₂- (nitrites)] and reduce these valuable plant fertilizers into unavailable nitrogen gas. In sewage treatment hydroponics, between 25 and 50% of nitrogen has been observed to be unaccountably, presumably because of denitrification.

Hydroponic systems that maintain water free of biodegradable organics, high oxygen levels, and low oxidized nitrogen concentrations will discourage loss of nitrogen via denitrification. A conservative design would assume that as much as a quarter of the cycling nitrogen will be converted to nitrogen gas (N₂ ), or a total mass of 15 g of nitrogen must be transformed from N₂ to organic nitrogen each day in a closed biosystem.

A sustainable system must replace this nitrogen fertilizer loss via nitrogen fixation. Two biological options are available to convert N₂ to organic nitrogen which can be subsequently biologically regenerated as ammonia-nitrogen or nitrate-nitrogen: symbiotic N₂ fixation in legumes and N₂ fixation in blue-green algae. An option that could be used to generate useful biomass with minimal side affects would include symbiotic N₂ fixation using legumes, possibly food producing legumes such as soybeans.

Unfortunately, nitrogen fixation is a highly energy intensive process, and rates are relatively slow. Depending on the length of growing season, documented fixation rates vary from 0.008 to 0.18 g N/m² -d. Growing areas to make up a 25% loss would be 83 m 2 to 1,900 m² . This nitrogen management plant area could be equal in size to hydroponic food production. It will be assumed that no human food results from the nitrogen fixing hydroponics.

A summary overview of the closed biosystem for one adult is shown in Figure 5. Total plant growth area is 290 m².
[Jessell2001, pp 9-10]

Fortunately, we don't need to manage our nitrogen balance quite as carefully as a space station. For instance, we can purchase nitrates produced on land using the Haber-Bosch process. Those seasteads which seek completely sustainable farming, however, must keep this problem in mind. Composting and similar closed-cycle techniques can reduce the amount of new fertilizer needed. Composting is covered in both Building for Self-Sufficiency and Square Foot Gardening. There may eventually be clever methods of extracting fertilizer from the ocean (artificial upwelling, concentrating nutrients with algae, etc.). But until then, even with these techniques, some fertilizer will need to be imported.

Artificially lighting a greenhouse to produce a longer growing day takes about 50 - 175 W / m² of power [MBR, Ch. 5], [Andrew1994]. At 20m²/person, this would be 1 - 3.5 kW / hr. So 12 hrs/day, 365 days/year of lighting would use 4-15 mWhrs/person/year, which is significantly more energy than is required for personal use. Since power onboard a seastead is expected to be expensive, this will probably not be worthwhile. For example, using photovoltaic panels for this purpose would be absurd, since they'd take up around 10x as much space as the plants they were providing electricity to light! Still, it is possible that special factors (excess power, cheaper power generation, trade embargo) could change this.

There are some other ways we might increase grow area. Mirrors or other sunlight collection devices could be used to gather sun from a larger area than the platform, lighting a second deck. Another possible solution would be to make small rafts or barges as auxiliary grow areas. They would be constructed cheaply, only able to withstand typical non-storm seas, and deployed around the stead. They would be sized so that in foul weather they could be hoisted up under the stead for protection. Fresh water could be piped to the units, or integrated solar distillers used.

Raising Animals

There are several ways we may be able to supplement the production of our gardens, such as fishing, aquaculture, and raising farm animals.

Fishing

Fishing is heavily regulated inside EEZ's, so it may be problematic. Also, a seastead can't just zoom around looking for fish like boats do. However, seasteads may find fishing economical if they are in locations where the stock has not been depleted by commercial farmers. This could even make for a profitable seastead business [Market-Fishing Base].

Aquaculture

Aquaculture, the process of raising ocean foodstuffs, is the maritime equivalent of ranching. This practice has a long history: Chinese manuscripts indicate that fish culture has been practiced there since at least the 5th century BC, and the Romans raised oysters. The list of animals that have been raised commercially starts with Abalone, Amberjack, Anchovy, and continues on for another 100 species [WorldAquaculture].

Unlike the commercial fishing industry, which is slowly succumbing to the exhaustion of its commons, aquaculture systems offer long-term promise. This is true whether you look at it from the environmentalist's perspective of increased sustainability, or the economist's viewpoint of more clearly defined property rights. Given the incredible impact of the agricultural revolution, we can't help but speculate that the movement from hunting wild fish to farming domesticated ones will also produce major gains in efficiency and worldwide food production.

Saltwater plants dovetail nicely with aquaculture because the waste products of fish can be used to fertilize plants. This system is called Aquaponics. For example, on Carl Hodges' experimental farm, shrimp grow in saltwater, then tilapia, and then the water is used to nourish a saltwater plant called Saliconia (used for vegetable oil) [Hinman1996]. {CENG: prev par unclosed}

Aquaculture is roughly divided into intensive and extensive. Intensive is more complex, as it involves creating an artificial environment in which to raise the product. Extensive can be as simple as "fencing" off a section of ocean with nets, and raising some fish inside it. By choosing species which feed on the natural detritus of the ocean such as algae, no food supply is needed. While this tends to be a low-density, slow-growth method, its also low-effort and uses renewable resources. N55's SMALL FISHFARM is an example of a simple design [N55BOOK, pp. 167-176].

Farm Animals

Raising a small number of dairy animals will probably be worthwhile, such as chickens (for eggs) and cows (for milk). Chickens run about 8 to the square meter [SpaceSettlements, Ch. 5], although growing their feed will use area as well. Chickens, cattle, rabbits, and similar animals can be grown for meat, producing edible portions of about 1/5th to 1/10th of the mass they consume [SpaceSettlements, App. C]. Unless a cheap food source like algae can be fed to animals, importation is probably a better way to get meat.

Area Requirements

{ more numbers would be great here, if anyone has them }

Numbers in the literature on the area required for self-sufficient food production vary widely. This is not surprising, since the environments discussed are very different. Meat takes much more space than vegetables and starches, and a complete diet takes much more space than supplementary fruit, vegetables, and dairy. Conventional, open-field agriculture uses a lot more room than hydroponics on a space station.

We think the latter is more relevant to us than the former. Common sense tells us that when a resource is scarce, people find ways to use less of it. Farmland is much cheaper than seastead deck space, so we will use the latter more efficiently. We'll have to use more of other resources to do this of course - if there was a way to use less space with no cost, it would already by part of standard practice. But while we aren't getting something for nothing, we can be pretty sure that our yield per unit area will be higher than on land. One advantage we have compared to space stations is that we can draw from the resources of the ocean, including fish, seaweed, and nutrients, as well as importing from the outside world.

A representative land-based figure is the Biosphere II project, which attempted to be a completely closed ecosystem. They grew 80% of their food on 253 m²/person, which would mean 316 m²/person for self-sufficiency.

Food requirements are about 3.1kg [Shipman1989], and 2000-3000 cal per person per day. A NASA project on space station design says that about 15-50 m² of solar area are necessary to provide a standard North American diet with high-yield techniques [SpaceSettlements, Ch. 3 and App. C]. This includes cattle and chicken raised for meat, which are area-intensive. On the other hand some of their numbers strike us as a bit optimistic. A different space station study suggests that all area required for complete self-sufficiency, including waste / water recycling, food self-sufficiency, and nitrogen balance, is 290 m²/p [Jewell2001].

Sailing the Farm, a book about self-sufficient boating, implied that using a cabin for food production (5-10 m²) could make a substantial contribution to the sailor's diet. As mentioned earlier, Square Foot Gardening states that only 4 m² / p are necessary for fresh vegetables.

Based on these figures, complete self-sufficiency would require about 50-300 m² / p, which is not practical at current cost estimates. However, a substantial amount of food (vegetables, fruit, dairy) can be grown in only 5-20 m² / p. Fishing, aquaculture and dense imported foods (grain, cheese, meat) will round out the seastead diet. Vegetarian tendencies and a willingness to eat unusual things like algae will shift seasteads farther towards self-sufficiency.

Power

{ Efficient refrigerators and freezers are available, and if they are heavily insulated, refrigeration can be maintained by running the cooler for an hour a day, about a 4% duty cycle [Norgrove1983, pp. 126-127]. }

Our seastead is going to need power, both for personal use and to support its infrastructure (food production, water purification, transportation). OTEC no good.

There are other workable alternatives that are both less capital intensive and more technologically mature, such as solar power, wind power, and wave power. (Nuclear power is yet another alternative, but it is extremely capital intensive and politically difficult; in terms of seasteading, nuclear power makes OTEC technology look easy.) Basically all of the alternative power sources have one problem in common -- the power is intermittent. Solar power does not work at night, wind power does not work when the winds are calm, and wave power does not work when the seas are calm. The best solution to this problem is twofold: collect and store excess energy for times when power generation is not available, and use multiple energy scavenging technologies to smooth out the availability curve.

Energy Storage

For now, the most mature technology for storing energy appears to be electrochemical batteries. While they are expensive, the alternatives (flywheels, ultracapacitors, redox batteries, creating hydrogen to power fuel cells) are generally still experimental. However, redox batteries are rapidly approaching usefulness.

Electrochemical Batteries

Batteries are one of the most expensive parts of an electrical system. They don't store much energy per unit weight, and they don't last through many charge cycles:

"Batteries have always been an expensive and troublesome part of off-the-grid systems. Consider that a typical 6-volt storage battery has a gross capacity of 200 Amp-hours, equivalent to about 1 kWh of chemical energy, and costs nearly $100. Thus, batteries cost about $100/kWhr of gross capacity, not counting shipping costs. And shipping heavy batteries is costly. Moreover, not much more than 50 percent of the energy stored in a battery can be withdrawn without sulfating the plates and reducing its effectiveness. Batteries also have a limited lifetime. The Folkecenter for Renewable Energy estimates that batteries are good for about 2,000 cycles. (Batteries are still useable after 2,000 cycles, but they have reduced capacity.) If a battery discharges 50 percent of its gross capacity through 2,000 cycles, it will deliver about 1,000 kWh of net electrical energy over its operating lifetime. Thus battery storage alone costs more than $0.10 per net kWh of useable energy in an off-the-grid system." [Gipe1999]

Ten cents / kWhr is around what power from the grid costs - and this is for battery storage alone! Because of this, we want to match up power supply with demand so that we need to store as little energy as possible. It will help to have needs with flexible timing, such as refrigeration or running reverse osmosis systems. These can be run whenever we're generating excess power. When other storage technologies become more reliable, they should be investigated. While batteries have their disadvantages, they are mature and robust and their cost is high but not prohibitive.

Vanadium Redox Batteries

The current forerunner to replace conventional batteries is the Vanadium Redox Battery developed by Professor Maria Skyllas-Kazacos and her team at the University of New South Wales, Australia [UNSW-VRB]. A redox battery consists of two chemical solutions which produce an electric potential when combined. When originally developed, they had the problem that the used combination of chemicals was toxic, caustic, and useless. The solution was to use a proton exchange membrane, like a fuel cell, to utilize the electrical potential without allowing the fluids to mix. Unfortunately, even with these membranes, some cross-contamination occurs.

The UNSW researches came up with a clever solution: using the same chemical for both halves of the cell, but in different electric states. Now cross-contamination just causes energy loss, not damage to the solution. Vanadium dissolved in sulfuric acid was the answer, although it took some effort to create a solution with a high enough concentration of vanadium to get a decent energy density. The advantages over conventional batteries include:

• Storage capacity limited only by tank size and amount of vanadium solution. So you can increase capacity just by getting more tanks and fluid.
• Number of charge/recharge cycles is theoretically infinite. In practice at least 16,000 (much higher than batteries).
• Energy storage and extraction are separate, so the capacity of either can be increased without affecting the other.
• Shelf life is indefinite, and energy does not leak during storage (unlike batteries, flywheels, capacitors...)
• High efficiency (80%-90%) because redox couples are electrochemically reversible.
• Fast charging, can be fully discharged with no adverse effects.
• Can be recharged by transferring fluid, as with gasoline engines, except the fluid is rechargeable. So, for example, if the seastead and its boats both used this technology, the boats could be refueled by pumping in new fluid, instead of slowly charging conventional batteries.

VRB has been used in actual, large-scale applications since about 1997 - its not just theoretical. This includes a 450 kW / 1MWhr VRB system at the Kansai Electric Power Plant in Japan and a 25 Kw system used to store power from the wind power generator of Hokkaido Electric Power Co. It seems quite likely that the home power market will adopt VRB's when they become commercially available. The fuel cell will cost about $200-$500 per kilowatt and the electrolyte about $40-$60 per kilowatt-hour. The fuel cell membrane will last around 8-10 years, and the electrolyte can be re-used indefinitely [Skyllas2004].

Hydrides

As described elsewhere, a seastead may wish to store hydrogen for use in cooking. Unfortunately, hydrogen in gas or liquid form is difficult to store. The liquid must be cooled to -423 degrees, and the gas must be compressed to very high pressures or you don't get much energy density. Being a small element, hydrogen is hard to contain. An interesting alternative is to store hydrogen energy in solid or liquid hydrides, which release hydrogen gas when combined with water.

Since water is rather common, solids such as sodium hydride are quite dangerous in their natural form. Hence the invention of Powerballs - small pellets that are coated in plastic. The plastic is waterproof, so the hydride won't react accidentally. But simply cutting a ball when it is immersed in water produces large amounts of hydrogen. The energy density is about 6 times higher than compressed hydrogen gas at 3000 psi. The reaction's waste product is sodium hydroxide (NaOH). New powerballs can be created simply by heating the NaOH to create NaH, pelletizing it, and coating it in plastic [Powerball].

Another option is a liquid hydride such as sodium borohydride (NaBH4). Since it only produces hydrogen in the presence of a catalyst, it is even safer and less likely to produce a runaway reaction. The reaction product, as with sodium hydride, can be used to re-generate the fuel. Millenium Cell is producing these systems and they are starting to be adopted in fuel-cell powered concept cars such as the PSA Peugeot Citroen and the Chrysler Town & Country Natrium [MilleniumCell].

The main issue for seasteaders is what facilities are necessary to re-generate these fuels. If large manufacturing plants are needed to create hydrides cost-effectively, they aren't good methods of energy storage. But if we can get a reasonably priced black box that takes energy and spent fuel and creates charged fuel, these might be good ways to store hydrogen. The technology is still a little too cutting edge for early seasteads.

Flywheels

Flywheels have gotten to the point where a few commercial models are available. However, they really don't store very much power compared to batteries, nowhere near enough to function as the reserve for a renewable energy system. Also, the seastead is a constantly moving environment (albeit a slow one), and unless the flywheel is on a very expensive mounting system, this movement will drain the stored rotational energy. Finally, since the seastead is not rigidly connected to the earth, spinning up a single flywheel would make us spin in the opposite direction! This could be fixed by using two flywheels with opposite spins, but it makes for an amusing mental image.

Supercapacitors

The new generation of supercapacitors feature significantly higher performance, and are moving rapidly towards being useful for power systems. Michio Okamura and JEOL have developed these nanogate-based supercapacitors, which have much higher current densities and lower leakage than traditional caps. They are used in a hybrid truck by Nissan Diesel Motor and a fuel-cell passenger car from Honda, both introduced in 2002. Capacitors have the advantage of unlimited charge/discharge cycles within their ~10-year lifetime. They can also discharge very rapidly (hence their use in automobiles).

However, capacitors cannot yet replace batteries because they don't store very much energy - only 1-10 Wh/kg (compare to lead-acid batteries 30 and NiCads 50). Also they leak over long periods of time. Currently they are best used in power systems to smooth out loads by acting as an energy buffer. Batteries keep them charged, and the caps handle energy spikes. While maintaining them takes extra energy, remember that the big problem with batteries is the limited number of charge/discharge cycles. This technique reduces the amount of cycling and can greatly increase battery lifetime [JETRO-Cap].

Gravity Battery

There is another energy storage system that has a slim chance of being useful. That is pumping sea water up to a tank on top during the day, and running it down to the ocean during the night. Power companies use such systems to even the load on the power grid. (They pump water uphill during the night they run when power demand is low, and run it down during the afternoon when power demand is high.) However, we have serious doubts about the viability of this system for a seastead for several reasons. One is that it will make the structure more topheavy, which is bad for stability.

Hydrogen

While hydrogen has its advantages for cooking, storing large amounts of it is impractical. It requires either a lot of storage space, or high pressure systems which are quite expensive.

How much do we need?

To calculate energy costs and design a seastead, we need an estimate of how much power we are going to use. As with other resources, we expect to be much thriftier than on land, so there is some guesswork involved in estimating the numbers. According to the California Energy Commission the average household in california uses 6.5MWHrs/year [CEC_Solar]. A typical California Bay Area household uses 3.6 - 5.5 MWhrs/year [Yarris1994]. Chris Marnay's solar-powered house, which uses energy-efficient technology such as flourescent lighting, uses 2-3 KWhrs/day for 2 people, which is 0.5 MWhrs/p/yr [Yarris1994]. Other solar-powered homes use 1-2 MWhrs/p/ yr.

There are many ways to economize on a seastead. Appliances will be energy efficient. The large concrete bulk of many seastead designs will act as insulation and a heat sink, moderating temperatures (which tend to be moderate on the ocean anyway). Water can be heated by the sun, and air conditioning can be done by pumping cold seawater up. Based on this, and the numbers above, we estimate energy usage on a seastead to be in the range of 0.5 - 2 MWHrs / p / year. This is 1.4 to 5.5 KWhrs / p / day.

How much can we make?

There are a number of energy generation technologies, and creative minds can come up with many more fascinating and speculative ideas. The authors certainly have a few they'd like to experiment with. However, as usual, for initial seasteads we want to stick with mature options, which limits the possibilities.

Solar Power

There are an endless variety of ways to use solar energy - photovoltaic, solar heating, solar dynamic, etc. For electricity, we will focus on photovoltaic power, as it is the most mature. We'll also briefly discuss some other ways to use sunlight.

Photovoltaic Power

Photovoltaic (i.e. solar cells) technology was originally developed to supply power to satellites in outer space, a remote and hostile environment. It transforms sunlight directly into electricity. Currently, photovoltaic power can make economic sense for remote areas that do not have a connection to the electric power grid (like seasteading.) There is now a large body of practical experience with photovoltaic power that we can apply. The reference we used was The New Solar Electric Home by Joel Davidson [Davidson1987]; there are many other appropriate alternative books on the subject.

Photovoltaics have a number of disadvantages:

Cost

Photovoltaic panels are expensive. They keep coming down in price, but they are still not cheap.

Efficiency

Even the most efficient photovoltaic cells have only recently started to achieve conversion efficiencies over 30% and these are horrendously expensive. The commercially available solar panels have conversion efficiencies in the 8-15% range. This relatively low energy conversion efficiency means you need more solar panels covering more area to achieve the desired level of power generation.

Battery Storage Required

Since the sun does not shine at night, there is no power coming in from the solar panels then. So it is necessary to collect additional energy during the day and store it for night time use. The most sorage method is to use a bank of batteries. The batteries are expensive and this increases costs.

Solar Area

Unlike other forms of power generation (wind, waves, generators), PV panels take solar area away from other needs such as greenhouses. This is especially bad because they use the sunlight which falls on them so inefficiently.

Despite these disadvantages, they have a proven track record for remote power generation, and have a place in a well-rounded power generation system for seasteads. Typical insolation is 1 KW/m², but only 13% of this is captured. There are about 1,750-2200 hours/year of full usable sunlight (at least on land - might be a little higher on the ocean with the low horizon). This gives about 0.25 MWhrs/m²/yr. The average PV system costs about $10,000/kW [RingEco] of installed capacity. Using that 1750-2250 number again, we see that a kW generates around 2 MWHrs/year. So PV systems are about $5,000/person, and around $2,000 for a kWhr per day.

Direct Solar

One thing you might have noticed when reading about PV is just how inefficient it is at converting sunlight to electricity (about 13%). This is especially annoying because it is so expensive. For this reason, its usually better (when possible) to use sunlight directly. This makes life more complicated than just doing everything with electricity, but in an environment of limited energy resources, its still a win.

There's no clever way to run your computer directly from sunlight without using electricity. But a large portion of home power usage is for heating: both spaces and water. As anyone who has walked across pavement in bare feet on a sunny day knows, all you have to do to turn something into a sunlight-to-heat conversion device is paint it black. Even simple solar water heaters are about 30% efficient, and cheap compared to PV panels. More complex designs are more efficient.

There are many other applications of direct solar, such as water distillation, space heating, laundry and dish drying. Its unclear just how many we'll use, since it depends on the energy available from other sources, how much money is available to spend on power systems, and so forth. Space heating, water heating and distillation are the main applications that we think will be commonly used.

Wind Power

Like solar power, wind power is a fairly mature technology that has been around for quite a while. The references we used for wind power were Harnessing the Wind for Home Energy by Dermot McGuigan [McGuigan1978]; and Wind Power Basics [Gipe1999]. As with photovoltaics, there are numerous appropriate alternative books on the subject. Again, most of these books start out with a statement of the form 'we are running out of energy' that should be discounted.

Wind power has two major advantage over photovoltaic generation. The first is 24-hour a day power extraction is possible. While there are times when the wind dies down, seasteads will likely spend much of their time in places where the "trade winds" blow continuously. Wind energy rises as the cube of wind velocity, so a steadier wind at the same average velocity provides significantly less energy than a variable wind. However, there are big benefits to consistent winds, such as reduced dependence on costly storage systems. The second is that raised wind turbines have essentially zero footprint and will not reduce top-deck area, which is needed for food production. Winds are stronger the higher you go above flat terrain, which is great for our seasteads that tower above the ocean. Experiments have shown that to raise a turbine from 18m to 30m increases power by 25%.

International Wind Energy Map

(Map prepared by NREL, click for larger image)

Wind turbines can be a bit loud, and elevating them out of the way involves guy wires - more difficult on a small seastead platform than land. Another disadvantage is that some of the wind's energy pushes the seastead. Some experiments will need to be performed with wind power to figure out how severe the wind pushing problem is. Fortunately wind and current directions are not usually parallel (trade winds are perpendicular), otherwise we would lose further velocity because drifting with the current would reduce the apparent wind velocity. Given the large size of a seastead and the small area likely to be used for wind turbines, this pushing should not be much of a problem.

{There is tons of data on wind speed available from the NOAA's NDBC data buoys. We can get data from there and estimate how much power is available.} The energy produced by wind turbines depend a great deal on wind velocity (because of the cube law), thus it is difficult to estimate how much power will be produced without knowing the details of local conditions. It looks like to generate 1 MWhr/year, we need about a 600 watt turbine. Small wind systems seem to cost around $3K / Kw, so that's $1800 / person. A large system for a decent sized seastead might be only half that price. Wind power has higher maintenance costs than solar, ie (for large power operators) 1.5 cents/KWhr, which is $14/p/ yr for us.

The seastead is free to use any form of turbine; they all work with varying degrees of efficiency. One design with interesting DIY possibilities is the Savonius rotor, sometimes referred to as an oil drum rotor. A cross section of a Savonius rotor, which consists of two half-cylinders, is shown below:

The Savonius rotor is a very inefficient design, which means more weight to be lofted. However, it also looks like its very easy to fabricate, since many Savonius rotors are manufactured out of old oil drums. Cut off the top and bottom, chop it in half, weld two of the edges together, and you have a rotor. Ultimately, what matters is not wind mill efficiency, but cost times efficiency. If cost is sufficiently low, additional power is obtained by simply erecting additional wind mills. Conveniently, Savonius rotors can be stacked on top of one another.

Fuel-Powered Generator

Renewable energy generators are great for self-sufficiency and long time-horizons. Once a seastead has installed enough PV panels and wind turbines, it does not need to import energy. However, renewable methods have some disadvantages. They are currently pretty expensive, they can't produce big spikes of power for occasional high demand, and they don't generate power constantly. Generators, which burn fuel to create electricity, address all of these issues. They can be run at any time, are cheap to operate, produce a lot of energy, and fuel (unlike a battery) is a dense form of energy storage with an excellent shelf life.

In general, fuel-powered generators seem best suited as a backup power source. For major power needs (welding) and during windless nights with calm seas, there will be little choice but to fire them up or do without. However, there are some specialized groups that may depend solely on generators, and others that will avoid them entirely. Low-budget seasteaders may want electricity, yet not be able to afford to buy renewable equipment with its long payback period. Seasteaders with particularly low transportation costs or low local renewable energy levels may also wish to stick with generators. On the other hand, environmentally-minded groups who don't like generating greenhouse gasses might avoid them all together.

Burning diesel or biodiesel in a conventional generator is extremely price-effective. At $1.40/gal in the US, and about 12 kWhs produced per gallon of diesel, electricity generated from diesel costs $0.12/kWh in fuel. Biodiesel can be cheaper if a free source of used vegetable oil is found. Maintenance costs are very low ($0.004 - $0.010 / kWh) [Kozlowski2002]. Transportation costs are the major unknown variable. Bulk container shipping rates would have essentially no impact on the cost per kWhr, but until seasteads are major container ports, shipping to them will be a lot more expensive.

We should note that these figures don't count all the energy produced as heat from the generator. This heat can be recaptured from the exhaust gauses through air-water heat exchangers and used for water and space heating. When heat as well as electricity is useful, generators become even more cost-effective.

Generators are pretty cheap per installed kilowatt. For example, the Kubota GL6500S diesel engine produces 6Kw for $4300. That's 144 KWhrs/day, or about $30/KWhr/day of installed generating capacity. At 3 KWhrs/person/day, that would be $90/person of installed generating capacity. Not bad at all, and the price will be even lower for larger units.

While generators aren't the only place we'll use fuel, this is a good place to discuss what's available.

Gasoline

Gasoline should never be used on a seastead unless absolutely necessary. It is volatile, evaporating at temperatures above -45 ° Celsius (its "flash point"). This means that at normal earth temperatuers, it is constantly emitting flammable vapor, which is quite dangerous. Its also extremely toxic, as its decay products are benzene and a bunch of other nasty chemicals.

Diesel

Diesel is a much mellower fuel, only vaporizing at temperatures above +50 ° Celsius, which are unlikely to be found in a seastead. The higher a fuel's flash point, the safer it is to store and handle. Diesel engines have a much simpler design, thus they require much less service and are more durable. Their exhaust also has many fewer toxic emissions than gasoline. They are much more efficient at turning fuel into electricity. Diesel engines are more expensive, but they are well worth it.

Biodiesel is harder to find internationally than diesel. It burns more cleanly, and is easy to make from vegetable oil. It has an even higher flash point than normal diesel. It is possible that a seastead could buy large amounts of used vegetable oil cheaply and make biodiesel for less than conventional diesel. Growing it is not likely to be practical due to surface area limitations.

Hydrogen

Hydrogen is a simple form of stored fuel, and quite safe (despite popular misconceptions). The bright flames from the Hindenburg zeppelin came from the lacquered covering, as most of the hydrogen escaped and did not burn [APS2000]. Hydrogen is lighter than air and disperses easily, so it does